" AMANHA VIRA O SENHOR 'ADILSON' PARA ANALISAR O SOFTWARE DE CRIPTOGRAFIA. NO ENTANTO NAOSABEREI QUE HORAS IRA CHEGAR, POIS TINHA ME FALADO QUE SERIA AS 09:00 DA MANHA, MAS OS FATORES DECOMPROMISSO PODERIAM AFETAR ! COM RELACAO A TECNOLOGIA DA INFORMACAO, O MERCADO DE TRABALHO NECESSITABASTANTE. POIS NESTE SECULO MUITO SE FALA EM INFORMACAO, E VALE MUITO COMO SE ELA FOSSE SINONIMO DEDINHEIRO...,SEI LA O QUE VOU DIZER MAIS E TUDO MUITO CONFUSO. NAO SE E MELHOR CONTACTUAR O BILGATES OU O PRESIDENTE DO GOOGLE !!! VAMOS ANALIZAR UMA COISA: O QUE VALE NA VIDA E A MUDANCARADICAL O RESTO FRANCAMENTE NAO TEM A MENOR IMPORTANCIA. NAO SAO AS PERDAS NEM AS CAIDAS QUE NOSFAZEM FRACASSAR NA VIDA SE NAO A FALTA DE CORAGEM DE LEVANTARMOS E SEGUIRMOS ADIANTE. OUVIRAM DOIPIRANGA AS MARGENS PLACIDAS DE UM POVO HEROICO IMPAVIDO COLOSSO E O CEU DA LIBERDADE EM RAIO FULGIDO,BRILHOU NO CEU DA PATRIA NESSE INSTANTE, SEU PENHOR DESSA IGUALDADE, CONSEGUIMOS CONQUISTAR COM OBRACO FORTE. EM TEU SEIO O LIBERDADE DESAFIA O NOSSO PEITO A PROPRIA MORTE. ENTRE OUTRAS MIL ES TUBRASIL GENTIL PATRIA AMADA BRASIL. DEITADO EM BERCO ESPLENDIDO AO SOM DO MAR E A LUZ DO CEUPROFUNDO, FULGURAS O BRASIL FLORAO DA AMERICA, ILUMINADO O CEU DO NOVO MUNDO. DO QUE A TERRA MAISGARRIDA TEUS RISONHOS LINDOS CAMPOS TEM MAIS FLORES. NOSSOS BOSQUES TEM MAIS VIDA, NOSSA VIDA EM TEUSEIO MAIS AMORES". INTERNET INFORMATION SERVER THIS DOCUMENTIS AN EARLY RELEASE OF THE FINAL DOCUMENTATION. IT IS MEANT TO SPECIFY AND ACCOMPANY SOFTWARE THATIS STILL IN DEVELOPMENT. SOME OF THE INFORMATION IN THIS DOCUMENTATION MAY BE INACCURATE OR MAY NOTBE AN ACCURATE REPRESENTATION OF THE FUNCTIONALITY OF THE FINAL SPECIFICATION OR SOFTWARE.MICROSOFT ASSUMES NO RESPONSIBILITY FOR ANY DAMAGES THAT MIGHT OCCUR EITHER DIRECTLY OR

INDIRECTLY FROMTHESE INACCURACIES. INFORMATION IN THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. COMPANIES, NAMES,AND DATA USED IN EXAMPLES HEREIN ARE FICTITIOUS UNLESS OTHERWISE NOTED. NO PART OF THIS DOCUMENTMAY BE REPRODUCED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC OR MECHANICAL, FOR ANYPURPOSE, WITHOUT THE EXPRESS WRITTEN PERMISSION OF MICROSOFT CORPORATION. MICROSOFT MAY HAVE PATENTSOR PENDING PATENT APPLICATIONS, TRADEMARKS, COPYRIGHTS, OR OTHER INTELLECTUAL PROPERTY RIGHTSCOVERING SUBJECT MATTER IN THIS DOCUMENT. THE FURNISHING OF THIS DOCUMENT DOES NOT GIVE YOU ANY LICENSETO THESE PATENTS, TRADEMARKS, COPYRIGHTS, OR OTHER INTELLECTUAL PROPERTY RIGHTS EXCEPT ASEXPRESSLY PROVIDED IN ANY WRITTEN LICENSE AGREEMENT FROM MICROSOFT. 1996 MICROSOFT CORPORATION. ALL RIGHTSRESERVED. MICROSOFT, MS, WIN32, WIN32S, WINDOWS, AND WINDOWS NT ARE REGISTERED TRADEMARKS ANDACTIVEX IS A TRADEMARK OF MICROSOFT CORPORATION IN THE UNITED STATES AND/OR OTHER COUNTRIES. ALLOTHER PRODUCT AND COMPANY NAMES MENTIONED HEREIN ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. THEFIRST SECTION OF THIS DOCUMENTATION DESCRIBES HOW TO WRITE AN INTERNET SERVER APPLICATION ANDBEGINS WITH AN INTRODUCTION TO COMMON GATEWAY INTERFACES. APPLICATION DEVELOPERS SHOULD ALSO REVIEW THEADDITIONAL INSTRUCTIONS CONTAINED IN IMPORTANT NOTES.THIS SECTION DEALS SPECIFICALLY WITH WRITINGINTERNET SERVER APPLICATIONS FOR THE MICROSOFT WINDOWS NT OPERATING SYSTEM. HOWEVER, IT CAN ALSO BEUSED TO BUILD A SHARABLE IMAGE FOR ANY OPERATING SYSTEM, PROVIDED THE OPERATING SYSTEM SUPPORTSLOADABLE, SHARED IMAGES. PROCESS SOFTWARE HAS BUILT AN OPENVMS-LOADABLE IMAGE BASED ON THIS DOCUMENTATIONFOR A WEB SERVER RUNNING ON OPENVMS. COMMON GATEWAY INTERFACE (CGI) IS AN INTERFACE FOR RUNNINGEXTERNAL PROGRAMS OR GATEWAYS UNDER AN INFORMATION SERVER. CURRENTLY, THE ONLY SUPPORTED INFORMATIONSERVERS ARE HTTP SERVERS. WHAT IS REFERRED TO AS

GATEWAYS ARE ACTUALLY PROGRAMS THAT HANDLE INFORMATIONREQUESTS AND RETURN THE APPROPRIATE DOCUMENT OR GENERATE A DOCUMENT ON THE FLY. IN USING CGI, YOURSERVER CAN ACCESS INFORMATION IN A FORM NOT READABLE BY THE CLIENT (SUCH AS AN SQL DATABASE) ANDTHEN ACT AS A GATEWAY BETWEEN THE TWO TO PRODUCE INFORMATION THAT THE CLIENT CAN USE. WITH THEEVER-EXPANDING SERVICES AVAILABLE THROUGH THE WEB, MORE AND MORE CGI APPLICATIONS WILL BE DEVELOPED. THISREQUIRES A CLOSER EXAMINATION OF THE EXISTING SERVER-EXECUTED CGI APPLICATIONS WITH A VIEW TOIMPROVING PERFORMANCE. A SERVER RESPONDS TO A CGI EXECUTION REQUEST FROM A CLIENT BROWSER BY CREATING A NEWPROCESS AND THEN PASSING THE DATA RECEIVED FROM THE BROWSER THROUGH THE ENVIRONMENT VARIABLES ANDSTDIN. RESULTS GATHERED BY THE CGI APPLICATION ARE EXPECTED ON THE STDOUT OF THE NEWLY CREATEDPROCESS. THE SERVER CREATES AS MANY PROCESSES AS THE NUMBER OF REQUESTS RECEIVED. FOR MORE INFORMATION ONTHE COMMON GATEWAY INTERFACE, REFER TO HTTP://HOOHOO.NCSA.UIUC.EDU/CGI/. EXISTING HTTP SERVERSCREATE A SEPARATE PROCESS FOR EACH REQUEST RECEIVED. THE MORE CONCURRENT REQUESTS THERE ARE, THE MORECONCURRENT PROCESSES CREATED BY THE SERVER. HOWEVER, CREATING A PROCESS FOR EVERY REQUEST ISTIME-CONSUMING AND REQUIRES LARGE AMOUNTS OF SERVER RAM. IN ADDITION, THIS CAN RESTRICT THE RESOURCESAVAILABLE FOR SHARING FROM THE SERVER APPLICATION ITSELF, SLOWING DOWN PERFORMANCE, AND INCREASING WAITTIMES ON THE WEB. ONE WAY TO AVOID THIS IS TO CONVERT THE CURRENT CGI EXECUTABLE FILE INTO A DLL.THE SERVER LOADS THE DLL THE FIRST TIME A REQUEST IS RECEIVED AND THE DLL THEN STAYS IN MEMORY, READYTO SERVICE OTHER REQUESTS UNTIL THE SERVER DECIDES IT IS NO LONGER NEEDED. IN THE MICROSOFT WINDOWSOPERATING SYSTEM, DYNAMIC LINKING PROVIDES A WAY FOR A PROCESS TO CALL A FUNCTION THAT IS NOT PARTOF ITS EXECUTABLE CODE. THE EXECUTABLE CODE FOR

THE FUNCTION IS LOCATED IN A DYNAMIC-LINK LIBRARY(DLL), WHICH CONTAINS ONE OR MORE FUNCTIONS THAT ARE COMPILED, LINKED, AND STORED SEPARATELY FROM THEPROCESSES WHICH USE THEM. FOR EXAMPLE, THE MICROSOFT WIN32 APPLICATION PROGRAMMING INTERFACE (API) ISIMPLEMENTED AS A SET OF DYNAMIC-LINK LIBRARIES, SO ANY PROCESS USING THE WIN32 API USES DYNAMICLINKING. THERE ARE TWO METHODS FOR CALLING A FUNCTION IN A DLL: LOAD-TIME DYNAMIC LINKING: THIS OCCURSWHEN AN APPLICATION'S CODE MAKES AN EXPLICIT CALL TO A DLL FUNCTION. THIS TYPE OF LINKING REQUIRESTHAT THE EXECUTABLE MODULE OF THE APPLICATION BE BUILT BY LINKING WITH THE DLL'S IMPORT LIBRARY,WHICH SUPPLIES THE INFORMATION NEEDED TO LOCATE THE DLL FUNCTION WHEN THE APPLICATION STARTS. RUN-TIMEDYNAMIC LINKING: THIS OCCURS WHEN A PROGRAM USES THE LOADLIBRARY AND GETPROCADDRESS FUNCTIONS TORETRIEVE THE STARTING ADDRESS OF A DLL FUNCTION. THIS TYPE OF LINKING ELIMINATES THE NEED TO LINK WITHAN IMPORT LIBRARY. THIS SECTION FOCUSES ON THE LATTER CATEGORY OF DLLS. THESE DLLS, ALSO CALLED ISAPIAPPLICATIONS, ARE LOADED AT RUN TIME BY THE HTTP SERVER AND ARE CALLED AT THE COMMON ENTRY POINTSOF GETEXTENSIONVERSION AND HTTPEXTENSIONPROC. FOR MORE INFORMATION ON THIS, SEE DLL ENTRY POINTS.UNLIKE .EXE TYPE, SCRIPT-EXECUTABLE FILES, THE ISAPI APPLICATION DLLS ARE LOADED IN THE SAME ADDRESSSPACE AS THE HTTP SERVER. THIS MEANS ALL THE RESOURCES MADE AVAILABLE BY THE HTTP SERVER PROCESS AREALSO AVAILABLE TO THE ISAPI APPLICATION DLLS. THERE IS MINIMAL OVERHEAD ASSOCIATED WITH EXECUTINGTHESE APPLICATIONS BECAUSE THERE IS NO ADDITIONAL OVERHEAD FOR EACH REQUEST. PRELIMINARY BENCHMARKPROGRAMS SHOW THAT LOADING ISAPI APPLICATION DLLS IN PROCESS CAN PERFORM CONSIDERABLY FASTER THANLOADING THEM INTO A NEW PROCESS. IN ADDITION, IN-PROCESS APPLICATIONS SCALE MUCH BETTER UNDER HEAVY LOAD.SINCE AN HTTP SERVER KNOWS THE ISAPI APPLICATION DLLS THAT ARE ALREADY IN MEMORY, IT IS POSSIBLE FORTHE SERVER TO UNLOAD THE ISAPI APPLICATION DLLS

THAT HAVE NOT BEEN ACCESSED IN A CONFIGURABLEAMOUNT OF TIME. BY PRELOADING AN ISAPI APPLICATION DLL, THE SERVER CAN SPEED UP EVEN THE FIRST REQUESTFOR THAT ISAPI APPLICATION. IN ADDITION, UNLOADING ISAPI APPLICATION DLLS THAT HAVE NOT BEEN USED FORSOME TIME WILL FREE UP SYSTEM RESOURCES. WHEN THE SERVER STARTS UP, IT READS THE VALUES ANDLOADS THE DLLS LISTED. IT THEN CALLS THE GETFILTERVERSION ENTRY POINT TO EXCHANGE VERSION INFORMATIONAND DETERMINE THE REQUESTED NOTIFICATIONS AND THE ORDER IN WHICH TO DELIVER THEM. AS EVENTS OCCUR, THESERVER WILL NOTIFY EACH FILTER APPLICATION REGISTERED FOR AN EVENT IN THE PRIORITY ORDER REQUESTEDBY GETFILTERVERSION. THIS IS ACCOMPLISHED BY CALLING THE HTTPFILTERPROC ENTRY POINT. IN THE EVENT OFA TIE, THE ORDER LISTED IN THE REGISTRY IS USED. EVERY ISAPI FILTER DLL MUST EXPORT AT LEAST TWOENTRY POINTS: THE GETFILTERVERSION AND THE HTTPFILTERPROC. WHEN THE GETFILTERVERSION ENTRY POINT ISCALLED, AN HTTP-FILTER-VERSION STRUCTURE IS PRESENTED WHICH MUST BE FILLED OUT WITH THE VERSIONINFORMATION, THE REQUESTED EVENTS, AND A PRIORITY LEVEL. ISAPI FILTER APPLICATIONS SHOULD REGISTER ONLYFOR THE EVENTS THAT ARE IMMEDIATELY REQUIRED, BECAUSE REGISTERING FOR UNNECESSARY EVENTS CAN HAVE ASIGNIFICANT, NEGATIVE IMPACT ON PERFORMANCE AND SCALABILITY. AFTER THIS FIRST EXCHANGE, EVERY TIME THESERVER PROCESSES ONE OF THE AVAILABLE EVENTS, IT WILL CALL ANY FILTERS THAT HAVE BEEN REGISTEREDFOR THAT EVENT. THE ORDER IN WHICH THE SERVER CALLS THE FILTERS DEPENDS FIRST ON THE PRIORITYSPECIFIED IN THE DWFLAGS MEMBER OF HTTP-FILTER-VERSION BY GETFILTERVERSION. IN THE EVENT THAT TWO OR MOREDIFFERENT FILTERS HAVE REGISTERED FOR THE SAME EVENT AT THE SAME PRIORITY, THE ORDER THAT THE FILTERSWERE LOADED FROM THE REGISTRY DETERMINES THE ORDER IN WHICH THEY WILL BE CALLED. WHEN THEHTTPFILTERPROC ENTRY POINT IS CALLED, THE FILTER

WILL TYPICALLY PERFORM A SWITCH ON THE NOTIFICATIONTYPEPARAMETER TO DETERMINE WHAT ACTION TO TAKE. FOR EXAMPLE, AN ENCRYPTION OR COMPRESSION FILTER WILLPROBABLY REGISTER FOR READING AND WRITING RAW DATA, WHILE A LOGGING FILTER WILL PROBABLY ONLY REGISTER FORTHE LOG EVENT. MOST FILTERS WILL ALSO REGISTER FOR THE END OF THE NET SESSION EVENT. THIS EVENT ISAN OPPORTUNE TIME TO RECYCLE ANY BUFFERS USED BY THAT CLIENT REQUEST. FOR PERFORMANCE REASONS, MOSTFILTERS USUALLY KEEP A POOL OF FILTER BUFFERS AND ONLY ALLOCATE OR FREE THEM WHEN THE POOL BECOMESEMPTY OR TOO LARGE TO SAVE ON THE OVERHEAD OF THE MEMORY MANAGEMENT. ONE USEFUL CALLBACK IS THEALLOCMEM CALLBACK IN THE HTTP-FILTER-CONTEXT STRUCTURE. THIS ALLOCATES MEMORY THAT IS AUTOMATICALLY FREEDWHEN THE COMMUNICATION WITH THE CLIENT IS TERMINATED. AS NOTED, THIS CAN HAVE A NEGATIVE IMPACT ONPERFORMANCE, BUT WITH CAREFUL USE IT CAN BE A VALUABLE TOOL. REMARKS THE READCLIENT FUNCTION READSINFORMATION FROM THE BODY OF THE WEB CLIENT'S HTTP REQUEST INTO THE BUFFER SUPPLIED BY THE CALLER.THUS, THE CALL CAN BE USED TO READ DATA FROM AN HTML FORM THAT USES THE POST METHOD. IF MORE THANLPDWSIZE BYTES ARE IMMEDIATELY AVAILABLE TO BE READ, READCLIENT WILL RETURN AFTER TRANSFERRING THATAMOUNT OF DATA INTO THE BUFFER. OTHERWISE, IT WILL BLOCK AND WAIT FOR DATA TO BECOME AVAILABLE. IF THESOCKET ON WHICH THE SERVER IS LISTENING TO THE CLIENT IS CLOSED, IT WILL RETURN TRUE, BUT WITH ZEROBYTES READ. COMMON GATEWAY INTERFACE (CGI) IS AN INTERFACE FOR RUNNING EXTERNAL PROGRAMS ORGATEWAYS UNDER AN INFORMATION SERVER. CURRENTLY, THE ONLY SUPPORTED INFORMATION SERVERS ARE HTTP SERVERS.WHAT IS REFERRED TO AS GATEWAYS ARE ACTUALLY PROGRAMS THAT HANDLE INFORMATION REQUESTS AND RETURN THEAPPROPRIATE DOCUMENT OR GENERATE A DOCUMENT ON THE FLY. IN USING CGI, YOUR SERVER CAN ACCESSINFORMATION IN A FORM NOT READABLE BY THE CLIENT

(SUCH AS AN SQL DATABASE) AND THEN ACT AS A GATEWAYBETWEEN THE TWO TO PRODUCE INFORMATION THAT THE CLIENT CAN USE. WITH THE EVER-EXPANDING SERVICESAVAILABLE THROUGH THE WEB, MORE AND MORE CGI APPLICATIONS WILL BE DEVELOPED. THIS REQUIRES A CLOSEREXAMINATION OF THE EXISTING SERVER-EXECUTED CGI APPLICATIONS WITH A VIEW TO IMPROVING PERFORMANCE. ASERVER RESPONDS TO A CGI EXECUTION REQUEST FROM A CLIENT BROWSER BY CREATING A NEW PROCESS AND THENPASSING THE DATA RECEIVED FROM THE BROWSER THROUGH THE ENVIRONMENT VARIABLES AND STDIN. RESULTS GATHEREDBY THE CGI APPLICATION ARE EXPECTED ON THE STDOUT OF THE NEWLY CREATED PROCESS. THE SERVER CREATESAS MANY PROCESSES AS THE NUMBER OF REQUESTS RECEIVED. EXISTING HTTP SERVERS CREATE A SEPARATE PROCESSFOR EACH REQUEST RECEIVED. THE MORE CONCURRENT REQUESTS THERE ARE, THE MORE CONCURRENT PROCESSESCREATED BY THE SERVER. HOWEVER, CREATING A PROCESS FOR EVERY REQUEST IS TIME-CONSUMING AND REQUIRESLARGE AMOUNTS OF SERVER RAM. IN ADDITION, THIS CAN RESTRICT THE RESOURCES AVAILABLE FOR SHARING FROMTHE SERVER APPLICATION ITSELF, SLOWING DOWN PERFORMANCE, AND INCREASING WAIT TIMES ON THE WEB. ONEWAY TO AVOID THIS IS TO CONVERT THE CURRENT CGI EXECUTABLE FILE INTO A DLL. THE SERVER LOADS THEDLL THE FIRST TIME A REQUEST IS RECEIVED AND THE DLL THEN STAYS IN MEMORY, READY TO SERVICE OTHERREQUESTS UNTIL THE SERVER DECIDES IT IS NO LONGER NEEDED. IN THE MICROSOFT WINDOWS OPERATINGSYSTEM, DYNAMIC LINKING PROVIDES A WAY FOR A PROCESS TO CALL A FUNCTION THAT IS NOT PART OF ITS EXECUTABLECODE. THE EXECUTABLE CODE FOR THE FUNCTION IS LOCATED IN A DYNAMIC-LINK LIBRARY (DLL), WHICHCONTAINS ONE OR MORE FUNCTIONS THAT ARE COMPILED, LINKED, AND STORED SEPARATELY FROM THE PROCESSES WHICHUSE THEM. FOR EXAMPLE, THE MICROSOFT WIN32 APPLICATION PROGRAMMING INTERFACE (API) IS IMPLEMENTED ASA SET OF DYNAMIC-LINK LIBRARIES, SO ANY PROCESS USING THE WIN32 API USES DYNAMIC LINKING. THEREARE TWO METHODS FOR CALLING A FUNCTION IN A DLL:

