A+ Guide to Managing and Maintaining Your PC Fifth Edition Chapter 6 Managing Memory

2 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Types ROM – Read-Only Memory  Permanent – retains data even when power is off  System ROM BIOS, device ROM BIOS RAM – Read-write Memory  Volatile – losses data when power is off  CPU cache memory, main memory

3 A+ Guide to Managing and Maintaining Your PC, Fifth Edition EEPROM Electrically Erasable Programmable ROM – data can be erased under software control “Flash BIOS”

4 A+ Guide to Managing and Maintaining Your PC, Fifth Edition RAM Static RAM (SRAM) Dynamic RAM (DRAM) SpeedFaster Costmore expensive Sizemore space Simplicityno refreshConstant refresh UsageL1/L2/L3 cacheMain memory AddressingNoYes % of accesses90-95%5-10%

5 A+ Guide to Managing and Maintaining Your PC, Fifth Edition The Memory Controller Is normally integrated into the chipset (northbridge) Controls accesses to CPU caches and main memory  CPU caches: predicts and prefetches instructions and data  Main memory: specifies the memory address on the address bus Interfaces with processor and other devices

6 A+ Guide to Managing and Maintaining Your PC, Fifth Edition DRAM Refresh Operates every a few milliseconds A refresh circuit reads the contents of each memory cell, whether it is being used or not The reading action itself refreshes the memory contents

7 A+ Guide to Managing and Maintaining Your PC, Fifth Edition DRAM Memory Accesses Asynchronous accesses  Not synchronized to the system clock  For lower-speed memory buses (< 66 MHz) Synchronous accesses  Synchronized to the system clock  Much faster than asynchronous DRAM  For higher-speed memory systems of newer PCs

8 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Representative Dynamic RAM Technologies Asynchronous DRAM  EDO (Extended Data Out): Pentium /486 SDRAM (Synchronous DRAM)  Regular SDRAM  DDR (Double-data Rate) SDRAM: doubles the bandwidth by transferring data twice per cycle Rambus DRAM (RDRAM) – not the trend

9 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Error-detection using Parity Parity  Older method of error-detection  An additional parity bit to make an even/odd number of ones or an odd number of ones

10 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Error-correcting Code (ECC) Current method of error checking that can detect and correct an error of a single bit 8 ECC bits for 8 bytes (64 bits)

11 A+ Guide to Managing and Maintaining Your PC, Fifth Edition DRAM Speed Ratings Speed in nanoseconds – the minimum access time for a read/write to memory SDRAM  Speed in MHz – reciprocal of the nanoseconds speed E.g., 100 MHz (10ns)  Speed rating: PCXXX PC100-compatible (8ns)

12 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Packaging Dual Inline Packages (DIPs) Memory Modules A DIP A Memory Module

13 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Modules SIMM (Single Inline Memory Module)  30-pin: 8 bits of data (+ 1 bit parity)  72-pin: 32 bits of data (+ 4 bits parity/ECC) DIMM (Dual Inline Memory Module)  168-pin: 64 bits of data (+ 8 bits parity/ECC)  184-pin DDR: 64 bits of data (+ 8 bits ECC)  SODIMM – laptop computers RIMM: 184-pin

14 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Examples of Memory Modules

15 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 72-pin SIMM Intel 486, 586 and some early Pentium desktop 32 bits data width  36 bits with parity EDO and Fast page mode (FPM) technologies 4, 8, 16, and 32 MBytes 60ns – 70ns

16 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 168-pin DIMMs FPM, EDO, and Synchronous DRAM (SDRAM) 64 bits data width  72 bits (with 8 bits ECC)  80 bits (with 16 bits ECC) Buffered/unbuffered Serial Presence Detect: an EERPOM that stores configuration information of the module

17 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Identifying the DIMM Module

18 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Banks PCs read a certain bit width of memory at a time, typically 32 or 64, and the memory making up this width is called a bank 72-pin SIMMs: banks of two for a system with 64-bit system bus data path 168-pin DIMMs: installed as a single module for a system with 64-bit system bus data path

