MEMORY:

ALSO CALLED MAIN MEMORY. THE WORKING SPACE USED BY THE COMPUTER TO HOLD THE PROGRAM THAT IS CURRENTLY RUNNING, ALONG WITH THE DATA IT NEEDS, AND TO RUN PROGRAMS AND PROCESS DATA. THE MAIN MEMORY IS BUILT FROM RAM CHIPS. THE AMOUNT OF MEMORY AVAILABLE DETERMINES THE SIZE OF PROGRAMS THAT CAN BE RUN, AND WHETHER MORE THAN ONE PROGRAM CAN BE RUN AT ONCE. MAIN MEMORY IS TEMPORARY, AND IS LOST WHEN THE COMPUTER IS TURNED OFF. IT IS DISTINGUISHED FROM MORE PERMANENT INTERNAL MEMORY ( ROM ) WHICH CONTAINS THE COMPUTERS ESSENTIAL PROGRAMS, AND STORAGE ( THE DISK AND TAPES WHICH ARE USED TO STORE DATA ).

RAM RANDOM ACCESS MEMORY:

THE WORKING MEMORY OF THE COMPUTER. RAM IS THE MEMORY USED FOR STORING DATA TEMPORARILY WHILE WORKING ON IT, RUNNING APPLICATION PROGRAMS, ETC.. RANDOM ACCESS REFERS TO THE FACT THAT ANY AREA OF RAM CAN BE ACCESSED DIRECTLY AND IMMEDIATELY, IN CONTRAST TO OTHER MEDIA SUCH AS MAGNETIC TAPE WHERE THE TAPE MUST BE WOUND TO THE POINT WHERE THE DATA IS. RAM IS CALLED VOLATILE MEMORY; INFORMATION IN RAM WILL DISAPPEAR IF THE POWER IS SWITCHED OFF BEFORE IT IS SAVED TO A DISK. THERE IS ALSO A FORM OF NON-VOLATILE RAM, WHICH MUST BE CONTINUALLY ENERGIZED BY A BATTERY TO MAINTAIN ITS CONTENT. THE MOST COMMON FORM OF RAM IS BUILT FROM SEMICONDUCTOR INTEGRATED CIRCUITS.

VIRTUAL MEMORY :

AN IMAGINARY MEMORY AREA SUPPOTED BY SOME OPERATING SYSTEMS IN CONJUNCTION WITH THE HARDWARE. YOU CAN THINK OF VIRTUAL MEMORY AS AN ALTERNATE SET OF MEMORY ADDRESSES. PROGRAMS USE THESE VIRTUAL ADDRESSES RATHER THAN REAL ADDRESSES TO STORE INSTRUCTIONS AND DATA. WHEN THE PROGRAM IS ACTUALLY EXECUTED, THE VIRTUAL ADDRESSES ARE CONVERTED INTO REAL MEMORY ADDRESSES.

THE PURPOSE OF VIRTUAL MEMORY IS TO ENLARGE THE ADDRESS SPACE, THE SET OF ADDRESSES A PROGRAM CAN UTILIZE. FOR AN EXAMPLE, VIRTUAL MEMORY MIGHT CONTAIN TWICE AS MANY ADDRESSES AS MAIN MEMORY. A PROGRAM USING ALL OF VIRTUAL MEMORY, THEREFORE WOULD NOT BE ABLE TO FIT IN MAIN MEMORY ALL AT ONCE. NEVERTHELESS, THE COMPUTER COULD EXECUTE SUCH A PROGRAM BY COPYING INTO MAIN MEMORY THOSE PORTIONS OF THE PROGRAM NEEDED AT ANY GIVEN POINT DURING EXECUTION.

THE PROCESS OF TRANSLATING VIRTUAL ADDRESSES INTO REAL ADDRESSES IS CALLED MAPPING. THE COPYING OF VIRTUAL PAGES FROM DISK TO MAIN MEMORY IS KNOWN AS PAGING OR SWAPPING.