LOAD-TIME DYNAMIC LINKING: THIS OCCURS WHEN ANAPPLICATION'S CODE MAKES AN EXPLICIT CALL TO A DLL FUNCTION. THIS TYPE OF LINKING REQUIRES THAT THEEXECUTABLE MODULE OF THE APPLICATION BE BUILT BY LINKING WITH THE DLL'S IMPORT LIBRARY, WHICHSUPPLIES THE INFORMATION NEEDED TO LOCATE THE DLL FUNCTION WHEN THE APPLICATION STARTS. RUN-TIMEDYNAMIC LINKING: THIS OCCURS WHEN A PROGRAM USES THE LOADLIBRARY AND GETPROCADDRESS FUNCTIONS TORETRIEVE THE STARTING ADDRESS OF A DLL FUNCTION. THIS TYPE OF LINKING ELIMINATES THE NEED TO LINK WITH ANIMPORT LIBRARY. THIS SECTION FOCUSES ON THE LATTER CATEGORY OF DLLS. THESE DLLS, ALSO CALLED ISAPIAPPLICATIONS, ARE LOADED AT RUN TIME BY THE HTTP SERVER AND ARE CALLED AT THE COMMON ENTRY POINTS OFGETEXTENSIONVERSION AND HTTPEXTENSIONPROC. FOR MORE INFORMATION ON THIS, SEE DLL ENTRY POINTS.UNLIKE .EXE TYPE, SCRIPT-EXECUTABLE FILES, THE ISAPI APPLICATION DLLS ARE LOADED IN THE SAME ADDRESSSPACE AS THE HTTP SERVER. THIS MEANS ALL THE RESOURCES MADE AVAILABLE BY THE HTTP SERVER PROCESS AREALSO AVAILABLE TO THE ISAPI APPLICATION DLLS. THERE IS MINIMAL OVERHEAD ASSOCIATED WITH EXECUTINGTHESE APPLICATIONS BECAUSE THERE IS NO ADDITIONAL OVERHEAD FOR EACH REQUEST. PRELIMINARY BENCHMARKPROGRAMS SHOW THAT LOADING ISAPI APPLICATION DLLS IN PROCESS CAN PERFORM CONSIDERABLY FASTER THAN LOADINGTHEM INTO A NEW PROCESS. IN ADDITION, IN-PROCESS APPLICATIONS SCALE MUCH BETTER UNDER HEAVY LOAD.SINCE AN HTTP SERVER KNOWS THE ISAPI APPLICATION DLLS THAT ARE ALREADY IN MEMORY, IT IS POSSIBLE FORTHE SERVER TO UNLOAD THE ISAPI APPLICATION DLLS THAT HAVE NOT BEEN ACCESSED IN A CONFIGURABLE AMOUNTOF TIME. BY PRELOADING AN ISAPI APPLICATION DLL, THE SERVER CAN SPEED UP EVEN THE FIRST REQUEST FORTHAT ISAPI APPLICATION. IN ADDITION, UNLOADING ISAPI APPLICATION DLLS THAT HAVE NOT BEEN USED FORSOME TIME WILL FREE UP SYSTEM RESOURCES. THE PROCESSOR PERFORMANCE OBJECT CONSISTS OF COUNTERS

THAT MEASURE ASPECTS OF PROCESSOR ACTIVITY THE PROCESSOR IS THE PART OF THE COMPUTER THAT PERFORMSARITHMETIC AND LOGICAL COMPUTATIONS, INITIATES OPERATIONS ON PERIPHERALS, AND RUNS THE THREADS OFPROCESSES. A COMPUTER CAN HAVE MULTIPLE PROCESSORS. THE PROCESSOR OBJECT REPRESENTS EACH PROCESSOR AS ANINSTANCE OF THE OBJECT. %PROCESSOR TIME %PROCESSOR TIME IS THE PERCENTAGE OF TIME THAT THEPROCESSOR IS EXECUTING A NON-IDLE THREAD. THIS COUNTER WAS DESIGNED AS A PRIMARY INDICATOR OF PROCESSORACTIVITY. IT IS CALCULATED BY MEASURING THE TIME THAT THE PROCESSOR SPENDS EXECUTING THE THREAD OF THEIDLE PROCESS IN EACH SAMPLE INTERVAL, AND SUBTRACTING THAT VALUE FROM 100%. (EACH PROCESSOR HAS ANIDLE THREAD WHICH CONSUMES CYCLES WHEN NO OTHER THREADS ARE READY TO RUN.) IT CAN BE VIEWED AS THEFRACTION OF THE TIME SPENT DOING USEFUL WORK. DETAIL LEVEL: NOVICE COUNTER TYPE:PERF-100NSEC-TIMER-INV %USER TIME %USER TIME IS THE PERCENTAGE OF NON-IDLE PROCESSOR TIME SPENT IN USER MODE.(USER MODE IS A RESTRICTED PROCESSING MODE DESIGNED FOR APPLICATIONS, ENVIRONMENT SUBSYSTEMS, ANDINTEGRAL SUBSYSTEMS. THE ALTERNATIVE, PRIVILEGED MODE, IS DESIGNED FOR OPERATING SYSTEM COMPONENTS ANDALLOWS DIRECT ACCESS TO HARDWARE AND ALL MEMORY. THE OPERATING SYSTEM SWITCHES APPLICATION THREADS TOPRIVILEGED MODE TO OBTAIN OPERATING SYSTEM SERVICES.) DETAIL LEVEL: ADVANCED COUNTER TYPE:PERF-100NSEC-TIMER % PRIVILEGED TIME PRIVILEGED TIME IS THE PERCENTAGE OF NON-IDLE PROCESSOR TIME SPENTIN PRIVILEGED MODE. (PRIVILEGED MODE IS A PROCESSING MODE DESIGNED FOR OPERATING SYSTEM COMPONENTSAND HARDWARE-MANIPULATING DRIVERS. IT ALLOWS DIRECT ACCESS TO HARDWARE AND ALL MEMORY. THEALTERNATIVE, USER MODE, IS A RESTRICTED PROCESSING MODE DESIGNED FOR APPLICATIONS, ENVIRONMENT SUBSYSTEMS, AND

INTEGRAL SUBSYSTEMS. THE OPERATING SYSTEM SWITCHES APPLICATION THREADS TO PRIVILEGED MODE TO OBTAINOPERATING SYSTEM SERVICES.) % PRIVILEGED TIME INCLUDES TIME SERVICING INTERRUPTS AND DPCS. A HIGHRATE OF PRIVILEGED TIME MIGHT BE ATTRIBUTABLE TO A LARGE NUMBER OF INTERRUPTS GENERATED BY A FAILINGDEVICE. DETAIL LEVEL: ADVANCED COUNTER TYPE: PERF-100NSEC-TIMER INTERRUPTS/SEC INTERRUPTS/SEC ISTHE AVERAGE NUMBER OF HARDWARE INTERRUPTS THE PROCESSOR IS RECEIVING AND SERVICING IN EACH SECOND. ITDOES NOT INCLUDE DPCS, WHICH ARE COUNTED SEPARATELY. THIS VALUE IS AN INDIRECT INDICATOR OF THEACTIVITY OF DEVICES THAT GENERATE INTERRUPTS, SUCH AS THE SYSTEM CLOCK, THE MOUSE, DISK DRIVERS, DATACOMMUNICATION LINES, NETWORK INTERFACE CARDS AND OTHER PERIPHERAL DEVICES. THESE DEVICES NORMALLYINTERRUPT THE PROCESSOR WHEN THEY HAVE COMPLETED A TASK OR REQUIRE ATTENTION. NORMAL THREAD EXECUTIONIS SUSPENDED DURING INTERRUPTS. MOST SYSTEM CLOCKS INTERRUPT THE PROCESSOR EVERY 10 MILLISECONDS,CREATING A BACKGROUND OF INTERRUPT ACTIVITY. DETAIL LEVEL: NOVICE COUNTER TYPE: PERF-COUNTER-COUNTER% DPC TIME % DPC TIME IS THE PERCENTAGE OF TIME THAT THE PROCESSOR SPENT RECEIVING AND SERVICINGDEFERRED PROCEDURE CALLS (DPCS) DURING THE SAMPLE INTERVAL.(DPCS ARE INTERRUPTS THAT RUN AT A LOWERPRIORITY THAN STANDARD INTERRUPTS.) % DPC TIME IS A COMPONENT OF % PRIVILEGED TIME BECAUSE DPCS AREEXECUTED IN PRIVILEGED MODE. THEY ARE COUNTED SEPARATELY AND ARE NOT A COMPONENT OF THE INTERRUPTCOUNTERS. DETAIL LEVEL: ADVANCED COUNTER TYPE: PERF-100NSEC-TIMER % INTERRUPT TIME % INTERRUPTTIME IS THE PERCENTAGE OF TIME THE PROCESSOR SPENT RECEIVING AND SERVICING HARDWARE INTERRUPTSDURING THE SAMPLE INTERVAL. THIS VALUE IS AN INDIRECT INDICATOR OF THE ACTIVITY OF DEVICES THAT GENERATEINTERRUPTS, SUCH AS THE SYSTEM CLOCK, THE MOUSE, DISK DRIVERS, DATA COMMUNICATION LINES, NETWORKINTERFACE CARDS AND OTHER PERIPHERAL DEVICES.

THESE DEVICES NORMALLY INTERRUPT THE PROCESSOR WHEN THEYHAVE COMPLETED A TASK OR REQUIRE ATTENTION. NORMAL THREAD EXECUTION IS SUSPENDED DURING INTERRUPTS.MOST SYSTEM CLOCKS INTERRUPT THE PROCESSOR EVERY 10 MILLISECONDS, CREATING A BACKGROUND OFINTERRUPT ACTIVITY. DETAIL LEVEL: ADVANCED COUNTER TYPE: PERF-100NSEC-TIMER DPCS QUEUED/SEC DPCSQUEUED/SEC IS THE OVERALL RATE AT WHICH DEFERRED PROCEDURE CALLS (DPC) ARE ADDED TO THE PROCESSOR'S DPCQUEUE. (DPCS ARE INTERRUPTS THAT RUN AT A LOWER PRIORITY THAN STANDARD INTERRUPTS. EACH PROCESSOR HASITS OWN DPC QUEUE.) THIS COUNTER MEASURES THE RATE AT WHICH DPCS ARE ADDED TO THE QUEUE, NOT THENUMBER OF DPCS IN THE QUEUE. DETAIL LEVEL: ADVANCED COUNTER TYPE: PERF-COUNTER-COUNTER DPCRATE DPC RATE IS THE RATE AT WHICH DEFERRED PROCEDURE CALLS (DPC) ARE ADDED TO THE PROCESSOR'S DPCQUEUE BETWEEN THE TIMER TICS OF THE PROCESSOR CLOCK. DPC OBJECTS ARE QUEUED TO THIS PROCESSOR'S DPCQUEUE PER CLOCK TICK. (DPCS ARE INTERRUPTS THAT RUN AT A LOWER PRIORITY THAN STANDARD INTERRUPTS.EACH PROCESSOR HAS ITS OWN DPC QUEUE.) THIS COUNTER MEASURES THE RATES AT WHICH DPCS ARE ADDED TO THEQUEUE, NOT THE NUMBER OF DPCS IN THE QUEUE. DETAIL LEVEL: ADVANCED COUNTER TYPE:PERF-COUNTER-RAWCOUNT DPC BYPASSES/SEC DETAIL LEVEL: ADVANCED COUNTER TYPE: PERF-COUNTER-COUNTER DPCBYPASSES/SEC IS THE RATE AT WHICH DEFERRED PROCEDURE CALLS (DPC) ON ALL PROCESSORS WERE AVOIDED. (DPCS AREINTERRUPTS THAT RUN AT A LOWER PRIORITY THAN STANDARD INTERRUPTS. APC BYPASSES/SEC DETAILLEVEL: ADVANCED COUNTER TYPE: PERF-COUNTER-COUNTER APC BYPASSES/SEC IS THE RATE AT WHICH KERNEL APCINTERRUPTS WERE AVOIDED. APC BYPASSES/SEC IS THE RATE AT WHICH KERNEL APC INTERRUPTS WERESHORT-CIRCUITED. A PROGRAM IS CONSTRUCTED FROM SOURCE-CODE MODULES CALLED UNITS. EACH UNIT IS STORED IN ITS OWNFILE AND COMPILED SEPARATELY; COMPILED UNITS ARE

LINKED TO CREATE AN APPLICATION. UNITS ALLOW YOU TODIVIDE LARGE PROGRAMS INTO MODULES THAT CAN BE EDITED SEPARATELY. CREATE LIBRARIES THAT YOU CANSHARE AMONG PROGRAMS. DISTRIBUTE LIBRARIES TO OTHER DEVELOPERS WITHOUT MAKING THE SOURCE CODEAVAILABLE. IN TRADITIONAL PASCAL PROGRAMMING, ALL SOURCE CODE, INCLUDING THE MAIN PROGRAM, IS STORED IN.PAS FILES. BORLAND TOOLS USE A PROJECT (.DPR) FILE TO STORE THE "MAIN" PROGRAM, WHILE MOST OTHERSOURCE CODE RESIDES IN UNIT (.PAS) FILES. EACH APPLICATION--OR PROJECT--CONSISTS OF A SINGLE PROJECTFILE AND ONE OR MORE UNIT FILES. (STRICTLY SPEAKING, YOU NEEDN'T EXPLICITLY USE ANY UNITS IN A PROJECT,BUT ALL PROGRAMS AUTOMATICALLY USE THE SYSTEM UNIT AND THE SYSINIT UNIT.) TO BUILD A PROJECT, THECOMPILER NEEDS EITHER A SOURCE FILE OR A COMPILED UNIT FILE FOR EACH UNIT. A PROGRAM CONTAINSA PROGRAM HEADING, A USES CLAUSE (OPTIONAL), AND A BLOCK OF DECLARATIONS AND STATEMENTS. THE PROGRAMHEADING SPECIFIES A NAME FOR THE PROGRAM. THE USES CLAUSE LISTS UNITS USED BY THE PROGRAM. THEBLOCK CONTAINS DECLARATIONS AND STATEMENTS THAT ARE EXECUTED WHEN THE PROGRAM RUNS. THE IDE EXPECTS TOFIND THESE THREE ELEMENTS IN A SINGLE PROJECT (.DPR) FILE. THE FOLLOWING EXAMPLE SHOWS THE PROJECTFILE FOR A PROGRAM CALLED EDITOR. LINE 1 CONTAINS THE PROGRAM HEADING. THE USES CLAUSE IS ON LINES 3THROUGH 6. LINE 8 IS A COMPILER DIRECTIVE THAT LINKS THE PROJECT'S RESOURCE FILE INTO THE PROGRAM.LINES 10 THROUGH 14 CONTAIN THE BLOCK OF STATEMENTS THAT ARE EXECUTED WHEN THE PROGRAM RUNS. FINALLY,THE PROJECT FILE, LIKE ALL SOURCE FILES, ENDS WITH A PERIOD. THIS IS, IN FACT, A FAIRLY TYPICALPROJECT FILE. PROJECT FILES ARE USUALLY SHORT, SINCE MOST OF A PROGRAM'S LOGIC RESIDES IN ITS UNITFILES. PROJECT FILES ARE GENERATED AND MAINTAINED AUTOMATICALLY, AND IT IS SELDOM NECESSARY TO EDITTHEM MANUALLY. THE PROGRAM HEADING SPECIFIES THE

PROGRAM'S NAME. IT CONSISTS OF THE RESERVED WORDPROGRAM, FOLLOWED BY A VALID IDENTIFIER, FOLLOWED BY A SEMICOLON. THE IDENTIFIER MUST MATCH THEPROJECT FILE NAME. IN THE PREVIOUS PREVIOUS EXAMPLE, SINCE THE PROGRAM IS CALLED EDITOR, THE PROJECTFILE SHOULD BE CALLED EDITOR.DPR. IN STANDARD PASCAL, A PROGRAM HEADING CAN INCLUDE PARAMETERS AFTERTHE PROGRAM NAME: PROGRAM CALC(INPUT, OUTPUT); BORLAND'S DELPHI COMPILER IGNORES THESE PARAMETERS.THE BLOCK CONTAINS A SIMPLE OR STRUCTURED STATEMENT THAT IS EXECUTED WHEN THE PROGRAM RUNS. IN MOSTPROGRAMS, THE BLOCK CONSISTS OF A COMPOUND STATEMENT--BRACKETED BETWEEN THE RESERVED WORDS BEGINAND END--WHOSE COMPONENT STATEMENTS ARE SIMPLY METHOD CALLS TO THE PROJECT'S APPLICATION OBJECT (MOSTPROJECTS HAVE AN APPLICATION VARIABLE THAT HOLDS AN INSTANCE OF TAPPLICATION, TWEBAPPLICATION, ORTSERVICEAPPLICATION). THE BLOCK CAN ALSO CONTAIN DECLARATIONS OF CONSTANTS, TYPES, VARIABLES,PROCEDURES, AND FUNCTIONS; THESE DECLARATIONS MUST PRECEDE THE STATEMENT PART OF THE BLOCK. THE UNITHEADING SPECIFIES THE UNIT'S NAME. IT CONSISTS OF THE RESERVED WORD UNIT, FOLLOWED BY A VALID IDENTIFIER,FOLLOWED BY A SEMICOLON. FOR APPLICATIONS DEVELOPED USING BORLAND TOOLS, THE IDENTIFIER MUST MATCHTHE UNIT FILE NAME. THUS, THE UNIT HEADING UNIT MAINFORM; WOULD OCCUR IN A SOURCE FILE CALLEDMAINFORM.PAS, AND THE FILE CONTAINING THE COMPILED UNIT WOULD BE MAINFORM.DCU OR MAINFORM.DPU. UNIT NAMESMUST BE UNIQUE WITHIN A PROJECT. EVEN IF THEIR UNIT FILES ARE IN DIFFERENT DIRECTORIES, TWO UNITSWITH THE SAME NAME CANNOT BE USED IN A SINGLE PROGRAM. THE INTERFACE SECTION OF A UNIT BEGINS WITH THERESERVED WORD INTERFACE AND CONTINUES UNTIL THE BEGINNING OF THE IMPLEMENTATION SECTION. THEINTERFACE SECTION DECLARES CONSTANTS, TYPES, VARIABLES, PROCEDURES, AND FUNCTIONS THAT ARE AVAILABLE TOCLIENTS--THAT IS, TO OTHER UNITS OR PROGRAMS THAT