19 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Gold/Tin Connectors and Sockets 30-pin SIMMs: often with gold contacts 72-pin SIMMs: usually found with tin contacts 168-pin DIMMs: generally found only with gold contacts

20 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Size Specifications D*W-S  D: # of memory units for each bit  W: data width of the module in bits  S: speed of the module in nanoseconds E.g.  2x32-60  4x9-70  128MB16x64, 16x72

21 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Module Quality Factors DRAM Quality Number of Chips on the Module – beware of modules that have too many chips on them Module Quality Warranty

22 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Installing a SIMM Module

23 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Installing a DIMM Module

24 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Installing a RIMM Module

25 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Using Motherboard Documentation to Select Memory

26 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Using Motherboard Documentation to Select Memory ( continued )

27 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Troubleshooting Memory What to do if the computer does not recognize new SIMMs, DIMMs, or RIMMs, or memory error messages appear Recurring errors during normal operations can mean unreliable memory

28 A+ Guide to Managing and Maintaining Your PC, Fifth Edition DOS Memory Management

29 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Memory Layout Conventional Memory Upper Memory Area (UMA) 1 MB High Memory Area (HMA) 64 KB 384 KB 640 KB Extended Memory

30 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Conventional Memory The first 640 KB of system memory (00000h to 9FFFFh) Used by DOS and standard DOS programs (device drivers, user programs, etc……) Goal: free up as much as possible space to user programs

31 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Upper Memory Area (UMA) The next 384 KB of the system memory (A0000h - FFFFFh) Reserved for system BIOS, device BIOSes, and system devices

32 A+ Guide to Managing and Maintaining Your PC, Fifth Edition UMA Layout AddressFirst 16K (0000h-3FFFh) Second 16 K (4000h-7FFFh) Third 16K (8000h-BFFFh) Fourth 16K (C000h-FFFFh) A0000- AFFFFh Video Card RAM B0000- BFFFFh Video Card RAM C0000- CFFFFh Video Card BIOSIDE Hard Disk BIOS D0000- DFFFFh E0000- EFFFFh F0000- FFFFFh System BIOS ROM

33 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Upper Memory Blocks (UMBs) The parts of the upper memory that are not used by ROM or for video RAM EMM386.exe: a UMB provider that enables DOS programs and device drivers to access UMBs

34 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Load DOS programs in UMBs Config.sys must include device = himem.sys device = emm386.exe dos = UMB

35 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Load Device Drivers in UMBs Load device drivers in config.sys devicehigh = mydrive.sys  e.g, DBLSPACE.SYS, PRINTER.SYS, DISPLAY.SYS,RAMDRIVE.SYS Load DOS programs in autoexec.bat loadhigh program  e.g., DOSKEY, DOSSHELL, KEYB

36 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Extended Memory All of the memory above the first megabyte The first 64 KB (high memory area HMA) can be accessed by DOS programs Beyond 64 KB can only be accessed by Windows programs Himem.sys: manages extended memory

37 A+ Guide to Managing and Maintaining Your PC, Fifth Edition High memory Area (HMA) The first 64 KB after 1 MB of the memory (100000h-10FFEFh) HIMEM.SYS enables DOS programs (practically the DOS itself) to used this memory

38 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Load DOS High Open config.sys Type in device = himem.sys DOS = high

39 A+ Guide to Managing and Maintaining Your PC, Fifth Edition A Typical Config.sys device = himem.sys device = emm386.exe dos = high,UMB devicehigh = XXX.sys

40 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Windows Virtual Memory Management

41 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Virtual Memory Each application has 2 GB of virtual memory space 2 GB Virtual Memory Application 1 Application 2 2 GB Virtual Memory Windows VM Manager RAM Memory Swap File

42 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Virtual Memory Settings in Windows 9x Start->Settings->Control Panel->System- >Performance tab->Virtual Memory Change the size of the swap file Check c:\windows\win386.swp

43 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Virtual Memory Settings in Windows 2000/XP Figure 6-26 Open a MS-DOS window, type “dir /ah” to see the swap file