HOW WINDOWS DIVIDES MEMORY :

CONVENTIONAL MEMORY :

THE FIRST 640K OF SYSTEM MEMORY. USED BY THE OPERATING SYSTEM KERNELS AND STANDARD DOS PROGRAMS, DEVICE DRIVERS, AND TSRs.

UPPER MEMORY :

THE UPPER 384KB OF THE FIRST MEGABYTE OF MEMORY, LOCATED RIGHT ABOVE CONVENTIONAL MEMORY. RESERVED ( AND SOME TIMES REFERED TO AS RESERVED MEMORY ) FOR THE SYSTEM BIOS AND DEVICE DRIVERS AND SPECIAL USES SUCH AS ROM SHADOWING. MAY EVEN BE REFERED TO AS EXPANDED MEMORY.

HIGH MEMORY :

THE FIRST 64K ( LESS 16 BYTES ) OF THE SECOND MEGABYTE OF MEMORY. ALTHOUGH ITS THE FIRST 64K OF EXTENDED MEMORY, IT CAN BE ACCESSED IN REAL MODE.

EXTENDED MEMORY :

ALL MEMORY ABOVE 1 MB. OR ANY MEMORY ABOVE THE HIGH MEMORY.

MEMORY DEFINITION KNOWLEDGE :

DIMM :

DUAL IN-LINE MEMORY MODULE, A SLIM CIRCUIT BOARD THAT HOLDS RAM CHIPS. THE BUS FROM A DIMM TO THE ACTUAL MEMORY CHIP IS A 64 BIT PATH. WITH DIMM, YOU CAN INSTALL MEMORY, ONE DIMM AT A TIME.

DRAM:

DYNAMIC RANDOM ACCESS MEMORY, A TYPE OF COMPUTER MEMORY THAT IS STORED IN CAPACITORS ON A CHIP AND REQUIRES A REFRESH SIGNAL TO BE SENT TO IT PERIODICALLY. MANY COMPUTERS HAVE DRAM CHIPS, BECAUSE THEY PROVIDE A LOT OF MEMORY AT A LOW COST.

DDR DRAM :

DOUBLE DATA RATE DRAM, A HIGH PERFORMANCE ALTERNATIVE TO DIRECT RDRAM.WORKS BY EFFECTIVELY DOUBLING THE CLOCK FREQUENCY WITHOUT INCREASING THE ACTUAL FREQUENCY.

DRD RAM :

DIRECT RAMBUS DRAM, BUS MASTERING TO 500 MBps IN BURST MODE. 20X INCREASE OVER DRAM.

EDO DRAM :

EXTENDED DATA OUT DRAM, A FAST DYNAMIC RAM CHIP. IT DOES NOT DEMAND THAT THE MEMORY COLUMN BE DEACTIVATED AND THE OUTPUT BUFFER TURNED OFF BEFORE THE NEXT DATA TRANSFER STARTS.

EDO RAM :

EXTENDED DATA OUT RAM, SAME AS EDO DRAM, A MEMORY CHIP USED MOSTLY WITH PENTIUM PROCESSORS, THAT ACCESSES DATA FASTER BY OVERLAPPING CYCLES OF DATA OUTPUT.

ED RAM :

ENHANCED DYNAMIC RAM, CACHE DRAM, PUTS SRAM INTO DRAM.

FPM DRAM :

FAST PAGE MODE DRAM, ACCESS TIMES OF 60ns OR 70ns, THE MEMORY MANAGEMENT UNIT READS DATA BY FIRST ACTIVATING THE APPROPRIATE ROW OF MEMORY ADDRESSES, ACTIVATING THE CORRECT COLUMN OF MEMORY ADDRESSES, VALIDATING THE DATA AND TRANSFERRING THE DATA BACK TO THE SYSTEM.

FRAM :

FERROELECTRIC RANDOM ACCESS MEMORY, NON VOLATILE SEMICONDUCTOR MEMORY GOOD FOR 10 YEARS.