WISH TO USE ELEMENTS FROM THIS INTERFACE SECTION.THESE ENTITIES ARE CALLED PUBLIC BECAUSE A CLIENT CAN ACCESS THEM AS IF THEY WERE DECLARED IN THECLIENT ITSELF. THE INTERFACE DECLARATION OF A PROCEDURE OR FUNCTION INCLUDES ONLY THE ROUTINE'SHEADING. THE BLOCK OF THE PROCEDURE OR FUNCTION FOLLOWS IN THE IMPLEMENTATION SECTION. THUS PROCEDURE ANDFUNCTION DECLARATIONS IN THE INTERFACE SECTION WORK LIKE FORWARD DECLARATIONS, ALTHOUGH THE FORWARDDIRECTIVE ISN'T USED. THE INTERFACE DECLARATION FOR A CLASS MUST INCLUDE DECLARATIONS FOR ALL CLASSMEMBERS. THE INTERFACE SECTION CAN INCLUDE ITS OWN USES CLAUSE, WHICH MUST APPEAR IMMEDIATELY AFTERTHE WORD INTERFACE. FOR INFORMATION ABOUT THE USES CLAUSE, SEE UNIT REFERENCES AND THE USES CLAUSE.THE IMPLEMENTATION SECTION OF A UNIT BEGINS WITH THE RESERVED WORD IMPLEMENTATION AND CONTINUESUNTIL THE BEGINNING OF THE INITIALIZATION SECTION OR, IF THERE IS NO INITIALIZATION SECTION, UNTIL THEEND OF THE UNIT. THE IMPLEMENTATION SECTION DEFINES PROCEDURES AND FUNCTIONS THAT ARE DECLARED INTHE INTERFACE SECTION. WITHIN THE IMPLEMENTATION SECTION, THESE PROCEDURES AND FUNCTIONS MAY BEDEFINED AND CALLED IN ANY ORDER. YOU CAN OMIT PARAMETER LISTS FROM PUBLIC PROCEDURE AND FUNCTION HEADINGSWHEN YOU DEFINE THEM IN THE IMPLEMENTATION SECTION; BUT IF YOU INCLUDE A PARAMETER LIST, IT MUSTMATCH THE DECLARATION IN THE INTERFACE SECTION EXACTLY. IN ADDITION TO DEFINITIONS OF PUBLIC PROCEDURESAND FUNCTIONS, THE IMPLEMENTATION SECTION CAN DECLARE CONSTANTS, TYPES (INCLUDING CLASSES),VARIABLES, PROCEDURES, AND FUNCTIONS THAT ARE PRIVATE TO THE UNIT--THAT IS, INACCESSIBLE TO CLIENTS. THEIMPLEMENTATION SECTION CAN INCLUDE ITS OWN USES CLAUSE, WHICH MUST APPEAR IMMEDIATELY AFTER THE WORDIMPLEMENTATION. FOR INFORMATION ABOUT THE USES CLAUSE, SEE UNIT REFERENCES AND THE USES CLAUSE. THEINITIALIZATION SECTION IS OPTIONAL. IT BEGINS

WITH THE RESERVED WORD INITIALIZATION AND CONTINUESUNTIL THE BEGINNING OF THE FINALIZATION SECTION OR, IF THERE IS NO FINALIZATION SECTION, UNTIL THEEND OF THE UNIT. THE INITIALIZATION SECTION CONTAINS STATEMENTS THAT ARE EXECUTED, IN THE ORDER INWHICH THEY APPEAR, ON PROGRAM START-UP. SO, FOR EXAMPLE, IF YOU HAVE DEFINED DATA STRUCTURES THAT NEEDTO BE INITIALIZED, YOU CAN DO THIS IN THE INITIALIZATION SECTION. FOR UNITS IN THE INTERFACE USESLIST, THE INITIALIZATION SECTIONS OF UNITS USED BY A CLIENT ARE EXECUTED IN THE ORDER IN WHICH THEUNITS APPEAR IN THE CLIENT'S USES CLAUSE. THE FINALIZATION SECTION IS OPTIONAL AND CAN APPEAR ONLY INUNITS THAT HAVE AN INITIALIZATION SECTION. THE FINALIZATION SECTION BEGINS WITH THE RESERVED WORDFINALIZATION AND CONTINUES UNTIL THE END OF THE UNIT. IT CONTAINS STATEMENTS THAT ARE EXECUTED WHENTHE MAIN PROGRAM TERMINATES (UNLESS THE HALT PROCEDURE IS USED TO TERMINATE THE PROGRAM). USE THEFINALIZATION SECTION TO FREE RESOURCES THAT ARE ALLOCATED IN THE INITIALIZATION SECTION.FINALIZATION SECTIONS ARE EXECUTED IN THE OPPOSITE ORDER FROM INITIALIZATIONS. FOR EXAMPLE, IF YOURAPPLICATION INITIALIZES UNITS A, B, AND C, IN THAT ORDER, IT WILL FINALIZE THEM IN THE ORDER C, B, AND A.ONCE A UNIT'S INITIALIZATION CODE STARTS TO EXECUTE, THE CORRESPONDING FINALIZATION SECTION ISGUARANTEED TO EXECUTE WHEN THE APPLICATION SHUTS DOWN. THE FINALIZATION SECTION MUST THEREFORE BE ABLE TOHANDLE INCOMPLETELY INITIALIZED DATA, SINCE, IF A RUNTIME ERROR OCCURS, THE INITIALIZATION CODEMIGHT NOT EXECUTE COMPLETELY. A USES CLAUSE LISTS UNITS USED BY THE PROGRAM, LIBRARY, OR UNIT INWHICH THE CLAUSE APPEARS. (FOR INFORMATION ABOUT LIBRARIES, SEE LIBRARIES AND PACKAGES). A USES CLAUSECAN OCCUR IN THE PROJECT FILE FOR A PROGRAM OR

LIBRARY, THE INTERFACE SECTION OF A UNIT, AND THEIMPLEMENTATION SECTION OF A UNIT. MOST PROJECT FILES CONTAIN A USES CLAUSE, AS DO THE INTERFACESECTIONS OF MOST UNITS. THE IMPLEMENTATION SECTION OF A UNIT CAN CONTAIN ITS OWN USES CLAUSE AS WELL. THESYSTEM UNIT AND THE SYSINIT UNIT ARE USED AUTOMATICALLY BY EVERY APPLICATION AND CANNOT BE LISTEDEXPLICITLY IN THE USES CLAUSE. (SYSTEM IMPLEMENTS ROUTINES FOR FILE I/O, STRING HANDLING, FLOATINGPOINT OPERATIONS, DYNAMIC MEMORY ALLOCATION, AND SO FORTH.) OTHER STANDARD LIBRARY UNITS, SUCH ASSYSUTILS, MUST BE INCLUDED IN THE USES CLAUSE. IN MOST CASES, ALL NECESSARY UNITS ARE PLACED IN THE USESCLAUSE WHEN YOUR PROJECT GENERATES AND MAINTAINS A SOURCE FILE. IN UNIT DECLARATIONS AND USESCLAUSES (ON LINUX PARTICULARLY), UNIT NAMES MUST MATCH THE FILE NAMES IN CASE. IN OTHER CONTEXTS (SUCH ASQUALIFIED IDENTIFIERS), UNIT NAMES ARE CASE INSENSITIVE. TO AVOID PROBLEMS WITH UNIT REFERENCES,REFER TO THE UNIT SOURCE FILE EXPLICITLY: USES MYUNIT IN "MYUNIT.PAS"; IF SUCH AN EXPLICITREFERENCE APPEARS IN THE PROJECT FILE, OTHER SOURCE FILES CAN REFER TO THE UNIT WITH A SIMPLE USES CLAUSETHAT DOES NOT NEED TO MATCH CASE: USES MYUNIT; FOR MORE INFORMATION ABOUT THE PLACEMENT ANDCONTENT OF THE USES CLAUSE, SEE MULTIPLE AND INDIRECT UNIT REFERENCES AND CIRCULAR UNIT REFERENCES. ALSOSEE THE SYNTAX OF A USES CLAUSE. A USES CLAUSE CONSISTS OF THE RESERVED WORD USES, FOLLOWED BY ONEOR MORE COMMA-DELIMITED UNIT NAMES, FOLLOWED BY A SEMICOLON. EXAMPLES: USES FORMS, MAIN;USES FORMS, MAIN; USES WINDOWS, MESSAGES, SYSUTILS, STRINGS, CLASSES, UNIT2, MYUNIT; USESSYSUTILS, TYPES, CLASSES, QGRAPHICS, QCONTROLS, QFORMS, QDIALOGS; IN THE USES CLAUSE OF APROGRAM OR LIBRARY, ANY UNIT NAME MAY BE FOLLOWED BY THE RESERVED WORD IN AND THE NAME OF A SOURCEFILE, WITH OR WITHOUT A DIRECTORY PATH, IN SINGLE QUOTATION MARKS; DIRECTORY PATHS CAN BE ABSOLUTE ORRELATIVE. EXAMPLES: USES {THIS EXAMPLE IS WINDOWS-SPECIFIC} WINDOWS, MESSAGES,SYSUTILS, STRINGS IN 'C:\CLASSES\STRINGS.PAS',

CLASSES; USES {THIS IS A LINUX EXAMPLE} QFORMS,MAIN, EXTRA IN '../EXTRA/EXTRA.PAS'; INCLUDE IN ... AFTER A UNIT NAME WHEN YOU NEED TOSPECIFY THE UNIT'S SOURCE FILE. SINCE THE IDE EXPECTS UNIT NAMES TO MATCH THE NAMES OF THE SOURCEFILES IN WHICH THEY RESIDE, THERE IS USUALLY NO REASON TO DO THIS. USING IN IS NECESSARY ONLY WHEN THELOCATION OF THE SOURCE FILE IS UNCLEAR, FOR EXAMPLE WHEN YOU HAVE USED A SOURCE FILE THAT IS IN ADIFFERENT DIRECTORY FROM THE PROJECT FILE, AND THAT DIRECTORY IS NOT IN THE COMPILER'S SEARCH PATH.DIFFERENT DIRECTORIES IN THE COMPILER'S SEARCH PATH HAVE IDENTICALLY NAMED UNITS. YOU ARE COMPILING ACONSOLE APPLICATION FROM THE COMMAND LINE, AND YOU HAVE NAMED A UNIT WITH AN IDENTIFIER THAT DOESN'TMATCH THE NAME OF ITS SOURCE FILE. THE COMPILER ALSO RELIES ON THE IN ... CONSTRUCTION TO DETERMINEWHICH UNITS ARE PART OF A PROJECT. ONLY UNITS THAT APPEAR IN A PROJECT (.DPR) FILE'S USES CLAUSEFOLLOWED BY IN AND A FILE NAME ARE CONSIDERED TO BE PART OF THE PROJECT; OTHER UNITS IN THE USESCLAUSE ARE USED BY THE PROJECT WITHOUT BELONGING TO IT. THIS DISTINCTION HAS NO EFFECT ON COMPILATION,BUT IT AFFECTS IDE TOOLS LIKE THE PROJECT MANAGER AND PROJECT BROWSER. IN THE USES CLAUSE OF A UNIT,YOU CANNOT USE IN TO TELL THE COMPILER WHERE TO FIND A SOURCE FILE. EVERY UNIT MUST BE IN THECOMPILER'S SEARCH PATH. MOREOVER, UNIT NAMES MUST MATCH THE NAMES OF THEIR SOURCE FILES. PARAMETERSARE TRANSFERRED TO PROCEDURES AND FUNCTIONS VIA CPU REGISTERS OR THE STACK, DEPENDING ON THEROUTINE'S CALLING CONVENTION. FOR INFORMATION ABOUT CALLING CONVENTIONS, SEE CALLING CONVENTIONS. VARIABLE(VAR) PARAMETERS ARE ALWAYS PASSED BY REFERENCE, AS 32-BIT POINTERS THAT POINT TO THE ACTUAL STORAGELOCATION. VALUE AND CONSTANT (CONST) PARAMETERS ARE PASSED BY VALUE OR BY REFERENCE, DEPENDING ONTHE TYPE AND SIZE OF THE PARAMETER: AN ORDINAL PARAMETER IS PASSED AS AN 8-BIT, 16-BIT, 32-BIT,

OR64-BIT VALUE, USING THE SAME FORMAT AS A VARIABLE OF THE CORRESPONDING TYPE. A REAL PARAMETER ISALWAYS PASSED ON THE STACK. A SINGLE PARAMETER OCCUPIES 4 BYTES, AND A DOUBLE, COMP, OR CURRENCYPARAMETER OCCUPIES 8 BYTES. A REAL48 OCCUPIES 8 BYTES, WITH THE REAL48 VALUE STORED IN THE LOWER 6 BYTES. ANEXTENDED OCCUPIES 12 BYTES, WITH THE EXTENDED VALUE STORED IN THE LOWER 10 BYTES. A SHORT-STRINGPARAMETER IS PASSED AS A 32-BIT POINTER TO A SHORT STRING. A LONG-STRING OR DYNAMIC-ARRAY PARAMETER ISPASSED AS A 32-BIT POINTER TO THE DYNAMIC MEMORY BLOCK ALLOCATED FOR THE LONG STRING. THE VALUE NILIS PASSED FOR AN EMPTY LONG STRING. A POINTER, CLASS, CLASS-REFERENCE, OR PROCEDURE-POINTERPARAMETER IS PASSED AS A 32-BIT POINTER. A METHOD POINTER IS PASSED ON THE STACK AS TWO 32-BIT POINTERS.THE INSTANCE POINTER IS PUSHED BEFORE THE METHOD POINTER SO THAT THE METHOD POINTER OCCUPIES THELOWEST ADDRESS. UNDER THE REGISTER AND PASCAL CONVENTIONS, A VARIANT PARAMETER IS PASSED AS A 32-BITPOINTER TO A VARIANT VALUE. SETS, RECORDS, AND STATIC ARRAYS OF 1, 2, OR 4 BYTES ARE PASSED AS 8-BIT,16-BIT, AND 32-BIT VALUES. LARGER SETS, RECORDS, AND STATIC ARRAYS ARE PASSED AS 32-BIT POINTERS TOTHE VALUE. AN EXCEPTION TO THIS RULE IS THAT RECORDS ARE ALWAYS PASSED DIRECTLY ON THE STACK UNDER THECDECL, STDCALL, AND SAFECALL CONVENTIONS; THE SIZE OF A RECORD PASSED THIS WAY IS ROUNDED UPWARD TOTHE NEAREST DOUBLE-WORD BOUNDARY. AN OPEN-ARRAY PARAMETER IS PASSED AS TWO 32-BIT VALUES. THE FIRSTVALUE IS A POINTER TO THE ARRAY DATA, AND THE SECOND VALUE IS ONE LESS THAN THE NUMBER OF ELEMENTSIN THE ARRAY. WHEN TWO PARAMETERS ARE PASSED ON THE STACK, EACH PARAMETER OCCUPIES A MULTIPLE OF 4BYTES (A WHOLE NUMBER OF DOUBLE WORDS). FOR AN 8-BIT OR 16-BIT PARAMETER, EVEN THOUGH THE PARAMETER

OCCUPIES ONLY A BYTE OR A WORD, IT IS PASSED AS A DOUBLE WORD. THE CONTENTS OF THE UNUSED PARTS OFTHE DOUBLE WORD ARE UNDEFINED. UNDER THE PASCAL, CDECL, STDCALL AND SAFECALL CONVENTIONS, ALLPARAMETERS ARE PASSED ON THE STACK. UNDER THE PASCAL CONVENTION, PARAMETERS ARE PUSHED IN THE ORDER OF THEIRDECLARATION (LEFT-TO-RIGHT), SO THAT THE FIRST PARAMETER ENDS UP AT THE HIGHEST ADDRESS AND THELAST PARAMETER ENDS UP AT THE LOWEST ADDRESS. UNDER THE CDECL, STDCALL, AND SAFECALL CONVENTIONS,PARAMETERS ARE PUSHED IN REVERSE ORDER OF DECLARATION (RIGHT-TO-LEFT), SO THAT THE FIRST PARAMETER ENDSUP AT THE LOWEST ADDRESS AND THE LAST PARAMETER ENDS UP AT THE HIGHEST ADDRESS. UNDER THE REGISTERCONVENTION, UP TO THREE PARAMETERS ARE PASSED IN CPU REGISTERS, AND THE REST (IF ANY) ARE PASSED ONTHE STACK. THE PARAMETERS ARE PASSED IN ORDER OF DECLARATION (AS WITH THE PASCAL CONVENTION), AND THEFIRST THREE PARAMETERS THAT QUALIFY ARE PASSED IN THE EAX, EDX, AND ECX REGISTERS, IN THAT ORDER.REAL, METHOD-POINTER, VARIANT, INT64, AND STRUCTURED TYPES) DO NOT QUALIFY AS REGISTER PARAMETERS, BUTALL OTHER PARAMETERS DO. IF MORE THAN THREE PARAMETERS QUALIFY AS REGISTER PARAMETERS, THE FIRSTTHREE ARE PASSED IN EAX, EDX, AND ECX, AND THE REMAINING PARAMETERS ARE PUSHED ONTO THE STACK IN ORDEROF DECLARATION. FOR EXAMPLE, GIVEN THE DECLARATION PROCEDURE TEST(A: INTEGER; VAR B: CHAR; C:DOUBLE; CONST D: STRING; E: POINTER); A CALL TO TEST PASSES A IN EAX AS A 32-BIT INTEGER, B IN EDX AS APOINTER TO A CHAR, AND D IN ECX AS A POINTER TO A LONG-STRING MEMORY BLOCK; C AND E ARE PUSHED ONTOTHE STACK AS TWO DOUBLE-WORDS AND A 32-BIT POINTER, IN THAT ORDER. REGISTER SAVING CONVENTIONSPROCEDURES AND FUNCTIONS MUST PRESERVE THE EBX, ESI, EDI, AND EBP REGISTERS, BUT CAN MODIFY THEEAX, EDX, AND ECX REGISTERS. WHEN IMPLEMENTING A CONSTRUCTOR OR DESTRUCTOR IN ASSEMBLER, BE SURE TO

PRESERVE THE DL REGISTER. PROCEDURES AND FUNCTIONS ARE INVOKED WITH THE ASSUMPTION THAT THE CPU'SDIRECTION FLAG IS CLEARED (CORRESPONDING TO A CLD INSTRUCTION) AND MUST RETURN WITH THE DIRECTIONFLAG CLEARED. NOTE DELPHI LANGUAGE PROCEDURES AND FUNCTIONS ARE GENERALLY INVOKED WITH THEASSUMPTION THAT THE FPU STACK IS EMPTY: THE COMPILER TRIES TO USE ALL EIGHT FPU STACK ENTRIES WHEN ITGENERATES CODE. WHEN WORKING WITH THE MMX AND XMM INSTRUCTIONS, BE SURE TO PRESERVE THE VALUES OF THE XMMAND MM REGISTERS. DELPHI FUNCTIONS ARE INVOKED WITH THE ASSUMPTION THAT THE X87 FPU DATA REGISTERSARE AVAILABLE FOR USE BY X87 FLOATING POINT INSTRUCTIONS. THAT IS, THE COMPILER ASSUMES THAT THEEMMS/FEMMS INSTRUCTION HAS BEEN CALLED AFTER MMX OPERATIONS. DELPHI FUNCTIONS DO NOT MAKE ANYASSUMPTIONS ABOUT THE STATE AND CONTENT OF XMM REGISTERS. THEY DO NOT GUARANTEE THAT THE CONTENT OF XMMREGISTERS IS UNCHANGED. BLAVATSKY, HELENA PETROVNA (1831-91), RUSSIAN-BORN AMERICAN LEADER OF THEMODERN RELIGIOPHILOSOPHICAL SYSTEM KNOWN AS THEOSOPHY. ORIGINALLY NAMED HELENA HAHN, SHE WAS BORN OFGERMAN PARENTS IN YEKATERINOSLAV (NOW DNIPROPETROVS'K, UKRAINE). AT THE AGE OF 16 SHE MARRIED A MUCHOLDER MAN BUT LEFT HIM AFTER A FEW MONTHS. SHE SPENT THE NEXT 20 YEARS TRAVELING IN EUROPE, ASIA,AND THE UNITED STATES, LATER CLAIMING TO HAVE STUDIED FOR SEVEN YEARS UNDER HINDU MAHATMAS (MASTERS)IN THE EAST. AFTER A NARROW ESCAPE FROM DROWNING AT SEA, SHE TURNED TO SPIRITUALISM AND CLAIMED TOPOSSESS PSYCHIC POWERS. IN 1873 MADAME BLAVATSKY, AS SHE WAS ALWAYS KNOWN, WENT TO NEW YORK CITY.WITHIN TWO YEARS SHE WAS TO BECOME ONE OF THE FOUNDERSUAND EVENTUALLY THE CENTRAL FIGUREUOF THETHEOSOPHICAL SOCIETY, A SMALL BUT ACTIVE INTERNATIONAL GROUP OF OCCULTISTS WHO BELIEVED IN REINCARNATIONAS THE NECESSARY PATH TO THE ULTIMATE, INEVITABLE PURIFICATION OF HUMANITY. SHE BECAME AN AMERICANCITIZEN, BUT IN 1878 SHE ESTABLISHED A NEW

