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Managing Memory

Managing Memory. RAM on the Motherboard. Loses all data when PC is turned off (except data stored on CMOS chip) Two categories Static RAM (SRAM) Fast Used as a memory cache Dynamic RAM (DRAM) Slower; requires constant refreshing. DRAM. SRAM. Memory Technologies.

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Managing Memory

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  1. Managing Memory

  2. RAM on the Motherboard • Loses all data when PC is turned off (except data stored on CMOS chip) • Two categories • Static RAM (SRAM) • Fast • Used as a memory cache • Dynamic RAM (DRAM) • Slower; requires constant refreshing

  3. DRAM

  4. SRAM

  5. Memory Technologies

  6. How SRAM Is Used in Different Memory Caches

  7. How Memory Caching Works

  8. Dynamic RAM Technologies • Stored on DIMM, RIMM, or SIMM modules (plug directly into motherboard) • Differences among these modules: • Width of data path that each type accommodates • The way data moves from system bus to module

  9. Examples of Memory Modules

  10. DRAM Technologies

  11. DRAM Technologies (continued)

  12. DRAM • SIMM technologies • Can use either EDO or FPM technology • DIMM technologies • Can use either BEDO (burst EDO) or synchronous RAM (SDRAM) • RIMM technologies • Each socket must be filled to maintain continuity

  13. Identifying the DIMM Module

  14. RIMM Technologies

  15. Error Checking and Parity • Parity • Error-checking procedure in which every byte has an even number of ones or an odd number of ones • Older method of testing integrity of bits • Stored in RAM or secondary medium • Sent over a communications device • Error-correcting code (ECC) • Current method of error checking that can detect and correct an error in a single bit

  16. Parity

  17. Other Memory Features • CAS (column access strobe) latency • RAS (row access strobe) latency • Both CAS and RAS refer to the number of clock cycles it takes to write or read a column or row of data

  18. Memory Speeds: Factors to Consider • Speed of memory in ns, MHz, or PC rating • How much memory is installed • Memory technology used • CL rating • ECC/parity or non-ECC/nonparity

  19. Factors That Contribute to Memory Speed

  20. Using Motherboard Documentation to Select Memory

  21. OS Memory Management • DOS and Windows 9x • Complicated; must deal with conventional, upper, and extended memory for backward compatibility • Windows NT/2000/NT • Eliminates complexity; memory is simply memory; all memory addresses are used the same way • Causes loss of backward compatibility

  22. Division of Memory Under DOS and Windows 9x

  23. How Memory Addresses Are Used

  24. How Memory Addresses Are Used (continued)

  25. Memory Management Evolution

  26. How Windows 9x and DOS Manage Memory Addressing

  27. Windows 9x and DOS Utilities That Manage Memory • Himem.sys • Device driver for all memory above 640K • Emm386.exe • Contains software that loads device drivers and other programs into upper memory

  28. How Windows 9x Manages Virtual Memory • Automates virtual memory management • Stores virtual memory in swap file and manages that memory for application programs • Controlled by the VMM (memory paging) • Symptoms of excessive memory paging • