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Chapter 6

Chapter 6. Managing Memory. 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. EEPROM.

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Chapter 6

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  1. Chapter 6 Managing Memory

  2. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  4. RAM A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  5. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  6. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  7. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  8. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  9. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  10. 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) A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  11. 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) A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  13. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  15. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  16. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  18. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  19. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  20. 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 • 128MB 16x64, 16x72 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  21. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

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

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

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

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

  27. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

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

  30. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  32. UMA Layout A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  33. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

  35. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  36. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

  37. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

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

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

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

  42. 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 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

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

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