HEADQUARTERS IN INDIA. SOON SHE WAS FACED WITH DISSENSION,CHARGES OF CHICANERY AND PLAGIARISM, AND CONSIDERABLE NOTORIETY. SHE MAINTAINED TO THE END OF HERLIFE, HOWEVER, THAT THE MAHATMAS HAD ACTUALLY BEEN ABLE TO PASS ON TO HER THEIR OWN UNCOMMONLYDEVELOPED SPIRITUAL STATE. BLAVATSKY'S MAJOR WORKS, ISIS UNVEILED (1877) AND THE SECRET DOCTRINE (1888),BECAME THE TEXTBOOKS OF THE THEOSOPHICAL SOCIETY. THEOSOPHY (GREEK THEOS, "GOD"; SOPHOS, "WISE"),DESIGNATION FOR ANY RELIGIOPHILOSOPHICAL SYSTEM PURPORTING TO FURNISH KNOWLEDGE OF GOD, AND OF THEUNIVERSE IN RELATION TO GOD, BY MEANS OF DIRECT MYSTICAL INTUITION, PHILOSOPHICAL INQUIRY, OR BOTH.PRECURSORS OF THEOSOPHY EARLY EXAMPLES OF THEOSOPHIC THOUGHT ARE FOUND IN THE SANSKRITMETAPHYSICAL TREATISES KNOWN AS THE UPANISHADS. HINDU PHILOSOPHY SUBSEQUENT TO THE COMPOSITION OF THEUPANISHADS (ABOUT THE 8TH CENTURY BC) HAS BEEN PREDOMINANTLY THEOSOPHIC IN TONE. INDIAN THOUGHTPROBABLY HAD SOME INFLUENCE IN PERSIA, WHERE THEOSOPHIC SPECULATION BECAME POPULAR AFTER THE ARAB CONQUESTIN THE FIRST HALF OF THE 7TH CENTURY AD. IN CHINA, BOTH THE I CHING (BOOK OF CHANGES), ONE OF THESO-CALLED FIVE CLASSICS OF CONFUCIANISM, AND THE TAO-TE CHING (CLASSIC OF THE WAY AND ITS POWER), AMAJOR TREATISE OF TAOISM, CONTAIN THEOSOPHIC ELEMENTS. IN THE WEST SUCH SYSTEMS OF THOUGHT ASNEOPLATONISM AND GNOSTICISM CONTAIN THEOSOPHIC ELEMENTS. ELEMENTS SIMILAR TO THOSE OF NEOPLATONISM ANDGNOSTICISM REAPPEAR IN THE CABALA, A MYSTICAL INTERPRETATION OF SCRIPTURES CURRENT AMONG THE JEWS OFEUROPE BETWEEN THE 12TH AND 16TH CENTURIES. IN THE MIDDLE AGES, THEOSOPHIC TEACHINGS WERE EXPOUNDED BYTHE GERMAN MYSTICS AND PREACHERS MEISTER ECKHART AND JOHANNES TAULER AND BY THE SWISS PHYSICIAN ANDALCHEMIST PHILIPPUS AUREOLUS PARACELSUS, AND, IN LATER PERIODS, BY THE GERMAN MYSTIC JAKOB BOEHMEAND THE FLEMISH PHYSICIAN AND CHEMIST JAN

BAPTISTA VAN HELMONT. THE THEOSOPHICAL SOCIETY THETERM THEOSOPHY HAS BEEN EMPLOYED WITH PARTICULAR REFERENCE TO A SYSTEM OF OCCULT PHILOSOPHY SETFORTH BY HELENA PETROVNA BLAVATSKY AND HER FOLLOWERS IN THE THEOSOPHICAL SOCIETY, WHICH SHE HELPEDORGANIZE IN NEW YORK CITY IN 1875. SHE MAINTAINED THAT SHE HAD RECEIVED HER DOCTRINES FROM ORIENTALRELIGIOUS TEACHERS WHO HAD REACHED A HIGHER PLANE OF EXISTENCE THAN THAT OF OTHER MORTALS. ACCORDING TOHER TEACHING, GOD IS INFINITE, ABSOLUTE, AND UNKNOWABLE (AN ATTRIBUTE APPARENTLY INCOMPATIBLE WITHTHE CLAIM IMPLICIT IN THE TERM THEOSOPHY). THE DEITY IS ALSO SAID TO BE THE SOURCE OF BOTH SPIRIT ANDMATTER. THROUGH THE OPERATION OF AN IMMUTABLE LAW, SPIRIT IS SAID TO DESCEND INTO MATTER, ANDMATTER TO ASCEND INTO SPIRIT, BY CYCLICAL ACTION. IN ITS PSYCHOLOGICAL APPLICATION, BLAVATSKY'S DOCTRINEREPRESENTS ALL SOULS AS BEING THE SAME IN ESSENCE, ALTHOUGH DIFFERING IN DEGREES OF DEVELOPMENT. THEMORE ADVANCED SOULS ARE SAID TO BE THE NATURAL GUARDIANS OF THE LESS DEVELOPED. HUMAN BEINGS AREPRESENTED AS COMPLEX, WITH BOTH A HIGHER AND LOWER NATURE. THE HIGHER (COMPRISING MIND, SOUL, ANDSPIRIT) HAS BEEN POLLUTED BY THE LOWER (PHYSICAL AND OTHER) AND MUST BE PURIFIED BEFORE IT CANCOMPLETELY RETURN TO THE DIVINE. PURIFICATION IS THOUGHT TO TAKE PLACE THROUGH A SERIES OF INCARNATIONS.CABALA (HEBREW, "RECEIVED TRADITION"), GENERICALLY, JEWISH MYSTICISM IN ALL ITS FORMS;SPECIFICALLY, THE ESOTERIC THEOSOPHY THAT CRYSTALLIZED IN 13TH-CENTURY SPAIN AND PROVENCE, FRANCE, AROUND SEFERHA-ZOHAR (THE BOOK OF SPLENDOR), REFERRED TO AS THE ZOHAR, AND GENERATED ALL LATER MYSTICALMOVEMENTS IN JUDAISM. SEE MYSTICISM; THEOSOPHY. THE EARLIEST KNOWN FORM OF JEWISH MYSTICISM DATES FROM THEFIRST CENTURIES AD AND IS A VARIANT ON THE PREVAILING HELLENISTIC ASTRAL MYSTICISM, IN WHICH THEADEPT, THROUGH MEDITATION AND THE USE OF MAGIC FORMULAS, JOURNEYS ECSTATICALLY THROUGH AND

BEYOND THESEVEN ASTRAL SPHERES. IN THE JEWISH VERSION, THE ADEPT SEEKS AN ECSTATIC VERSION OF GOD'S THRONE, THECHARIOT (MERKAVA) BEHELD BY EZEKIEL (SEE EZEKIEL 1). THE MEDIEVAL PERIOD MEDIEVAL SPANISHCABALA, THE MOST IMPORTANT FORM OF JEWISH MYSTICISM, IS LESS CONCERNED WITH ECSTATIC EXPERIENCE THANWITH ESOTERIC KNOWLEDGE ABOUT THE NATURE OF THE DIVINE WORLD AND ITS HIDDEN CONNECTIONS WITH THEWORLD OF CREATION. MEDIEVAL CABALA IS A THEOSOPHICAL SYSTEM THAT DRAWS ON NEOPLATONISM AND GNOSTICISMAND IS EXPRESSED IN SYMBOLIC LANGUAGE. THE SYSTEM IS MOST FULLY ARTICULATED IN THE ZOHAR, WRITTENBETWEEN 1280 AND 1286 BY THE SPANISH CABALIST MOSES DE LEEN, BUT ATTRIBUTED TO THE 2ND-CENTURY RABBISIMEON BAR YOHAI. THE ZOHAR DEPICTS THE GODHEAD AS A DYNAMIC FLOW OF FORCE COMPOSED OF NUMEROUSASPECTS. ABOVE AND BEYOND ALL HUMAN CONTEMPLATION IS GOD AS HE IS IN HIMSELF, THE UNKNOWABLE, IMMUTABLE ENSOF (INFINITE). OTHER ASPECTS OR ATTRIBUTES, KNOWABLE THROUGH GOD'S RELATION TO THE CREATED WORLD,EMANATE (SEE EMANATION) FROM EN SOF IN A CONFIGURATION OF TEN SEFIROT (REALMS OR PLANES), THROUGHWHICH THE DIVINE POWER FURTHER RADIATES TO CREATE THE COSMOS. ZOHARIC THEOSOPHY CONCENTRATES ON THENATURE AND INTERACTION OF THE TEN SEFIROT AS SYMBOLS OF THE INNER LIFE AND PROCESSES OF THE GODHEAD.BECAUSE THE SEFIROT ARE ALSO ARCHETYPES FOR EVERYTHING IN THE WORLD OF CREATION, AN UNDERSTANDING OFTHEIR WORKINGS CAN ILLUMINATE THE INNER WORKINGS OF THE COSMOS AND OF HISTORY. THE ZOHAR THEREBYPROVIDES A COSMIC-SYMBOLIC INTERPRETATION OF JUDAISM AND OF THE HISTORY OF ISRAEL IN WHICH THE TORAH ANDCOMMANDMENTS, AS WELL AS ISRAEL'S LIFE IN EXILE, BECOME SYMBOLS FOR EVENTS AND PROCESSES IN THEINNER LIFE OF GOD. THUS INTERPRETED, THE PROPER OBSERVANCE OF THE COMMANDMENTS ASSUMES A COSMICSIGNIFICANCE. LURIANIC CABALA THIS COSMIC ASPECT OF THE ZOHAR IS DEVELOPED DRAMATICALLY AND WITHGREAT CONSEQUENCE IN 16TH-CENTURY LURIANIC CABALA (NAMED FOR ITS FORMULATOR, ISAAC BEN SOLOMON

LURIA).THE LURIANIC SYSTEM REPRESENTS A RESPONSE TO THE CATACLYSMIC EXPERIENCE OF JEWISH EXILES EXPELLEDFROM IBERIA IN THE 1490S; IT PROJECTS THIS EXPERIENCE ONTO THE DIVINE WORLD. IN THIS SYSTEM, THE EN SOFWITHDRAWS INTO ITSELF (TZIMTZUM) AT THE OUTSET OF CREATION, MAKING ROOM FOR THE WORLD, BUT ALSO FOREVIL. A COSMIC CATASTROPHE OCCURS DURING EMANATION WHEN VESSELS OF THE DIVINE LIGHT SHATTER AND THESPARKS ARE IMPRISONED IN THE WORLD IN SHARDS OF EVIL (QELIPPOT). THE HUMAN TASK, THROUGH PRAYER ANDPROPER OBSERVANCE OF THE COMMANDMENTS, BECOMES NOTHING LESS THAN THE REDEMPTION (TIQQUN) OF THEWORLD AND THE REUNIFICATION OF THE GODHEAD. THE CABALA WAS THUS TRANSFORMED INTO A POPULAR MESSIANICMOVEMENT, WHICH LATER GENERATED SABBATIAN MESSIANISM AND 18TH-CENTURY POLISH HASIDISM (SEE HASIDIM;SABBATAI ZEVI). TEMPERED, HOWEVER, BY A DROP IN WORLD COFFEE PRICES IN THE MID- AND LATE1950S. INFLATION CONTINUED, PRODDING SOCIAL UNREST THAT RESULTED IN FREQUENT STRIKES AND RIOTS BYWORKERS AND STUDENTS. JANIO DA SILVA QUADROS, FORMER GOVERNOR OF SAO PAULO, BECAME PRESIDENT OFBRAZIL IN JANUARY 1961 AND IMMEDIATELY INITIATED A PROGRAM OF RIGOROUS ECONOMIES. ALL GOVERNMENTALMINISTRIES WERE ORDERED TO REDUCE EXPENDITURES BY 30 PERCENT, AND SOME CIVIL-SERVICE EMPLOYEES WEREDISMISSED. QUADROS ALSO PROPOSED TO ELIMINATE THE CORRUPTION ALLEGED TO HAVE FLOURISHED DURING THEKUBITSCHEK ADMINISTRATION. PRESIDENT QUADROS SUDDENLY RESIGNED HIS OFFICE IN AUGUST, GIVING NOEXPLANATION, AND REFERRING ONLY TO THE OFORCES OF REACTION THAT HAD BLOCKED HIS EFFORTS. MILITARYLEADERS EXPRESSED OPPOSITION TO THE ASSUMPTION OF OFFICE BY VICE PRESIDENT JOAO BELCHOIR MARQUESGOULART, MAINTAINING THAT HE WAS SYMPATHETIC TO THE COMMUNIST REGIME OF FIDEL CASTRO IN CUBA. ACOMPROMISE WAS REACHED, HOWEVER, WHEN THE BRAZILIAN LEGISLATURE AMENDED THE CONSTITUTION IN ORDER TOSTRIP THE PRESIDENCY OF MOST POWERS; EXECUTIVE AUTHORITY WAS VESTED IN A PRIME MINISTER ANDCABINET WHO WERE RESPONSIBLE TO THE LEGISLATURE. GOULART WAS INSTALLED IN OFFICE IN SEPTEMBER 1961.

A YEAR LATER, GOULART PRECIPITATED A CABINET CRISIS WITH A REQUEST FOR A NATIONAL PLEBISCITE TOMEASURE SUPPORT FOR A RETURN TO A PRESIDENTIAL FORM OF GOVERNMENT. THE PLEBISCITE WAS HELD AND THEPROPOSAL APPROVED; IN JANUARY 1963, THE LEGISLATURE ENACTED THE CHANGE INTO LAW. LATER THAT YEARGOULART PRESSED STRONGLY FOR LEGISLATIVE APPROVAL OF A PROGRAM OF BASIC REFORMS, AND EARLY IN1964 HE SIGNED DECREES SETTING LOW-RENT CONTROLS, NATIONALIZING PETROLEUM REFINERIES, EXPROPRIATINGUNUSED LANDS, AND LIMITING EXPORT OF PROFITS. THE MEASURES SEEMED ONLY TO AGGRAVATE THE NATION'SCHRONIC INFLATION. ON MARCH 31 GOULART WAS OVERTHROWN BY AN ARMY REVOLT AND FLED TO URUGUAY.GENERAL HUMBERTO CASTELO BRANCO, ARMY CHIEF OF STAFF, WAS ELECTED PRESIDENT. MILITARY GOVERNMENTTHE NEW REGIME, WITH EXTRAORDINARY POWERS UNDER THE INSTITUTIONAL ACT SIGNED IN APRIL,SUPPRESSED OPPOSITION, PARTICULARLY FROM THE LEFT, AND DEPRIVED SOME 300 PEOPLE OF POLITICAL RIGHTS. ITALSO ADOPTED MODERATE VERSIONS OF MANY REFORMS DEMANDED BY GOULART AND FOUGHT INFLATION WITH WAGECONTROLS, TIGHTENED TAX COLLECTIONS, AND OTHER MEASURES. A LAW PASSED IN 1965 CURBED CIVILLIBERTIES, INCREASED THE POWER OF THE NATIONAL GOVERNMENT, AND PROVIDED FOR CONGRESSIONAL ELECTION OF THEPRESIDENT AND VICE PRESIDENT. THE FORMER MINISTER OF WAR MARSHAL ARTUR DA COSTA E SILVA,CANDIDATE OF THE GOVERNMENT'S ARENA PARTY, WAS ELECTED PRESIDENT IN 1966. THE BRAZILIAN DEMOCRATIC MOVEMENT(MDB), THE ONLY LEGAL OPPOSITION PARTY, HAD REFUSED TO ENTER A CANDIDATE IN PROTEST AGAINST THEGOVERNMENT'S DISFRANCHISEMENT OF ITS MOST CHALLENGING OPPONENTS. ALSO IN 1966 ARENA WON THE NATIONALAND STATE LEGISLATIVE ELECTIONS. PRESIDENT COSTA HEADED A MILITARILY ORIENTED GOVERNMENT THAT WASCONCERNED PRIMARILY WITH ECONOMIC DEVELOPMENT. ALTHOUGH 1968 WAS MARKED BY ANTIGOVERNMENTACTIVITIES, INCLUDING STUDENT RIOTS, THE ECONOMY GAINED MOMENTUM. IN DECEMBER COSTA ASSUMED UNLIMITEDPOWERS, WHICH RESULTED IN POLITICAL PURGES,

ECONOMIC CURBS, AND CENSORSHIP. IN AUGUST 1969 HE WASINCAPACITATED BY A STROKE, AND IN OCTOBER THE MILITARY CHOSE AS HIS SUCCESSOR GENERAL EMILIO GARRASTAZMEDICI; CONGRESS ELECTED HIM PRESIDENT. THE MEDICI REGIME INTENSIFIED REPRESSION, AND REVOLUTIONARYGROUPS BECAME MORE ACTIVE. AS THE GOVERNMENT ENCOURAGED ECONOMICGROWTH AND DEVELOPMENT OF THEVAST INTERIOR REGIONS, THE ECONOMY WAS PLAGUED BY HIGH ENERGY COSTS, RUNAWAY INFLATION, AND A LARGEBALANCE-OF-PAYMENTS DEFICIT. THE ROMAN CATHOLIC CLERGY BECAME INCREASINGLY CRITICAL OF THEGOVERNMENT'S FAILURE TO IMPROVE THE CONDITION OF THE POOR. IN 1974 GENERAL ERNEST GEISEL, THE PRESIDENT OFPETROBRAS, THE NATIONAL OIL MONOPOLY, BECAME PRESIDENT. AT FIRST HE FOLLOWED RELATIVELY LIBERALPOLICIES, RELAXING PRESS CENSORSHIP AND ALLOWING OPPOSITION PARTIES CONSIDERABLE FREEDOM, BUT IN1976 AND 1977 CONTROLS WERE TIGHTENED AGAIN JUST BEFORE THE ELECTION OF JOAO BAPTISTA DE OLIVEIRAFIGUEIREDO, WHO SUCCEEDED GEISEL IN 1979. RESTORATION OF CIVIL RULE IN 1985 TANCREDO NEVESWAS SELECTED AS BRAZIL'S FIRST CIVILIAN PRESIDENT IN 21 YEARS; HE DIED BEFORE TAKING OFFICE, ANDJOSE SARNEY BECAME PRESIDENT. FACED WITH RESURGENT INFLATION AND A HUGE FOREIGN DEBT, SARNEY IMPOSEDAN AUSTERITY PROGRAM THAT INCLUDED INTRODUCING A NEW UNIT OF CURRENCY. A NEW CONSTITUTIONPROVIDING FOR DIRECT PRESIDENTIAL ELECTIONS WAS ENACTED IN OCTOBER 1988, AND FERNANDO COLLOR DE MELLO, OFTHE CONSERVATIVE NATIONAL RECONSTRUCTION PARTY, WAS ELECTED PRESIDENT IN DECEMBER 1989. HISDRASTIC ANTI-INFLATION PROGRAM CONTRIBUTED TO BRAZIL'S WORST RECESSION IN TEN YEARS, AND ALLEGATIONSOF FINANCIAL CORRUPTION FURTHER ERODED HIS POPULARITY. IN JUNE 1992 BRAZIL WAS HOST TO MORE THAN100 WORLD LEADERS FOR THE UNITED NATIONS CONFERENCE ON ENVIRONMENT AND DEVELOPMENT, ALSO KNOWN ASTHE EARTH SUMMIT. IN SEPTEMBER COLLOR WAS IMPEACHED BY THE CHAMBER OF DEPUTIES, AND VICE PRESIDENTITAMAR FRANCO BECAME ACTING PRESIDENT. COLLOR

