Chapter 4 Computer Memory EET 450 - Advanced Digital Chapter 4 Computer Memory

Memory Primary and Secondary Storage Primary is part of main memory at one point, DISK, DRUM, or CORE memory was used. Secondary is an antiquated view of a system, but usually refers to mass storage. Old technology included the use of punch card, tape or DISK/DRUM memory

Memory Main memory in modern PC’s uses a volatile type of memory Semiconductor memory is the rule Non-Volatile memory is used for special purpose functions within the PC BIOS CMOS - is battery backup version on non-volatile memory EEPROM or FLASH memory

Measurement Capacity of memory is based on the amount of digital information that can be stored. Bits/ Bytes/ Nibbles Words Double Words Quad Words Line

Memory is used in modern based on GRANULARITY the smallest amount of memory that can be addressed Increased bus widths have INCREASED the size of the smallest granule accessed Pentium/Pentium Pro use eight-byte modules

Technologies Random Access Memory Dynamic Memory Data In Data Out

Static Memory - referred to as SRAM Read Only Memory ROM Mask ROM - older bios chips PROM - Programmable EPROM - Erasable Programmable ROM EEPROM - Electrically Erasable PROM Flash Memory

Where’s the Memory Memory uses in a PC L1 L2 C A H E C A H E Main Memory CPU Mass Storage Cache

Memory Use Storage of program information Storage of BOOT information program and settings Storage of DATA

Logical Organization Real Mode Memory - legacy of the 8086 processor 1 Mbyte address space base memory

Logical Organization Protected Mode memory Lower Memory Provides the entire address space of the processor 4 Gbytes + Lower Memory Legacy stuff again < 640k - conventional DOS memory

BIOS Data Area Upper Memory Vector Table - lower 1k the upper 384k of memory address space top 32K - ROM Bios memory

High Memory Frame Buffer memory 64kB+16 bytes above Upper memory address line A20 allows this a function of binary round-off Frame Buffer memory Part of video memory

Shadow Memory Provides solution to slower ROM memory providing BIOS functions. ROM memory is slower than fast RAM for a variety of reasons - bus width, intrinsic speed, etc. BIOS is ‘shadowed’ into RAM at boot time, allowing faster access to these functions. Other ROM memory - controller cards, video, etc may be shadowed.

Cache Memory provides the speed interface between slower memory/devices and the faster memory/devices

System Resource Memory Memory allocated by ‘heaps’ older OS problems with release of memory on program exit.

Unified Memory Architecture UMA maps main memory into video display address space

Performance Memory Speed based on access speed of integrated circuits -12 is 120 nS memory, Must have faster memory than called for by processor speed. Bus interface may be the problem.

Caching Cache Size - 1k 256 k most favored Note: Celeron processor suffered severe performance penalties by failing to include Cache memory

Cache Performance four sections show cache hits for access to store a single line - one for each transfer 1-1-1-1 would be best

Cache Mapping Direct Mapped Full associative set-associative CACHE mapped to block of memory Full associative CACHE can be for any block of memory very costly - complex set-associative sections of CACHE are direct mapped.

Synchronous Burst Ram - SRAM (note acronym conflict) Burst-Mode Caches blocks of data at a time Synchronous Burst Ram - SRAM (note acronym conflict) Pipelined burst SRAM

Cache consistency Write-through Write-back

Memory Types Static Column Ram Page-Mode RAM (FP) Extended Data Out Memory (EDO) Burst EDO DRAM Synchronous DRAM Enhanced DRAM Cached DRAM

Rambus DRAM Multibank DRAM PC100 RAM PC166/266/333/400 etc.

Memory Packages DIP SIPP SIMM 30 pin 72 pin DIMM 168 pin

Assignment Complete Chapter on memory Review ‘Tom’s Hardware Guide: Ram Guide. Research ‘other’ RAM packages that may be available.