RIMM :

THE MEMORY MODULE USED WITH RDRAM CHIPS. IT IS SIMILAR TO A DIMM PACKAGE BUT USES DIFFERENT PIN SETTINGS. THEY HAVE 184 PINS COMPARED TO DIMMs 168 PIN. BUT THEY USE THE SAME SOCKET SPECIFICATIONS AS A STANDARD DIMM. SYSTEMS CAN NOT USE RIMMs UNLESS BOTH BIOS AND THE CHIP SET SUPPORT IT. ALL RIMM CONNECTORS NEED TO BE POPULATED WITH EITHER RIMM MEMORY MODULE OR A C-RIMM TO INSURE THE ELECTRICAL INTEGRITY OF THE HIGH SPEED RAMBUS CHANNEL. IT IS SOMETIMES INCORRECTLY USED AS AN ACRONYM FOR RAMBUS INLINE MEMORY MODULE.

C - RIMM :

CONTINUITY RIMM, SINCE THERE CAN NOT BE ANY UNUSED RIMM SLOTS ON A MOTHERBOARD, A C-RIMM IS A SPECIAL MODULE USED TO FILL ANY UNUSED RIMM SLOTS. IT IS BASICALLY A RIMM MODULE WITHOUT ANY MEMORY CHIPS.

SD RAM :

SYNCHRONOUS DYNAMIC RANDOM ACCESS, HIGH SPEED DRAM THAT ADDS A SEPARATE CLOCK SIGNAL TO THE CONTROL SIGNALS. SDRAM CAN TRANSFER BURSTS OF NON-CONTIGUOUS DATA AT 100 MBYTES/SECOND, AND HAS AN ACCESS TIME OF 8-12 NANOSECONDS. IT COMES IN 64 BIT MODULES,168-PIN DIMMs.

PC 133 SDRAM

TRANSFERS DATA AT UP TO 1.6 GBps COMPARED WITH THE TO NOW SPEEDS OF UP TO 800 MBps. WITHOUT ANY CHANGES TO THE ENGINEERING OF THE MOTHERBOARD.

SGRAM :

SYNCHRONOUS GRAPHIC RANDOM ACCESS MEMORY, USED FOR GRAPHIC INTENSIVE OPERATIONS SUCH AS 3-D RENDERING AND DISPLAYING FULL MOTION VIDEO.

SIMM :

SINGLE IN-LINE MEMORY MODULE, A SLIM CIRCUIT BOARD THAT HOLDS A GROUP OF RAM CHIPS.THE BUS FROM A SIMM TO THE ACTUAL MEMORY CHIP IS 32 BITS WIDE. SIMMs MAY NEED TO BE INSTALLED IN MULTIPLES OF TWO OR FOUR.

SO DIMM :

SMALL OUTLINE DIMM, A SMALL VERSION OF A DIMM USED COMMONLY IN NOTEBOOK COMPUTERS. WHERE A FULL SIZE DIMM HAS 168 PINS AND SUPPORTS 64 BIT TRANSFERS, A SO DIMM HAS ONLY 72 PINS, WHICH SUPPORTS ONLY 32 BIT TRANSFERS, OR 144 PINS, WHICH SUPPORTS A FULL 64 BIT TRANSFER.

SRAM :

STATIC RANDOM ACCESS MEMORY, A KIND OF RANDOM ACCESS MEMORY THAT REQUIRES A CONSTANT SUPPLY OF POWER IN ORDER TO HOLD ITS CONTENT, BUT DOES NOT REQUIRE REFRESH CIRCUITRY AS DYNAMIC RAM DOES. EACH STATIC RAM BIT IS A FLIP-FLOP CIRCUIT MADE OF CROSS COUPLED INVERTERS; THE ACTIVATION OF TRANSISTORS CONTROLS THE FLOW OF CURRENT FROM ONE SIDE TO THE OTHER. UNLIKE READ ONLY MEMORY ( ROM ), SRAM WILL LOSE ITS CONTENT WHEN THE POWER IS SWITCHED OFF.STATIC RAM IS USUALLY FASTER THAN DYNAMIC RAM, BUT TAKES UP MORE SPACE AND USES MORE POWER. IT IS USED FOR THE PARTS OF A COMPUTER THAT REQUIRE HIGHEST SPEED, SUCH AS CACHE MEMORY.