RESIGNED ON DECEMBER 29, JUST AS HIS SENATE TRIALWAS BEGINNING, AND FRANCO WAS THEN SWORN IN AS HIS SUCCESSOR. A PLAN TO RESTRUCTURE AND REDUCEBRAZIL'S FOREIGN DEBT WAS IMPLEMENTED IN APRIL 1994. IN MAY BRAZIL SIGNED THE TREATY OF TLATELOCO ANDJOINED OTHER LATIN AMERICAN AND CARIBBEAN NATIONS IN DECLARING ITSELF FREE OF NUCLEAR WEAPONS.FERNANDO HENRIQUE CARDOSO, A FORMER FINANCE MINISTER RESPONSIBLE FOR MUCH OF BRAZIL'S ECONOMICRECOVERY, WON THE NOVEMBER 1994 PRESIDENTIAL ELECTIONS, WINNING TWICE AS MANY VOTES AS HIS NEARESTCHALLENGER. IN DECEMBER 1994, FORMER PRESIDENT COLLOR WAS ACQUITTED OF CORRUPTION CHARGES BUTREMAINS BANNED FROM BRAZILIAN POLITICS UNTIL THE YEAR 2000. ON JANUARY 1, 1995, BRAZIL JOINEDARGENTINA, PARAGUAY, AND URUGUAY IN THE FORMATION OF THE SOUTHERN CONE COMMON MARKET (MERCOSUR). ALSO IN1995, BRAZIL LOOKED TOWARDS PRIVATE INVESTORS FOR FINANCIAL AND TECHNICAL ASSISTANCE WITH LARGEINFRASTRUCTURE PROJECTS SUCH AS THE DEVELOPMENT AND MAINTENANCE OF HIGHWAYS, TELEPHONE NETWORKS, ANDELECTRICITY-GENERATING FACILITIES. UNITED STATES OF AMERICA, POPULARLY REFERRED TO AS THE UNITEDSTATES OR AS AMERICA, A FEDERAL REPUBLIC ON THE CONTINENT OF NORTH AMERICA, CONSISTING OF 48CONTIGUOUS STATES AND THE NONCONTIGUOUS STATES OF ALASKA AND HAWAII. OUTLYING AREAS INCLUDE PUERTORICO, AMERICAN SAMOA, GUAM, AND THE VIRGIN ISLANDS OF THE UNITED STATES. THE CONTERMINOUS 48 STATESARE BOUNDED ON THE NORTH BY CANADA, ON THE EAST BY THE ATLANTIC OCEAN, ON THE SOUTH BY THE GULF OFMEXICO AND MEXICO, AND ON THE WEST BY THE PACIFIC OCEAN. THE NORTHERN BOUNDARY IS PARTLY FORMED BY THEGREAT LAKES AND THE SAINT LAWRENCE RIVER; THE SOUTHERN BOUNDARY IS PARTLY FORMED BY THE RIO GRANDE.NEW YORK CITY IS THE LARGEST CITY IN THE UNITED STATES. WASHINGTON, D.C., IS THE CAPITAL. THETOTAL AREA OF THE UNITED STATES (INCLUDING THE DISTRICT OF COLUMBIA) IS 9,666,861 SQ KM (3,732,396SQ MI), OF WHICH 1,593,438 SQ KM (615,230 SQ MI) ARE IN ALASKA AND 16,729 SQ KM (6459 SQ MI) ARE

INHAWAII. INLAND, COASTAL, AND GREAT LAKES BODIES OF WATER OCCUPY 507,788 SQ KM (196,058 SQ MI) OF THETOTAL AREA. MEASURED ALONG THE PARALLEL OF LATITUDE THAT PASSES THROUGH WEST QUODDY HEAD, MAINE, THEEASTERNMOST POINT IN THE UNITED STATES, THE MAXIMUM WIDTH OF THE CONTERMINOUS 48 STATES ISAPPROXIMATELY 4517 KM (ABOUT 2807 MI). THE MAXIMUM LENGTH MEASURED FROM THE VICINITY OF BROWNSVILLE, TEXAS,DUE NORTH TO THE CANADIAN FRONTIER IS ABOUT 2572 KM (ABOUT 1598 MI). THE BOUNDARIES OF THE UNITEDSTATES EXTEND ALONG THE ATLANTIC AND PACIFIC OCEANS, ALONG THE GULF OF MEXICO, AND ALONG LAND AREAS.THE NORTHERN BOUNDARY IS SOME 6420 KM (SOME 3990 MI) LONG; THE SOUTHERN BOUNDARY, SOME 3115 KM (SOME1935 MI); AND THE BOUNDARY BETWEEN ALASKA AND CANADA, SOME 2480 KM (SOME 1540 MI). FOR THE UNITEDSTATES, THE ATLANTIC COASTLINE IS 3330 KM (2069 MI) LONG; THE PACIFIC COASTLINE, EXCLUDING HAWAII,12,268 KM (7623 MI); THE GULF OF MEXICO COASTLINE, 2625 KM (1631 MI); AND THE ARCTIC COASTLINE OFALASKA, 1706 KM (1060 MI). MOUNT MCKINLEY, OR DENALI (6194 M/20,320 FT), IN ALASKA, IS THE HIGHEST POINTIN NORTH AMERICA; DEATH VALLEY, A DEPRESSION 86 M (282 FT) BELOW SEA LEVEL, IN CALIFORNIA, IS THELOWEST POINT. THE MEAN ELEVATION OF THE UNITED STATES IS ABOUT 760 M (ABOUT 2500 FT) ABOVE SEA LEVEL.LAND AND RESOURCES THE UNITED STATES HAS AN ENORMOUS VARIETY OF PHYSICAL FEATURES AND A WIDEDIVERSITY OF ANIMAL AND PLANT LIFE. BESIDES THE DISCUSSION BELOW, MUCH INFORMATION IS GIVEN IN THESEPARATE ARTICLES ON THE STATES, AS WELL AS THOSE ON IMPORTANT MOUNTAINS, RIVERS, LAKES, AND OTHERPHYSICAL FEATURES. GEOLOGIC HISTORY OF PHYSIOGRAPHIC REGIONS THE PRESENT-DAY PATTERN OF THELANDFORMS OF THE UNITED STATES IS THE RESULT OF A LONG SEQUENCE OF COLLISIONS AND SEPARATIONS OFLARGE BLOCKS OF THE EARTH'S SURFACE CRUST (SEE PLATE TECTONICS). THE OLDEST PART OF THE

CONTINENT ISTHE CANADIAN SHIELD, OR LAURENTIAN PLATEAU, A MASS OF GRANITE AND RELATED ROCK THAT UNDERLIESEASTERN CANADA AND THE NORTHEASTERN UNITED STATES. THE SHIELD WAS FORMED DURING SEVERAL LONG PERIODSOF CRUSTAL CONVERGENCE IN PRECAMBRIAN TIME (A PERIOD THAT STRETCHES FROM THE FORMATION OF THEEARTH TO ABOUT 570 MILLION YEARS AGO). DURING THESE SLOW BUT RELENTLESS COLLISIONS OF CRUSTAL PLATES,THE RIGID SURFACE ROCKS BUCKLED AND CRACKED. LARGE PIECES OF CRUST WERE FORCED DOWNWARD INTO THEHOT INTERIOR OF THE EARTH, WHERE THEY WARMED AND EVENTUALLY MELTED. THIS LIGHTER MOLTEN MATERIALTHEN MOVED UPWARD THROUGH THE CRUSTAL CRACKS, OCCASIONALLY ERUPTING AS A VOLCANO, BUT MORE OFTENPUSHING SURFACE ROCK UPWARD IN A BROAD BULGE, OR DOME. IN TIME, THE MOLTEN MATERIAL COOLED ANDCRYSTALLIZED. THE CHARACTERISTIC ROCK OF THE SHIELD IS GRANITE, A SLOWLY COOLED AND THEREFORECOARSE-GRAINED ROCK. THE MARGINS OF THE ANCIENT CONTINENT ARE MORE COMPLEX IN STRUCTURE, WITH ZONES OF GRANITE,DARKER OCEAN-BOTTOM ROCKS, FINE-GRAINED VOLCANIC ROCKS, HARDENED OCEAN SEDIMENTS, AND ROCKS OF ALLTYPES THAT WERE ALTERED BY HEAT AND PRESSURE DURING LATER CRUSTAL ACTIVITY. THE IRON DEPOSITS OFMINNESOTA, UPPER MICHIGAN, WISCONSIN, AND NORTHERN NEW YORK ALL OCCUR IN CONTORTED ROCKS NEARTHE EDGES OF THE ANCIENT SHIELD. A LONG PERIOD OF INACTIVITY IN THE CRUST FOLLOWED THE FORMATION OFTHE SHIELD. EROSION REDUCED THE MOUNTAINOUS CONTINENT TO A LOW PLAIN, AND THE ADJOINING SEAS WEREFILLED WITH THICK BEDS OF SEDIMENT. NEAR THE END OF THIS PERIOD, GREAT FORESTS COVERED THE LAND,AND THE ADDITION OF ORGANIC MATERIAL TO THE SEDIMENT FORMED THE VAST COAL AND PETROLEUM LAYERSTHAT STRETCH IN A BROAD CURVE FROM NORTHERN PENNSYLVANIA THROUGH WEST VIRGINIA TO ALABAMA, THENWEST TO TEXAS AND NORTHWEST THROUGH THE GREAT PLAINS STATES AND CANADIAN PRAIRIES TO ARCTIC ALASKA.GEOLOGICAL ACTIVITY AND CALM THE PERIOD OF

CRUSTAL CALM ENDED WHEN THE NORTH AMERICANAND EUROPEAN LANDMASSES COLLIDED EARLY IN THE FOSSIL-FORMING PERIOD; SOUTHERN MASSACHUSETTS ANDRHODE ISLAND ARE ACTUALLY PARTS OF THE EUROPEAN LANDMASS THAT BECAME ATTACHED TO THE AMERICAN PLATEAT THIS TIME. LATER, AFTER THE COAL-FORMING AGE, THE AFRICAN AND AMERICAN LANDMASSES CONVERGED.THE MODERN APPALACHIANS ARE THE WORN-DOWN REMNANTS OF LOFTY MOUNTAINS THAT WERE BUILT DURING THISMAJESTIC COLLISION. THIS WAS AN AGE OF EARTHQUAKES AND VOLCANOES, THE SAME KIND OF INTERMITTENT BUTRELENTLESS GEOLOGIC ACTIVITY THAT CHARACTERIZES CALIFORNIA, WASHINGTON, AND ALASKA TODAY. CRUSTALUPLIFT AND SUBSEQUENT EROSION EXPOSED ANCIENT GRANITE ROCKS ALL THE WAY FROM NEW ENGLAND TO ALABAMA, ASEVIDENCED IN THE LOW PIEDMONT HILLS OF GEORGIA AND THE CAROLINAS AND THE SOMEWHAT HIGHER BLUE RIDGEMOUNTAINS OF NORTH CAROLINA, VIRGINIA, AND WEST VIRGINIA. TO THE WEST, THE LAYERS OF YOUNGERSEDIMENTARY ROCKS STILL REMAIN AT THE SURFACE, CRUMPLED AND ERODED, NOTABLY INTHE LONG, EVEN RIDGES ANDVALLEYS OF CENTRAL PENNSYLVANIA, EASTERN TENNESSEE, AND THE OUACHITA REGION OF ARKANSAS AND OKLAHOMA.STILL FARTHER WEST AND NORTH, LESS INTENSE FOLDING CREATED BROAD DOMES AND BASINS. PRESENT-DAYMICHIGAN AND IOWA OCCUPY GEOLOGIC BASINS. STRUCTURAL DOMES ARE CENTERED NEAR THE WISCONSIN DELLS, THEBLUEGRASS AREA OF KENTUCKY, AND THE NASHVILLE AREA OF TENNESSEE. AFTER THE APPALACHIAN COLLISION,THE CONTINENT REVERSED DIRECTION AND DRIFTED WEST. THE ATLANTIC OCEAN BEGAN TO WIDEN, AND THEEASTERN UNITED STATES AGAIN BECAME A REGION OF GEOLOGIC CALM. THE LOFTY APPALACHIANS BEGAN TO ERODE,AND THE RESULTING SEDIMENT ACCUMULATED ON THE MIDCONTINENTAL GREAT PLAINS AND ON THE ATLANTICAND GULF COASTAL PLAINS. MEANWHILE, NEW RANGES OF MOUNTAINS WERE RISING AS THE WESTERN UNITEDSTATES COLLIDED WITH THE PACIFIC PLATE. LAVA ERUPTED ONTO THE SURFACE IN MANY PLACES AT DIFFERENT

TIMES: IN NORTHERN NEW MEXICO, CENTRAL ARIZONA, EASTERN CALIFORNIA, AND SOUTHERN IDAHO, ANDESPECIALLY IN THE REGION OF THE CASCADE RANGE OF OREGON AND WASHINGTON. THE SANDY SEDIMENTS OF THE GREATPLAINS WERE THRUST SHARPLY UPWARD ALONG THE FRONT RANGE OF THE ROCKY MOUNTAINS IN COLORADO ANDMONTANA AND AROUND SMALLER MOUNTAIN RANGES SUCH AS THE BLACK HILLS OF SOUTH DAKOTA. ROCK MOVEMENTALONG MASSIVE FAULTS FORMED CALIFORNIA'S SIERRA NEVADA, UTAH'S WASATCH RANGE, NEVADA'S ALIGNEDMOUNTAIN RANGES, AND THE TETON RANGE IN WYOMING. THE LAND OF ARIZONA AND SOUTHERN UTAH WAS LIFTED, ANDRIVERS CUT CANYONS IN THE LEVEL SEDIMENTARY ROCKS. EFFECTS OF CLIMATE THE MOTION OF CRUSTALPLATES THUS ACCOUNTS FOR THE BROAD PANORAMA OF THE LANDFORMS OF THE UNITED STATES. INTERPRETINGTHE FINER DETAILS OF THE PRESENT-DAY LANDSCAPE REQUIRES CONSIDERATION OF THE EFFECTS OF PAST ANDPRESENT CLIMATES. THE MAJOR PAST CLIMATIC EVENT IS THE PLEISTOCENE EPOCH, MORE COMMONLY KNOWN AS THEICE AGE (SEE ICE AGES). AT LEAST FOUR TIMES IN THE PAST 1 MILLION YEARS, GREAT ICE SHEETS FORMEDIN EASTERN CANADA AND THE MOUNTAINS OF THE WEST AND SPREAD OUTWARD. THE MOVING ICE, LIKE A POWERFULBULLDOZER, SCRAPED SOIL AND ROCK FROM CANADA AND THE NORTHERN UNITED STATES AND DEPOSITED MATERIALFARTHER SOUTH. THE ALIGNED LAKES AND EXPOSED ROCKS OF NEW ENGLAND AND NORTHERN MINNESOTA ARERESULTS OF GLACIAL SCOURING. LONG ISLAND AND CAPE COD ARE HUGE GLACIAL DEPOSITS, CHARACTERIZED BYHILLS COMPOSED OF ROCK AND SOIL, WITH ASSOCIATED SWAMPS AND SAND OUTWASH PLAINS; SIMILAR FEATURESARE ABUNDANT THROUGHOUT THE FORMER GLACIATED AREAS, FROM NEW ENGLAND TO THE DAKOTAS AND IN THEWESTERN MOUNTAIN VALLEYS. RIVERS SUCH AS THE HUDSON, ILLINOIS, MINNESOTA, MISSOURI, AND COLUMBIACARRIED HUGE FLOODS OF GLACIAL MELTWATER AND CARVED VALLEYS MUCH LARGER THAN THE PRESENT-DAY STREAMSREQUIRE. GLACIAL MELTWATER ALSO FORMED MANY LARGE LAKES. TODAY LEVEL PLAINS MARK THE BEDS AND LOWBEACH RIDGES MARK THE SHORES OF ICE AGE LAKES ON BOTH THE EASTERN AND WESTERN EDGES OF VERMONT,AROUND THE MAUMEE RIVER OF NORTHWESTERN OHIO, IN THE SAND COUNTIES OF CENTRAL WISCONSIN, AROUNDTHE RED RIVER OF MINNESOTA AND THE DAKOTAS,

AROUND THE GREAT SALT LAKE OF UTAH, AND IN THEMISSOULA BASIN OF MONTANA, THE CENTRAL VALLEY OF CALIFORNIA, AND HUNDREDS OF SMALLER AREAS IN MANYSTATES. ICE AGE DUST STORMS LEFT THICK DEPOSITS OF LOESS (FINE-GRAINED SILT OR CLAY) ON THEUNDULATING PLAINS AROUND THE MISSISSIPPI RIVER AND MISSOURI RIVER, ON THE STEEPER BLUFFS OF WESTERNWISCONSIN AND WESTERN TENNESSEE, AND IN THE PALOUSE HILLS REGION OF EASTERN WASHINGTON. TIMES OFHIGHER SEA LEVEL BUILT BEACHES FAR UP ON THE GULF COASTAL PLAIN AND ON SLOPES OVERLOOKING THE PACIFICOCEAN; ON THE OTHER HAND, CHESAPEAKE BAY AND MANY SIMILAR DROWNED RIVER VALLEYS ALONG THEATLANTIC COAST FROM GEORGIA TO CONNECTICUT ARE RESULTS OF PERIODS OF LOWER SEA LEVEL. CLIMATETHE CLIMATE OF A PLACE IS THE SEASONAL PATTERN OF ITS INPUTS OF SOLAR ENERGY, WIND, ANDPRECIPITATION. WITH THE EXCEPTION OF THE PRINCIPAL ISLANDS OF HAWAII, NO PLACE IN THE UNITED STATES EVER SEESTHE SUN DIRECTLY OVERHEAD. IN GENERAL, SUN INTENSITY AND, CONSEQUENTLY, TEMPERATURES DECREASE FROMSOUTH TO NORTH; IN SUMMER, HOWEVER, THE DECREASE IN INTENSITY IS PARTLY OFFSET BY LONGER DAYS INTHE NORTH. MONTANA, NORTH DAKOTA, AND MINNESOTA ACTUALLY HAVE HIGHER RECORD TEMPERATURES THAN NEWMEXICO AND ALABAMA. IN WINTER, ON THE OTHER HAND, THE SHORT DAYS IN THE NORTH EXAGGERATE THEEFFECT OF LOW SUN ANGLES, CREATING WIDE TEMPERATURE DIFFERENCES FROM SOUTH TO NORTH. FORESTS USE MUCHSOLAR ENERGY TO EVAPORATE WATER, AND THEREFORE THE HUMID STATES OF THE EASTERN UNITED STATES DONOT GET AS WARM AS THE DRY WESTERN DESERTS. OCEANS AND LAKES MODERATE TEMPERATURES; THIS IS ESPECIALLYTRUE OF THE WESTERN COAST, WHERE THE OCEAN IS COOL AND THE WIND IS USUALLY ONSHORE. FINALLY,MOUNTAINS ARE SOMEWHAT COOLER BY DAY AND MUCH COLDER AT NIGHT THAN SURROUNDING LOWLANDS. EFFECTS OF EACHOF THESE FACTORS CAN BE SEEN IN THE ACCOMPANYING TABLE OF TEMPERATURES. THE PATTERN OFPRECIPITATION IS LARGELY A CONSEQUENCE OF THE INTERACTION OF WIND AND TOPOGRAPHY. THE WIND SYSTEM OF THEEARTH BEHAVES WITH ONE SIMPLE GOAL: TO EQUALIZE

TEMPERATURES ON EARTH BY TAKING HEAT FROM THEEQUATOR AND CARRYING IT TO THE POLES. THE PROCESS IS GRAND IN SCOPE AND COMPLEX IN DETAIL. TWOFEATURES OF GLOBAL ATMOSPHERIC CIRCULATION ARE PARTICULARLY SIGNIFICANT FOR THE UNITED STATES. ONE IS ACURRENT OF SINKING AIR, A GENTLE, BUT PERSISTENT, DOWNWARD MOVEMENT OF AIR FROM THE UPPER ATMOSPHERE.THIS SUBSIDENCE IS PART OF THE GLOBAL CONVECTION CYCLE AND STARTS WITH UPDRAFTS OF WARM AND HUMIDAIR NEAR THE EQUATOR; THE AIR LOSES MOISTURE AS IT RISES TO THE UPPER ATMOSPHERE AND BEGINS TO MOVEPOLEWARD. AT ABOUT LATITUDE 30 NORTH THE AIR BEGINS TO SINK, BRINGING HOT AND DRY CONDITIONS TOTHE SOUTHWESTERN UNITED STATES, ESPECIALLY IN SUMMER. THE OTHER SIGNIFICANT PART OF ATMOSPHERICCIRCULATION IS THE JET STREAM, A SHIFTING ZONE OF FAST WINDS BLOWING GENERALLY FROM WEST TO EASTHIGH ABOVE THE GROUND. THE PATH OF THE JET STREAM ON ANY GIVEN DAY IS A KEY TO SURFACE WEATHER. INSUMMER, THE JET STREAM IS USUALLY NEAR THE CANADIAN BORDER, ALTHOUGH ON ANY GIVEN DAY IT MAY LOOPAS FAR NORTH AS ALASKA OR AS FAR SOUTH AS LOUISIANA. THE JET BRINGS WET PACIFIC AIR ONSHORE INWASHINGTON AND ALASKA, BUT IN OTHER WESTERN STATES DRY AIR MASSES FROM MEXICO AND CANADA DOMINATE. INTHE EAST, BY CONTRAST, THE JET CAN PULL MOIST AIR MASSES NORTHWARD FROM THE GULF OF MEXICO ALLTHE WAY TO CANADA. IN WINTER, THE ENTIRE WIND SYSTEM FOLLOWS THE SUN SOUTHWARD. PACIFIC AIR MASSESNOW BRING CLOUDS AND RAIN TO THE COASTAL MOUNTAINS FROM CALIFORNIA TO SOUTHERN ALASKA. THE JETUSUALLY CROSSES THE COUNTRY AT THE LATITUDE OF OKLAHOMA, AND COLD, DRY CANADIAN AIR COVERS THENORTHERN HALF OF THE COUNTRY; HOWEVER, DAY-TO- DAY SHIFTS OF THE JET MAY PULL WARM, MOIST GULF AIR AS FARNORTH AS ILLINOIS OR BRING CANADIAN AIR TO FLORIDA. REGIONAL WEATHER HAZARDS ARE INTIMATELYASSOCIATED WITH THE SEASONAL POSITION OF THE JET STREAM AND ASSOCIATED FRONTS. TORRENTIAL RAINS ARE MOSTCOMMON IN THE UNITED STATES NEAR THE GULF OF

MEXICO, WHICH IS THE MAJOR SOURCE OF MOISTURE FOR THECOUNTRY. TORNADOES OCCUR IN THE CENTER OF THE UNITED STATES, WHERE CANADIAN AND GULF AIR MASSESOFTEN COLLIDE VIOLENTLY. SOUTHERN CALIFORNIA HAS SMOG EPISODES AND FOREST FIRES IN LATE SUMMER, WHENTHE JET STREAM AND ITS ASSOCIATED RAIN ARE FAR TO THE NORTH AND THE HOT, DRY SINKING AIR FROMTHE TROPICAL CIRCULATION DOMINATES THE WEATHER. HURRICANES ARISE OUT OF THE LATE-SUMMER WARMTH OF THEATLANTIC OCEAN AND DRIFT TOWARD THE SOUTHEASTERN STATES IN THE AUTUMN. HEAVY WINTER SNOWS IN THEEASTERN UNITED STATES ARE CAUSED BY THE RAPID COOLING OF THE GULF AIR, AMPLIFIED IN THE GREAT LAKESREGION BY LOCAL LAKE BREEZES. DECEMBER AND MARCH ARE THE MAJOR SNOW MONTHS IN MINNESOTA AND THEDAKOTAS; JANUARY THERE IS A TIME OF INTENSE COLD AND LITTLE SNOWFALL, BECAUSE GULF AIR CANNOTPENETRATE THIS FAR NORTH IN MIDWINTER. FINALLY, THE OCCASIONAL KONA (WEST COAST) STORMS OF HAWAII AREWINTERTIME INCURSIONS OF NORTH PACIFIC AIR THAT OCCUR WHEN THE JET STREAM CURVES FAR TO THE SOUTH.NORMAL WEATHER CONSISTS OF TRADE WINDS THAT CAUSE RAIN ONLY ON THE NORTHEASTERN SLOPES OF EACH ISLAND.RIVERS AND LAKES RIVERS RESPOND TO THE QUANTITY AND SEASONAL PATTERN OF PRECIPITATION INA REGION. THE STREAMS OF THE EASTERN UNITED STATES, PRINCIPAL AMONG WHICH ARE THE HUDSON, DELAWARE,SUSQUEHANNA, POTOMAC, AND SAVANNAH, RECEIVE RAINFALL IN EVERY MONTH AND THEREFORE ARE RELIABLEAVENUES FOR WATERBORNE COMMERCE. RIVERS OF THE INTERIOR, SUCH AS THE OHIO, TENNESSEE, ILLINOIS, ANDMISSISSIPPI, OFTEN FLOOD IN SPRING AND DECREASE IN SIZE DURING THE HOT WEEKS OF LATE SUMMER AND THE SNOWMONTHS OF WINTER. SOME FLOW REGULATION AND FLOOD CONTROL HAVE BEEN ACHIEVED ON THESE RIVERS THROUGHA COSTLY AND CONTROVERSIAL SYSTEM OF DAMS AND LEVEES. ARGUMENT OVER WATER PROJECTS IS EVEN MOREHEATED IN THE WESTERN UNITED STATES, WHERE MOUNTAIN SNOWMELT IS THE PRINCIPAL SOURCE OF

WATER FOR THEEASTWARD-FLOWING MISSOURI, PLATTE, ARKANSAS, AND RIO GRANDE RIVERS AND THE WESTWARD-FLOWING COLORADO,SACRAMENTO, SNAKE, AND COLUMBIA RIVERS. MOST OF THESE RIVERS SHRINK IN VOLUME AS THEY FLOW AWAYFROM THEIR MOUNTAIN SOURCES; SOME, LIKE THE COLORADO, ARE DAMMED AND DIVERTED FOR SO MANY URBAN ORAGRICULTURAL USES THAT THEY NO LONGER CARRY WATER TO THE SEA. ALONG THE PACIFIC SEABOARD ARE A FEWCOASTAL STREAMS THAT HAVE THEIR SEASONAL PEAKS DURING THE WINTER RAINY SEASON. IN ALASKA THE DRAINAGESYSTEM IS DOMINATED BY THE YUKON, A RIVER AS LONG AS THE RIO GRANDE BUT CONSIDERABLY GREATER IN VOLUME.THE SURFACE WATER SOURCES OF THE NATION ALSO INCLUDE THE FIVE GREAT LAKES, WHICH OCCUPY ANINTERCONNECTED SET OF GLACIALLY SCOURED BASINS AND TOGETHER SERVE AS A MAJOR TRANSPORTATION ARTERY. GLACIERSALSO LEFT TENS OF THOUSANDS OF SMALLER LAKES THROUGHOUT THE NORTHEASTERN UNITED STATES, THE UPPERMIDWEST, AND MUCH OF ALASKA. AMONG THE LARGER OF THESE ARE CHAMPLAIN, WINNIPESAUKEE, AND CAYUGA INTHE NORTHEAST AND WINNEBAGO, RED, AND MILLE LACS IN THE MIDWEST. THE GREAT SALT LAKE OF UTAH AND MANYSMALLER SALT BASINS OF THE MOUNTAIN STATES ARE REMNANTS OF MUCH LARGER ICE AGE LAKES. MANYGROUNDWATER AQUIFERS, ESPECIALLY THOSE OF THE GREAT PLAINS, ARE ALSO RELICS OF WETTER CLIMATES OF THE PAST.SOILS SOILS, LIKE LANDFORMS, ARE FORMED BY THE ACTION OF CLIMATE ON SURFACE MATERIAL. THECENTRAL INTERIOR PLAINS ARE JUST FAR ENOUGH SOUTH TO HAVE ADEQUATE HEAT FOR ROCK DECOMPOSITION ANDPLANT PRODUCTION DURING THE GROWING SEASON. THE MOISTURE BALANCE HERE IS ALSO GENERALLY FAVORABLE:ENOUGH RAINFALL FOR CROPS BUT NOT SO MUCH THAT VITAL NUTRIENTS WILL BE LEACHED FROM THE SOIL. FARTHERSOUTH, EXCESS HEAT ACCELERATES THE CHEMICAL WEATHERING AND STIMULATES THE GROWTH OF MICROORGANISMS,WHICH CONSUME ORGANIC RESIDUES AND LEAVE A LESS FERTILE RED OR YELLOW MINERAL SOIL. IN THE HUMID EAST

AND NORTHEAST, SURPLUS WATER SEEPS DOWN THROUGH THE SOIL AND REMOVES VALUABLE NUTRIENT SALTS. AT THEOTHER EXTREME, SOILS IN THE DRY CLIMATES OF THE WEST AND SOUTHWEST CAN ACCUMULATE SALTS, OFTEN TOLEVELS THAT ARE TOXIC TO PLANTS. DURING THE ICE AGE, GLACIERS SCOURED MATERIAL FROM THE ALREADY THINAND POOR SOILS OF THE NORTH AND MOVED A SUBSTANTIAL AMOUNT OF EARTH SOUTHWARD. ILLINOIS, INDIANA,IOWA, AND OHIO WERE THE PRINCIPAL BENEFICIARIES; MANY PARTS OF THESE STATES HAD MORE THAN 30 M (100FT) OF NEW EARTH LAID DOWN AS GENTLY UNDULATING TILL PLAIN. PARTS OF NEW ENGLAND, NEW YORK, MICHIGAN,WISCONSIN, AND MINNESOTA ALSO GAINED MATERIAL, BUT OFTEN OF A MORE COARSE AND ROCKY NATURE.MELTWATER FLOODS FILLED MANY VALLEYS IN THE MIDWEST AND WEST WITH RICH SEDIMENT, AND UPLAND SOILS WEREOFTEN ENRICHED BY FINE WINDBLOWN DUST. THE UNITED STATES CAN THUS BE DIVIDED INTO FIVE MAJOR SOILREGIONS THAT ARE A RESULT OF THESE CONTINUING FORMATIVE FORCES: (1) THE DEEP, BLACK MOLLISOLS OF THEMIDCONTINENT (THE COUNTRY'S MOST FERTILE), IN AN AREA STRETCHING FROM ILLINOIS WEST TO NEBRASKA AND THEDAKOTAS; (2) THE LEACHED RED ULTISOLS OF THE SOUTHEASTERN AND WESTERN COAST MOUNTAINS, WHICH ARECONSIDERABLY LESS FERTILE; (3) THE COARSE AND ACID SPODOSOLS IN THE NORTHEASTERN UNITED STATES AND INTHE HIGH WESTERN MOUNTAINS; (4) THE MODERATELY FERTILE GRAY OR BROWN ALFISOLS FOUND AROUND THE GREATLAKES, ON THE SOUTHERN GREAT PLAINS, AND IN THE CENTRAL VALLEY OF CALIFORNIA; AND (5) THE DRY,SALTY ARIDSOLS OF THE DESERT SOUTHWEST. SUPERIMPOSED ON THESE BROAD PATTERNS ARE LOCAL GEOLOGICEXCEPTIONS, SUCH AS THE BLACK CLAY VERTISOLS OF TEXAS AND THE ORGANIC HISTOSOLS, WHICH ARE PEAT AND MUCKSOILS FOUND IN SWAMPY PLACES SUCH AS THE FLORIDA EVERGLADES OR THE MINNESOTA BOGS. YOUNGER SOILS, SUCHAS ENTISOLS AND INCEPTISOLS, OCCUR ON SHIFTING

SAND DUNES, RECENT VOLCANOES, RIVER FLOODPLAINS, ANDSTEEP SLOPES, WHERE DISTURBANCES SUCH AS FLOODS OR LANDSLIDES PREVENT THE DEVELOPMENT OF MATURESOIL PROFILES. THESE IMMATURE SOILS RANGE FROM BARREN ROCK OUTCROPS IN ARIZONA AND GRASSY SANDHILLS INNEBRASKA TO FERTILE VOLCANIC ASH SOILS IN HAWAII AND THE EXTRAORDINARILY PRODUCTIVE FLOODPLAIN OFTHE MISSISSIPPI RIVER. VEGETATION BECAUSE PLANTS RESPOND DIRECTLY TO LOCAL CLIMATE AND TO ALESSER DEGREE TO LOCAL TOPOGRAPHY, THE INDIGENOUS VEGETATION OF THE UNITED STATES IS MARKED BY GREATDIVERSITY. IN REGIONS OTHER THAN THOSE DOMINATED BY FORESTS ARE A WIDE VARIETY OF PLANTS THAT AREADAPTED TO COLDER OR DRIER CONDITIONS. AT THE TIME EUROPEAN SETTLEMENT BEGAN, ABOUT ONE-HALF OF THEUNITED STATES WAS COVERED BY FORESTS. TODAY, BECAUSE OF EXTENSIVE HUMAN MODIFICATION, ABOUT 30PERCENT OF THE COUNTRY'S LAND AREA IS FORESTED. SIMILARLY, GRASSLANDS AND OTHER NATURAL VEGETATIVE COVERDECREASED IN EXTENT AS THE CONTINENT WAS SETTLED. NORTHERN ALASKA, LOCATED IN THE NORTHERNMOSTPART OF THE UNITED STATES, IS CHARACTERIZED BY A WINDSWEPT TUNDRA, A REGION OF LICHENS, MOSSES, HARDYLOW SHRUBS, AND FLOWERING PLANTS. INLAND AND TO THE SOUTH, THE GROWING SEASON LENGTHENS ANDCERTAIN TREES CAN SURVIVE. A FEW SPECIES OF NEEDLE-LEAF TREES, NOTABLY SPRUCES AND FIRS, DOMINATE AVAST BUT SLOW-GROWING EVERGREEN FOREST, INTERSPERSED WITH LICHEN-COVERED ROCKY AREAS, GRASSY SWAMPS,AND ASPEN-CHOKED FIRE SCARS. THIS FOREST, KNOWN AS THE TAIGA, STRETCHES SOUTHEAST FROM INTERIORALASKA AND HAS SMALL OUTLIERS IN NORTHERN NEW ENGLAND AND THE GREAT LAKES REGION. SOUTH OF THE TAIGATHE GROWING SEASON IS STILL LONGER AND MORE TREE SPECIES CAN SURVIVE. HERE IS FOUND A MIXEDFOREST CONTAINING BOTH NEEDLE-LEAF AND BROADLEAF TREES, AND INCLUDING PINES, MAPLES, ELMS, BIRCHES,AND OAKS, AS WELL AS HICKORY, BEECH, AND SYCAMORE. THIS TYPE OF MIXED FOREST COVERED THE REGIONAROUND THE GREAT LAKES AND MOST OF THE NEW

ENGLAND AND MIDDLE ATLANTIC STATES WHEN EUROPEAN SETTLERSARRIVED. STILL FARTHER SOUTH, THE FROST-FREE SEASON EXCEEDS SIX MONTHS, RAINFALL BECOMES MORERELIABLE, AND THE FOREST REACHES ITS MAXIMUM DIVERSITY. THE GREAT SMOKY MOUNTAINS NATIONAL PARK INWESTERN NORTH CAROLINA AND EASTERN TENNESSEE CONTAINS MORE TREE SPECIES THAN THE ENTIRE CONTINENT OFEUROPE. THE GULF OF MEXICO COAST IS EVEN WARMER THAN THIS MOUNTAINOUS AREA, BUT ITS PLAINS AND LOWHILLS DO NOT SUPPORT AS COMPLEX A FOREST. MOREOVER, THE SANDY SOILS AND HOT SUMMERS ENCOURAGEFIRES, WHICH SUPPRESS OAKS AND OTHER HARDWOODS AND FAVOR THE FAST-GROWING PINES THAT NOW REPRESENTTHE MAJOR FOREST RESOURCE OF THE NATION. OTHER SPECIES FOUND HERE INCLUDE SOUTHERN MAGNOLIA,PECAN, RED GUM, AND BLACK GUM (TUPELO). A NUMBER OF SUBTROPICAL AND TROPICAL TREES FLOURISH IN SOUTHERNFLORIDA. ALONG THE COAST OF THE GULF OF MEXICO, SALT MARSHES AND GROVES OF CYPRESS AND MANGROVEHELP TO ARMOR THE SHORE AGAINST THE ERODING FORCES OF WIND AND WATER. THE DIVERSITY OF THE FORESTALSO DECREASES WEST OF THE APPALACHIAN MOUNTAINS. FIRST, THE MOUNTAINTOP SPRUCES, FIRS, ANDMOUNTAIN ASHES DISAPPEAR. THEN, RAINFALL DECREASES IN QUANTITY AND RELIABILITY, AND FIRES BECOME MOREFREQUENT. THE LUSH BOTTOMLAND HARDWOOD FORESTS OF THE MISSISSIPPI VALLEY SLOWLY DWINDLE IN SIZE ANDCOMPLEXITY. OAK-HICKORY FORESTS GIVE WAY TO ISOLATED STANDS OF OAK AND THEN TO TALL GRASSPRAIRIES, WHICH, BEFORE CULTIVATION, OCCUPIED THE PRESENT CORN BELT FROM INDIANA TO THE EASTERN GREATPLAINS. FARTHER WEST, THE CLIMATE BECOMES STILL DRIER, AND THE TALL BLUESTEM GRASSES YIELD TOSHORTER GRAMA AND WHEATGRASS RANGES. THE GRASSES OF THE NORTHERN GREAT PLAINS GROW ONLY DURING THESHORT SUMMER AND FLOWER IN LATE SUMMER OR EARLY AUTUMN. BY CONTRAST, THE GRASSES OF THE SOUTHERNGREAT PLAINS GROW RAPIDLY IN SPRING, FLOWER EARLY, AND THEN GO DORMANT DURING THE HOT, DRYSUMMERS. BOTH KINDS OF GRASS BECOME LESS PRODUCTIVE AS RAINFALL CONTINUES TO DIMINISH