SWAP :

TO REPLACE PAGES OR SEGMENTS OF DATA IN MEMORY. SWAPPING IS A USEFUL TECHNIQUE THAT ENABLES A COMPUTER TO EXECUTE PROGRAMS AND MANIPULATE DATA FILES LARGER THAN MAIN MEMORY. THE OPERATING SYSTEM COPIES AS MUCH DATA AS POSSIBLE INTO MAIN MEMORY, AND LEAVES THE REST ON THE DISK. WHEN THE OPERATING SYSTEM NEEDS DATA FROM THE DISK, IT EXCHANGES A PORTION OF DATA ( CALLED PAGES OR SEGMENT ) IN MAIN MEMORY WITH A PORTION OF DATA ON THE DISK.

VRAM :

VIDEO RANDOM ACCESS MEMORY, A KIND OF HIGH SPEED MEMORY USED FOR THE COMPUTERS DISPLAY. VRAM MUST BE FAST TO KEEP UP WITH THE SPEED AT WHICH THE SCREEN IS SCANNED. THE VRAM IN A PC IS ON A DISPLAY ADAPTER CARD. VRAM HAS TWO PORTS SO IT CAN SEND DATA FOR TEXT AND IMAGES TO MEMORY AND TO THE DISPLAY AT THE SAME TIME.

MEMORY CACHE :

IS A PORTION OF MEMORY MADE OF HIGH SPEED STATIC RAM ( SRAM ) INSTEAD OF THE SLOWER DYNAMIC RAM USED FOR MAIN MEMORY. MEMORY CACHE IS EFFECTIVE BECAUSE MOST PROGRAMS ACCESS THE SAME DATA OVER AND OVER. KEEPING ALL OF THIS INFORMATION IN THE FAST SRAM. ALLOWS THE COMPUTER TO AVOID ACCESSING THE SLOWER DRAM. DATA IS FIRST WRITTEN TO CACHE ON THE ASSUMPTION THAT IT WILL BE USED AGAIN SOON.

LEVEL 1 CACHE ( L1 )

ALSO CALLED PRIMARY CACHE, IS MEMORY CACHE THAT IS BUILT INTO THE CPU CHIP. A FAST TRANSFER SPEED FOR A MEMORY BUS. IT IS A SMALL FAST MEMORY AREA THAT WORKS TOGETHER WITH THE LEVEL 2 CACHE TO PROVIDE THE CPU MUCH FASTER ACCESS TO IMPORTANT AND OFTEN USED DATA.

LEVEL 2 CACHE ( L2 )

ALSO CALLED SECONDARY CACHE, IS A COLLECTION OF MEMORY CHIPS ON THE MOTHERBOARD. L2 CACHE IS A STATIC RAM SECONDARY MEMORY AREA WHICH IS SLOWER THAN L1 BUT FASTER THAN MAIN MEMORY. L1 AND L2 CACHE ARE USED TOGETHER.

LEVEL 3 CACHE ( L3 )

AS MORE AND MORE PROCESSORS BEGIN TO INCLUDE L2 CACHE INTO THEIR ARCHITECTURES, LEVEL 3 CACHE IS NOW THE NAME FOR THE EXTRA CACHE BUILT INTO MOTHERBOARDS BETWEEN THE MICROPROCESSOR AND THE MAIN MEMORY.

WHAT WAS ONCE L2 CACHE ON MOTHERBOARDS NOW BECOMES L3 CACHE WHEN USED WITH MICROPROCESSORS CONTAINING BUILT IN L2 CACHES.

WRITE THROUGH CACHE :

DATA IS WRITTEN TO MAIN MEMORY AT THE SAME TIME AS IT IS CACHES.

WRITE BACK CACHE :

DATA IS WRITTEN TO MAIN MEMORY ONLY WHEN IT IS FORCED OUT OF THE CACHE.