TOWARD THE WEST.SHRUBBY SAGEBRUSH (IN THE NORTH) AND MESQUITE AND JUNIPER (IN TEXAS) ARE TYPICAL INVADERS ON POORERGRASSLANDS THAT HAVE BEEN OVERGRAZED OR PROTECTED FROM FIRES. A GRADUAL TRANSITION TO TRUE DESERTVEGETATION IS INTERRUPTED BY THE ROCKY MOUNTAINS AND OTHER RANGES, THE ELEVATION OF WHICH BOTHINCREASES RAINFALL AND DECREASES TEMPERATURE AND EVAPORATION. TREES BECOME PROMINENT ON THE LOWER ANDMIDDLE SLOPES. HARDY PINES AND JUNIPERS DOMINATE AT LOWER ELEVATIONS, GIVING WAY TO ASPENS, FIRS, ANDSPRUCES AT HIGHER ELEVATIONS. STILL HIGHER, THE SPRUCES AND FIRS BECOME STUNTED AND WIDELYSPACED. ABOVE THIS ZONE IS TREELESS TUNDRA, OUTWARDLY SIMILAR TO ARCTIC VEGETATION, ALTHOUGH THE TWOKINDS OF TUNDRA HAVE DIFFERENT PATTERNS OF SOLAR RADIATION, DAY LENGTH, AND DIURNAL (DAY-TO-NIGHT)TEMPERATURE CHANGES. SHRUBBY LOW- LYING DESERTS ALTERNATE WITH FORESTED (AND OCCASIONALLY TUNDRA-OR ICE- CAPPED) MOUNTAINS ACROSS ALL OF THE MOUNTAIN STATES AND INTO THE PACIFIC STATES. THISREGION IS AGRICULTURALLY PRODUCTIVE ONLY WHEN MASSIVE INVESTMENTS ARE MADE IN IRRIGATION. DEATHVALLEY, WHICH LIES BELOW SEA LEVEL, IS BUT ONE OF THE MANY NEARLY BARREN LOWLANDS. VEGETATION IN THESEREGIONS INCLUDES SPECIES SUCH AS SAGEBRUSH, JUNIPER,PIDON, RABBITBRUSH, MESQUITE, CREOSOTE BUSH, AND YUCCA; THE CACTUS FORESTS THAT FORM A POPULAR IMAGEOF DESERTS ARE ACTUALLY FOUND ON THE SLOPES OF MOUNTAIN RANGES IN THE MOJAVE DESERT OF SOUTHERNARIZONA AND CALIFORNIA. ON THE HIGHER BUT STILL RELATIVELY DRY COLORADO PLATEAU ARE FOUND PONDEROSAAND PIDON PINES. THE HOT, DRY SUMMERS AND MILD, MOIST WINTERS OF COASTAL SOUTHERN CALIFORNIAPRODUCE A DISTINCTIVE SHRUB VEGETATION KNOWN AS CHAPARRAL. THE PLANTS HERE HAVE ADAPTED TO RAINYWINTERS, DRY SUMMERS, AUTUMN FIRES, AND THIN SOILS. FARTHER NORTH ON THE WESTERN SLOPES OF THE COASTALHILLS AND SIERRA NEVADA, THE WINTER RAINY SEASON IS LONGER; FORESTS OF GIANT SEQUOIA AND REDWOODOCCUPY THIS FAVORED LOCATION, WHERE THERE IS ENOUGH RAIN TO PERMIT RAPID GROWTH BUT A LONG ENOUGH

DRY SEASON TO DISCOURAGE COMPETITION FROM NUMEROUS SPECIES. STILL FARTHER NORTH, IN WESTERN OREGON ANDWASHINGTON, A TRUE RAIN FOREST APPEARS AS THE DRY PERIODS SHRINK TO LESS THAN A FEW WEEKS INMIDSUMMER. THIS LUXURIANT FOREST CONSISTS PRIMARILY OF A GREAT VARIETY OF NEEDLE-LEAF TREES: DOUGLASFIRS, TRUE FIRS, HEMLOCKS, CEDARS, SPRUCES, AND PINES, EACH OCCUPYING ITS OWN PREFERRED ELEVATIONZONE HERE, AND TOGETHER CONSTITUTING THE SECOND RICHEST FOREST RESOURCE FOR THE NATION. THE COASTALFORESTS OF ALASKA HAVE FEWER SPECIES THAN THE RICH RAIN FOREST TO THE SOUTH BUT A FASTER GROWTHTHAN THE TAIGA TO THE NORTH. THE NATURAL VEGETATION OF HAWAII IS CONDITIONED BY ITS ISOLATION,WHICH HAS SERVED TO LIMIT THE NUMBER OF SPECIES, AND BY THE INTERPLAY OF ITS MOUNTAINS AND THE MOISTTRADE WINDS. FORESTS DOMINATED BY GUAVA TREES ON THE WINDWARD (NORTHEAST) COASTS OF THE ISLANDSGRADE UPWARD TO A RICH BUT SWAMPY RAIN FOREST AT MODERATE ELEVATIONS, WHERE THE ANNUAL RAINFALLMAY EXCEED ABOUT 10,000 MM (ABOUT 400 IN). THE HIGH MOUNTAINS SUPPORT SHRUB FOREST, AND PATCHESOF TUNDRA ARE FOUND ON THE SUMMITS OF THE HIGHEST PEAKS, MAUNA LOA AND MAUNA KEA. THE DRY LEEWARD(SOUTHWEST) COASTS ARE V IRTUAL DESERTS, WITH SPINY KOA AND KIAWE SHRUBS GROWING ON THE SLIGHTLYWETTER SLOPES. ANIMALS ANIMALS DEPEND, EITHER DIRECTLY OR INDIRECTLY, ON PLANTS FORTHEIR SURVIVAL. EACH MAJOR VEGETATION REGION THUS HAS ITS OWN CHARACTERISTIC KINDS OF ANIMAL LIFE. INTHE ARCTIC AREAS AND REGIONS OF MOUNTAIN TUNDRA ARE FOUND BURROWING MARMOTS, GROUND SQUIRRELS,COLD-WATER FISH SUCH AS GRAYLING AND TROUT, AND AN OCCASIONAL BEAR. ALASKAN COASTAL WATERS ARE THEHABITAT OF A NUMBER OF LARGE MAMMALS, INCLUDING WALRUS AND FUR SEALS. CARIBOU AND ELK SPEND SUMMERS ON THETUNDRA BUT MIGRATE INTO THE CONIFER FOREST FOR WINTER. MANY BIRDS MIGRATE EVEN FARTHER, GOING FROMTHE POLAR REGIONS TO THE TROPICS EACH WINTER. THE HARDWOOD FORESTS OF THE EASTERN UNITED STATESCONTAIN MOOSE, BLACK BEARS, DEER, FOXES,

RACCOONS, SKUNKS, SQUIRRELS, AND A DIVERSITY OF SMALL BIRDS.ALONG THE GULF OF MEXICO COAST LIVE LARGER AND MORE COLORFUL BIRDS SUCH AS PELICANS, FLAMINGOS, ANDGREEN KINGFISHERS, AS WELL AS ALLIGATORS AND WARMWATER FISH SUCH AS CATFISH. SEVERAL VARIETIES OFVENOMOUS SNAKES ARE ALSO FOUND HERE. BISON (BUFFALO) ARE POPULARLY ASSOCIATED WITH THE GRASSLANDS,ALTHOUGH IN FACT THEY ONCE RANGED OVER MOST OF EASTERN NORTH AMERICA BEFORE BEING NEARLY EXTERMINATED BYHUNTING; THEY NOW EXIST ONLY IN CAPTIVITY OR IN PROTECTED AREAS. GOPHERS, RABBITS, PRAIRIE DOGS,FERRETS, ANTS, AND OTHER BURROWING CREATURES ARE BEST SUITED TO THE GRASSLANDS, WHICH WERE ONCE SWEPTBY FIRES. THE MOUNTAINOUS WESTERN STATES, ESPECIALLY ALASKA, ARE THE LAST REFUGES IN THE UNITEDSTATES OF MOST BIG-GAME ANIMALS. HERE MAY BE FOUND ELK, PRONGHORN, MOOSE, DEER, BIGHORN SHEEP, MOUNTAINGOATS, TIMBER WOLVES, AND, IN A FEW REMOTE AREAS, BROWN BEARS. THE KODIAK BEAR, THE LARGEST CARNIVOREIN NORTH AMERICA, IS FOUND IN ALASKA. THE DESERTS HAVE FEW PLANTS, FEWER SMALL ANIMALS, AND ALMOSTNO LARGE ANIMALS. KANGAROO RATS, LIZARDS, AND WIDE-RANGING BIRDS ARE TYPICAL ANIMALS IN THIS HARSHREGION. THE ANIMALS OF HAWAII INCLUDE MANY ENDEMIC SPECIES (THOSE NOT FOUND ELSEWHERE), BUT MANY OFTHESE HAVE BEEN DRIVEN TO NEAR EXTINCTION BY HUMAN ALTERATION OF THE HABITAT AND BY COMPETITION FROMINTRODUCED ANIMALS. HAWAII'S ONLY INDIGENOUS MAMMAL IS THE BAT. RESOURCES AND ENVIRONMENTALPROTECTION THE UNITED STATES IS EXCEEDINGLY RICH IN NATURAL RESOURCES. THE COUNTRY'S CLIMATE ISFAVORABLE FOR A DIVERSITY OF CROPS AND FOREST PRODUCTS. THE CORN BELT, A REGION STRETCHING FROMWESTERN OHIO TO CENTRAL NEBRASKA, IS THE LARGEST EXPANSE OF PRIME FARMLAND IN THE WORLD. SIGNIFICANTDEPOSITS OF MANY IMPORTANT MINERALS, INCLUDING MORE THAN A FIFTH OF THE WORLD'S COAL, ARE PRESENT WITHIN

THE COUNTRY'S BORDERS. DESPITE THIS WEALTH, THE UNITED STATES CANNOT PRODUCE ALL THE RESOURCESNEEDED BY ITS LARGE INDUSTRIAL ECONOMY. THE COUNTRY IMPORTS MORE THAN 80 PERCENT OF ITS ASBESTOS,CHROMIUM, COBALT, MAGNESIUM, PLATINUM, TIN, AND TUNGSTEN. THE UNITED STATES NOW PRODUCES ABOUT 65 PERCENTOF ITS PETROLEUM NEEDS, BUT NEW DOMESTIC DISCOVERIES TEND TO BE SMALL AND COSTLY TO RECOVER,ESPECIALLY IN THE GEOLOGICALLY COMPLEX MOUNTAIN REGIONS AND THE DEEP WATERS OF THE CONTINENTAL SHELF.AGRICULTURAL EXPORTS HAVE HELPED COMPENSATE FOR MINERAL IMPORTS, BUT THE PRICE IS HIGH. MORE THAN ATHIRD OF THE NATION'S TOPSOIL HAS BEEN LOST TO EROSION. GULLIES AND OTHER OBVIOUS SCARS COMMON IN THE1930S CAN NOW BE REPAIRED BY MODERN HEAVY MACHINERY, BUT SOIL LOSSES CAUSED BY LESS NOTICEABLE SHEETEROSION ARE STILL HIGH ON MORE THAN HALF THE NATION'S FARMLAND. MANY OBSERVERS HAVE ALSO EXPRESSEDCONCERN ABOUT THE RAPID CONVERSION OF PRIME CROPLAND TO URBAN AND OTHER NONFARM USES. DESPITE THESETRENDS, THE ENVIRONMENTAL PICTURE OF THE UNITED STATES IS NOT ALL BLEAK. BECAUSE OF GOVERNMENTREGULATIONS, WATER POLLUTION DIMINISHED CONSIDERABLY DURING THE 1970S; FORESTS ARE GROWING MORE RAPIDLYTHAN THEY ARE BEING CUT IN MOST REGIONS; AND SUBSTANTIAL AREAS HAVE BEEN SET ASIDE AS WILDERNESSPRESERVES AND NATIONAL PARKS. THE FEDERAL GOVERNMENT AND MOST OF THE STATES HAVE ADOPTED LAWS THATREQUIRE INVESTIGATION AND PUBLIC DISCLOSURE OF THE ENVIRONMENTAL IMPACT OF PROPOSED PROJECTS. THESEPROCEDURES HAVE HELPED TO INCREASE PUBLIC AWARENESS OF THE ENVIRONMENTAL COSTS OF CERTAIN ACTIVITIES. INTHE FUTURE THE QUESTIONS OF ACID RAIN, TOXIC WASTE DISPOSAL, WATER SUPPLY, AND CLIMATE CHANGE WILLCONTINUE TO BE MAJOR NATIONAL ENVIRONMENTAL ISSUES. POPULATION THE POPULATION OF THE UNITED

STATES IS HIGHLY MOBILE. IN THE 1980S AND EARLY 1990S REDISTRIBUTION FROM THE NORTH CENTRAL ANDNORTHEAST STATES TO THE SOUTH AND WEST CONTINUED TO BE A MAJOR TREND, AS THE AMERICAN POPULATIONBECAME INCREASINGLY DIVERSE IN ETHNIC COMPOSITION, CHARACTERISTICS, LANGUAGE, AND RELIGION.ACCORDING TO THE 1990 CENSUS, THE RESIDENT POPULATION OF THE UNITED STATES WAS 248,709,873. THE POPULATIONGREW BY 22,164,068 PEOPLEUOR 9.8 PERCENTUDURING THE DECADE FROM 1980 TO 1990. THIS INCREASE WASNOT EVENLY DISTRIBUTED: ABOUT 12 MILLION, OR 54.3 PERCENT OF THE GROWTH, OCCURRED IN THE STATESOF CALIFORNIA, TEXAS, AND FLORIDA. THE 1995 ESTIMATED POPULATION OF THE UNITED STATES IS263,437,000. ANOTHER TREND EVIDENT DURING THE 1980S WAS THAT ALTHOUGH URBAN AREAS GREW AT A SOMEWHATHIGHER RATE THAN RURAL AREAS, GROWTH RATES WERE LOW IN SOME OF THE LARGEST METROPOLITAN AREAS, AND THEPOPULATION OF A NUMBER OF MAJOR CITIESUSUCH AS CHICAGO, PHILADELPHIA, AND DETROITUDECREASEDSUBSTANTIALLY FROM 1980 TO 1990. ETHNIC COMPOSITION THE UNITED STATES IS BECOMING A MORE DIVERSESOCIETY RACIALLY AND ETHNICALLY. WHILE THE TOTAL U.S. POPULATION INCREASED BY 9.8 PERCENT BETWEEN1980 AND 1990 AND BY AN ESTIMATED 2.6 PERCENT BETWEEN 1990 AND 1992, THE BLACK POPULATION GREW BY14.2 PERCENT, FROM 26.7 MILLION IN 1980 TO 30.5 MILLION IN 1990 AND HAD REACHED AN ESTIMATED 31.4MILLION BY 1992. PERSONS OF HISPANIC ORIGIN, WHO MAY BE OF ANY RACE, INCREASED BY 53 PERCENT, FROM14.6 MILLION IN 1980 TO 22.4 MILLION IN 1990 AND INCREASED BY AN ESTIMATED 8.4 PERCENT TO 24.2MILLION BETWEEN 1990 AND 1992. THE NATIVE AMERICAN POPULATION, INCLUDING INUIT (ESKIMO), AND ALEUT,ALSO INCREASED, FROM 1.4 MILLION IN 1980 TO 2.1 MILLION IN 1990; THE POPULATION GREW MORE THAN 3PERCENT BETWEEN 1990 AND 1992, REACHING 2.13 MILLION. THE NUMBER OF ASIANS AND PACIFIC ISLANDERSWAS 7.5 MILLION, DOUBLE THE 1980 FIGURE OF 3.7 MILLION; BY 1992 THE NUMBER HAD REACHED 8.2 MILLION.AS A PERCENTAGE OF THE COUNTRY'S POPULATION, THE WHITE MAJORITY WAS REPORTED AS REDUCED SOMEWHAT

BETWEEN THE 1970S AND EARLY 1990S BOTH BY MIGRATION FROM ASIA, LATIN AMERICA, AND OTHER AREASAND BY HIGHER POPULATION GROWTH RATES AMONG BLACKS. DURING MUCH OF ITS HISTORY, THE UNITED STATES HADAN OFFICIAL POLICY OF ADMITTING MORE EUROPEAN IMMIGRANTS THAN ASIAN, AFRICAN, AND LATIN AMERICANIMMIGRANTS. CHANGES WERE MADE IN IMMIGRATION POLICY DURING THE 1970 S THAT RESULTED IN LARGENUMBERS OF NON-EUROPEAN IMMIGRANTS ENTERING THE UNITED STATES. THIS IN TURN ADDED NEW CULTURALDIMENSIONS TO AMERICAN LIFE. CENSUS FIGURES REPORTED FOR 1990 SHOWED THAT WHITES CONSTITUTED ABOUT 83.9PERCENT OF THE U.S. POPULATION; BLACKS, 12.3 PERCENT; NATIVE AMERICANS, 0.8 PERCENT; AND ASIANS ANDPACIFIC ISLANDERS, 3 PERCENT. HISPANICS, WHO MAY ALSO BE COUNTED AMONG OTHER GROUPS, MADE UP 9PERCENT OF THE POPULATION. AN UNKNOWN NUMBER OF UNDOCUMENTED IMMIGRANTS RESIDED IN THE UNITED STATES,MANY OF WHOM WERE NOT INCLUDED IN THESE CENSUS FIGURES. ACCORDING TO THE 1990 CENSUS, THE LARGESTGROUP, ABOUT 58 MILLION AMERICANS, WAS PARTLY OR SOLELY OF GERMAN ANCESTRY. IRISH ANCESTRY WASREPORTED BY 38.7 MILLION AMERICANS, AND ENGLISH ANCESTRY BY ANOTHER 32.7 MILLION. POPULATIONCHARACTERISTICS: STRUCTURE THE DIVERSE CHARACTERISTICS OF THE UNITED STATES POPULATION CAN BEST BEUNDERSTOOD BY EXAMINING ITS STRUCTURE AND SPATIAL DISTRIBUTION. A CLOSE LOOK AT THE AGESTRUCTURE OF THE POPULATION, FOR INSTANCE, REVEALS THAT THE UNITED STATES IS EXPERIENCING A DECLINE INCHILDREN AS A PERCENTAGE OF THE POPULATION, AND AN INCREASE IN THE PORTION OF THE POPULATION COMPOSEDOF YOUNG ADULTS AND THE ELDERLY. ALTHOUGH STILL INCREASING TO 60 MILLION, THE PORTION OF THEPOPULATION AGED 14 AND YOUNGER DECREASED BY ABOUT 0.8 PERCENTAGE POINTS FROM 1970 TO 1992. THE SHAREOF PEOPLE AGED 25 TO 34 INCREASED BY 0.6 PERCENTAGE POINTS DURING THE SAME PERIOD. THE NUMBER OFPEOPLE OF AGE 65 AND OLDER GREW 55.6 PERCENT, TO

31.1 MILLION, FROM 1970 TO 1990. THE MEDIAN AGEOF THE U.S. POPULATION REPORTED IN 1990 WAS 32.9 YEARS, SHOWING AN INCREASE OVER THE 30 YEARSREPORTED IN 1980. BY 1992 THE AVERAGE AGE HAD GROWN TO 33.4 YEARS. BY RACE AND ETHNIC GROUP, THECOUNTRY'S WHITE POPULATION IN 1990 WAS OLDEST, WITH A MEDIAN AGE OF 34.4 YEARS. ASIANS AND PACIFICISLANDERS CONSTITUTED THE SECOND OLDEST GROUP, WITH A MEDIAN AGE OF 29.8 YEARS; FOLLOWED BY BLACKS, WITH AMEDIAN AGE OF 28.1 YEARS. PEOPLE OF HISPANIC ORIGIN HAD A MEDIAN AGE OF 25.5 YEARS IN 1990. BASEDON THE ESTIMATED FERTILITY RATE FOR 1990, WOMEN IN THE UNITED STATES GIVE BIRTH TO AN AVERAGE OF 1.9CHILDREN DURING THEIR CHILDBEARING YEARS (BETWEEN THE AGES OF 15 AND 44). ALTHOUGH THIS WASSOMEWHAT BELOW THE RATE OF 2.1 CHILDREN PER WOMAN NECESSARY TO MAINTAIN THE SAME POPULATION LEVELINDEFINITELY, GROWTH OF THE U.S. POPULATION WELL INTO THE 21ST CENTURY IS NEVERTHELESS ASSURED, DUETO IMMIGRATION. THE ESTIMATED ANNUAL RATE OF INCREASE FOR THE U.S. POPULATION WAS ABOUT 0.1 PERCENTIN BOTH 1990 AND 1991; DURING THE SO-CALLED BABY BOOM FROM 1947 TO 1961, THE ANNUAL RATE OFINCREASE RANGED FROM 1.5 TO 2 PERCENT. THE STRUCTURE OF THE AMERICAN FAMILY CONTINUES TO CHANGE INRESPONSE TO SOCIAL AND ECONOMIC PRESSURES. BETWEEN 1970 AND 1990, FOR EXAMPLE, THE MEDIAN AGE AT FIRSTMARRIAGE ROSE FROM 22.5 TO 25.5 YEARS AMONG MEN AND FROM 20.6 TO 23.7 YEARS AMONG WOMEN. IN 1980, 50PERCENT OF MEN ENTERED THEIR FIRST MARRIAGES BETWEEN THE AGES OF 20 AND 24; BY 1988 THATPROPORTION HAD DROPPED TO 38.7 PERCENT, WHILE THE SHARE OF FIRST MARRIAGES AMONG MEN AGED 25-34 ROSE FROM33.2 PERCENT TO 47.7 PERCENT. AMONG WOMEN THE DECLINE IN THE PROPORTION OF FIRST MARRIAGESBEFORE AGE 20 WAS PARTICULARLY STRIKING: FROM 30.4 PERCENT IN 1980 TO 17.7 PERCENT IN 1988. AS MOREADULTS ARE POSTPONING MARRIAGE, OR NOT MARRYING AT ALL, SO ARE MORE ADULTS ENDING THEIR MARRIAGES

THROUGHDIVORCE. AS THE ANNUAL MARRIAGE RATE PER 1000 POPULATION DECREASED FROM 10.8 TO 9.7 BETWEEN 1970AND 1990, THE DIVORCE RATE ROSE FROM 3.5 TO 4.7; AFTER REACHING A PEAK OF 5.3 IN 1981, HOWEVER, THEANNUAL DIVORCE RATE ACTUALLY DECLINED DURING THE REMAINDER OF THE 1980S. THE NUMBER OF UNMARRIEDCOUPLES AMONG THE TOTAL U.S. POPULATION APPROXIMATELY TRIPLED BETWEEN 1970 AND 1980, TO ANESTIMATED 1.56 MILLION HOUSEHOLDS SHARED BY TWO UNRELATED ADULTS (WITH OR WITHOUT CHILDREN) OF OPPOSITESEX; BY 1991 THE NUMBER EXCEEDED 3 MILLION. OF THE NATION'S 94.3 MILLION HOUSEHOLDS IN 1991,MARRIED COUPLES (WITH OR WITHOUT CHILDREN) ACCOUNTED FOR 52.1 MILLION; THERE WERE 23.6 MILLIONSINGLE-PERSON HOUSEHOLDS, AN INCREASE OF 242 PERCENT SINCE 1970. ONE SIGNIFICANT CHARACTERISTIC OF THEU.S. POPULATION HAS BEEN AN EXTRAORDINARY INCREASE IN THE NUMBER OF BIRTHS TO UNMARRIED WOMEN.BIRTHS AMONG ALL UNMARRIED WOMEN REPRESENTED 11 PERCENT OF ALL BIRTHS IN 1970; BY 1991 THE OVERALLSHARE HAD GROWN TO 30 PERCENT. OF THE 36 MILLION FAMILIES WITH CHILDREN UNDER AGE 18 IN 1993, 69.8PERCENT WERE HEADED BY TWO-PARENT GROUPS. OF ONE-PARENT HOMES, 85.7 PERCENT WERE HEADED BY THEMOTHER. BECAUSE WOMEN MAINTAINING FAMILIES TENDED TO HAVE CONSIDERABLY LOWER INCOMES THAN THEIR MALECOUNTERPARTS, THEIR FAMILIES MADE UP A DISPROPORTIONATE SHARE OF THE POOR POPULATION IN THE UNITEDSTATES. POPULATION CHARACTERISTICS: SPATIAL DISTRIBUTION TRENDS IN THE SPATIAL DISTRIBUTION OFTHE U.S. POPULATION CONTINUED TO BE UNEVEN DURING THE 1980S AND EARLY 1990S, AS ABOVE-AVERAGEGROWTH OCCURRED IN THE SOUTH AND WEST AT THE EXPENSE OF THE NORTH CENTRAL AND NORTHEAST STATES. EVERYSTATE IN THE WEST (EXCEPT WYOMING) GREW FASTER BETWEEN 1990 AND 1993 THAN THE U.S. AVERAGE. THESOUTH ALSO SHOWED ABOVE-AVERAGE GROWTH, PARTICULARLY IN TEXAS AND THE SOUTH ATLANTIC

STATES; EXCEPTIONSTO THIS PATTERN WERE WEST VIRGINIA AND THE DISTRICT OF COLUMBIA, BOTH OF WHICH LOST POPULATION.BETWEEN 1980 AND 1990 THE POPULATION OF THE WEST INCREASED BY 22 PERCENT AND THE POPULATION OF THESOUTH BY 13.4 PERCENT. GROWTH CONTINUED IN THE EARLY 1990S. IN 1990 THE POPULATION WAS DISTRIBUTEDAS FOLLOWS: 50.8 MILLION PEOPLE IN THE NORTHEAST, 59.7 MILLION IN THE NORTH CENTRAL STATES,85.4 MILLION IN THE SOUTH, AND 52.8 MILLION IN THE WEST. BY 1993 THE ESTIMATED POPULATIONDISTRIBUTION WAS NORTHEAST, 51.4 MILLION; MIDWEST, 61.1 MILLION; SOUTH, 89.4 MILLION; AND WEST, 56 MILLION.THE AVERAGE POPULATION DENSITY FOR THE UNITED STATES AS A WHOLE WAS ABOUT 26 PERSONS PER SQ KM(66 PER SQ MI) IN 1990. THIS REPRESENTS A SUBSTANTIAL INCREASE OVER THE AVERAGE DENSITIES OF 1.7PEOPLE PER SQ KM (4.5 PER SQ MI) IN 1790; 3 PER SQ KM (7.9 PER SQ MI) IN 1850; 9.9 PER SQ KM(25.6 PER SQ MI) IN 1900; AND 19.5 PER SQ KM (50.6 PER SQ MI) IN 1950. AMONG THE TOTAL POPULATION OFTHE UNITED STATES, THE NONWHITE AND HISPANIC- ORIGIN POPULATIONS HAVE REMAINED HIGHLY CONCENTRATED.IN 1995, FOR EXAMPLE, IT WAS ESTIMATED THAT BLACKS CONSTITUTED MORE THAN ONE-FIFTH OF THE POPULATIONIN EIGHT STATES: MISSISSIPPI, NEW YORK, SOUTH CAROLINA, LOUISIANA, GEORGIA, ALABAMA, MARYLAND, ANDNORTH CAROLINA. IN THE DISTRICT OF COLUMBIA IN 1990, 66 PERCENT OF THE POPULATION WAS BLACK. ABOUT46 PERCENT OF THE NATIVE AMERICANS LIVED IN THE WEST, AND ALMOST ALL OF THE INUIT AND ALEUTSLIVED IN ALASKA. NEARLY HALF OF THE 7.3 MILLION ASIANS AND PACIFIC ISLANDERS LIVED IN CALIFORNIA ANDHAWAII. ABOUT 65 PERCENT OF THE 22.4 MILLION PEOPLE OF HISPANIC ORIGIN RESIDED IN CALIFORNIA,TEXAS, NEW YORK, AND FLORIDA. FOR MANY DECADES BEFORE 1970, THE URBAN POPULATION GREW AT A RAPIDPACE. IN THE 1970S THE TREND SEEMED TO BE CHANGING. DATA FROM THE 1980 CENSUS SHOWED THAT THE PROPORTIONOF THE U.S. POPULATION LIVING IN URBAN AREAS

(DEFINED AS DENSELY POPULATED AREAS AND PLACES OF2500 OR MORE INHABITANTS OUTSIDE DENSELY POPULATED AREAS) GREW ONLY BY ABOUT 0.1 PERCENT BETWEEN1970 AND 1980, THE SMALLEST TEN-YEAR GAIN IN U.S. HISTORY. ACCORDING TO THE 1990 CENSUS, THE PACE OFURBAN GROWTH INCREASED BETWEEN 1980 AND 1990, AS THE TOTAL URBAN POPULATION ROSE TO A NEW HIGHWITH AN INCREASE OF 13.5 PERCENT OVER 1980. ONLY ONCE IN THE HISTORY OF THE UNITED STATES HAS THEURBAN PROPORTION OF THE POPULATION DECLINEDUBY 0.1 PERCENT BETWEEN 1810 AND 1820. IN 1990 URBANDWELLERS MADE UP ABOUT 75.2 PERCENT OF THE U.S. POPULATION, OR SOME 187.1 MILLION PEOPLE. RURALRESIDENTS MADE UP 24.8 PERCENT OF THE POPULATION, OR ABOUT 61.7 MILLION PEOPLE. THE UNITED STATESCONTINUED TO BE A PREDOMINANTLY URBAN NATION, AND THERE WAS NO EVIDENCE OF A SIGNIFICANT MIGRATIONOF URBAN DWELLERS BACK TO FARMS. APPROXIMATELY 1.9 PERCENT OF THE TOTAL U.S. POPULATION, ABOUT 4.6MILLION PEOPLE, LIVED ON FARMS IN 1990, A DECLINE OF 12.1 PERCENT FROM 1980. COMPUTER,ELECTRONIC DEVICE THAT CAN RECEIVE A SET OF INSTRUCTIONS, OR PROGRAM, AND THEN CARRY OUT THIS PROGRAM BYPERFORMING CALCULATIONS ON NUMERICAL DATA OR BY COMPILING AND CORRELATING OTHER FORMS OF INFORMATION.THE MODERN WORLD OF HIGH TECHNOLOGY COULD NOT HAVE COME ABOUT EXCEPT FOR THE DEVELOPMENT OF THECOMPUTER. DIFFERENT TYPES AND SIZES OF COMPUTERS FIND USES THROUGHOUT SOCIETY IN THE STORAGE ANDHANDLING OF DATA, FROM SECRET GOVERNMENTAL FILES TO BANKING TRANSACTIONS TO PRIVATE HOUSEHOLDACCOUNTS. COMPUTERS HAVE OPENED UP A NEW ERA IN MANUFACTURING THROUGH THE TECHNIQUES OF AUTOMATION,AND THEY HAVE ENHANCED MODERN COMMUNICATION SYSTEMS. THEY ARE ESSENTIAL TOOLS IN ALMOST EVERYFIELD OF RESEARCH AND APPLIED TECHNOLOGY, FROM CONSTRUCTING MODELS OF THE UNIVERSE TO PRODUCINGTOMORROW'S WEATHER REPORTS, AND THEIR USE HAS IN ITSELF OPENED UP NEW AREAS OF CONJECTURE.DATABASE SERVICES AND COMPUTER NETWORKS MAKE AVAILABLE A GREAT VARIETY OF INFORMATION SOURCES. THE SAMEADVANCED TECHNIQUES ALSO MAKE POSSIBLE INVASIONS OF PRIVACY AND OF RESTRICTED INFORMATIONSOURCES, BUT COMPUTER CRIME HAS BECOME ONE OF THE

MANY RISKS THAT SOCIETY MUST FACE IF IT WOULD ENJOYTHE BENEFITS OF MODERN TECHNOLOGY. TYPES OF COMPUTERS TWO MAIN TYPES OF COMPUTERS ARE IN USETODAY, ANALOG AND DIGITAL, ALTHOUGH THE TERM COMPUTER IS OFTEN USED TO MEAN ONLY THE DIGITAL TYPE.ANALOG COMPUTERS EXPLOIT THE MATHEMATICAL SIMILARITY BETWEEN PHYSICAL INTERRELATIONSHIPS INCERTAIN PROBLEMS, AND EMPLOY ELECTRONIC OR HYDRAULIC CIRCUITS (SEE FLUIDICS) TO SIMULATE THE PHYSICALPROBLEM. DIGITAL COMPUTERS SOLVE PROBLEMS BY PERFORMING SUMS AND BY DEALING WITH EACH NUMBER DIGITBY DIGIT. INSTALLATIONS THAT CONTAIN ELEMENTS OF BOTH DIGITAL AND ANALOG COMPUTERS ARE CALLEDHYBRID COMPUTERS. THEY ARE USUALLY USED FOR PROBLEMS IN WHICH LARGE NUMBERS OF COMPLEX EQUATIONS,KNOWN AS TIME INTEGRALS, ARE TO BE COMPUTED. DATA IN ANALOG FORM CAN ALSO BE FED INTO A DIGITALCOMPUTER BY MEANS OF AN ANALOG- TO-DIGITAL CONVERTER, AND THE SAME IS TRUE OF THE REVERSE SITUATION(SEE DIGITAL- TO-ANALOG CONVERTER). ANALOG COMPUTERS THE ANALOG COMPUTER IS AN ELECTRONIC ORHYDRAULIC DEVICE THAT IS DESIGNED TO HANDLE INPUT IN TERMS OF, FOR EXAMPLE, VOLTAGE LEVELS ORHYDRAULIC PRESSURES, RATHER THAN NUMERICAL DATA. THE SIMPLEST ANALOG CALCULATING DEVICE IS THE SLIDERULE, WHICH EMPLOYS LENGTHS OF SPECIALLY CALIBRATED SCALES TO FACILITATE MULTIPLICATION, DIVISION,AND OTHER FUNCTIONS. IN A TYPICAL ELECTRONIC ANALOG COMPUTER, THE INPUTS ARE CONVERTED INTOVOLTAGES THAT MAY BE ADDED OR MULTIPLIED USING SPECIALLY DESIGNED CIRCUIT ELEMENTS. THE ANSWERS ARECONTINUOUSLY GENERATED FOR DISPLAY OR FOR CONVERSION TO ANOTHER DESIRED FORM. DIGITAL COMPUTERSEVERYTHING THAT A DIGITAL COMPUTER DOES IS BASED ON ONE OPERATION: THE ABILITY TO DETERMINE IF ASWITCH, OR GATE, IS OPEN OR CLOSED. THAT IS, THE COMPUTER CAN RECOGNIZE ONLY TWO STATES IN ANY OFITS MICROSCOPIC CIRCUITS: ON OR OFF, HIGH VOLTAGE OR LOW VOLTAGE, ORUIN THE CASE OF NUMBERSU0 OR1. THE SPEED AT WHICH THE COMPUTER PERFORMS THIS SIMPLE ACT, HOWEVER, IS WHAT MAKES IT A MARVEL

OF MODERN TECHNOLOGY. COMPUTER SPEEDS ARE MEASURED IN MEGAHERTZ, OR MILLIONS OF CYCLES PERSECOND. A COMPUTER WITH A CLOCK SPEED OF 33 MHZ IS CAPABLE OF EXECUTING 33 MILLION DISCRETE OPERATIONSEACH SECOND. BUSINESS MICROCOMPUTERS CAN PERFORM 60 TO 100 MILLION OPERATIONS PER SECOND, ANDSUPERCOMPUTERS USED IN RESEARCH AND DEFENSE APPLICATIONS ATTAIN SPEEDS OF BILLIONS OF CYCLES PERSECOND. DIGITAL COMPUTER SPEED AND CALCULATING POWER ARE FURTHER ENHANCED BY THE AMOUNT OF DATAHANDLED DURING EACH CYCLE. IF A COMPUTER CHECKS ONLY ONE SWITCH AT A TIME, THAT SWITCH CAN REPRESENTONLY TWO COMMANDS OR NUMBERS; THUS ON WOULD SYMBOLIZE ONE OPERATION OR NUMBER, AND OFF WOULDSYMBOLIZE ANOTHER. BY CHECKING GROUPS OF SWITCHES LINKED AS A UNIT, HOWEVER, THE COMPUTER INCREASES THENUMBER OF OPERATIONS IT CAN RECOGNIZE AT EACH CYCLE. FOR EXAMPLE, A COMPUTER THAT CHECKS TWOSWITCHES AT ONE TIME CAN REPRESENT FOUR NUMBERS (0 TO 3) OR CAN EXECUTE ONE OF FOUR INSTRUCTIONS ATEACH CYCLE, ONE FOR EACH OF THE FOLLOWING SWITCH PATTERNS: OFF-OFF (0); OFF- ON (1); ON-OFF (2); ORON-ON (3). HISTORY THE FIRST ADDING MACHINE, A PRECURSOR OF THE DIGITAL COMPUTER, WASDEVISED IN 1642 BY THE FRENCH PHILOSOPHER AND MATHEMATICIAN BLAISE PASCAL. THIS DEVICE EMPLOYED ASERIES OF TEN-TOOTHED WHEELS, EACH TOOTH REPRESENTING A DIGIT FROM 0 TO 9. THE WHEELS WERE CONNECTED SOTHAT NUMBERS COULD BE ADDED TO EACH OTHER BY ADVANCING THE WHEELS BY A CORRECT NUMBER OF TEETH. INTHE 1670S THE GERMAN PHILOSOPHER AND MATHEMATICIAN GOTTFRIED WILHELM LEIBNIZ IMPROVED ON THISMACHINE BY DEVISING ONE THAT COULD ALSO MULTIPLY. THE FRENCH INVENTOR JOSEPH MARIE JACQUARD , INDESIGNING AN AUTOMATIC LOOM, USED THIN, PERFORATED WOODEN BOARDS TO CONTROL THE WEAVING OF COMPLICATEDDESIGNS. DURING THE 1880S THE AMERICAN STATISTICIAN HERMAN HOLLERITH CONCEIVED THE IDEA OF USINGPERFORATED CARDS, SIMILAR TO JACQUARD'S BOARDS,

FOR PROCESSING DATA. EMPLOYING A SYSTEM THAT PASSEDPUNCHED CARDS OVER ELECTRICAL CONTACTS, HE WAS ABLE TO COMPILE STATISTICAL INFORMATION FOR THE1890 U.S. CENSUS. THE ANALYTICAL ENGINE ALSO IN THE 19TH CENTURY, THE BRITISH MATHEMATICIANAND INVENTOR CHARLES BABBAGE WORKED OUT THE PRINCIPLES OF THE MODERN DIGITAL COMPUTER. HECONCEIVED A NUMBER OF MACHINES, SUCH AS THE DIFFERENCE ENGINE, THAT WERE DESIGNED TO HANDLECOMPLICATED MATHEMATICAL PROBLEMS. MANY HISTORIANS CONSIDER BABBAGE AND HIS ASSOCIATE, THE BRITISHMATHEMATICIAN AUGUSTA ADA BYRON (LADY LOVELACE, 1815-52), THE DAUGHTER OF THE ENGLISH POET LORD BYRON,THE TRUE INVENTORS OF THE MODERN DIGITAL COMPUTER. THE TECHNOLOGY OF THEIR TIME WAS NOT CAPABLE OFTRANSLATING THEIR SOUND CONCEPTS INTO PRACTICE; BUT ONE OF THEIR INVENTIONS, THE ANALYTICAL ENGINE,HAD MANY FEATURES OF A MODERN COMPUTER. IT HAD AN INPUT STREAM IN THE FORM OF A DECK OF PUNCHEDCARDS, A STORE FOR SAVING DATA, A MILL FOR ARITHMETIC OPERATIONS, AND A PRINTER THAT MADE APERMANENT RECORD.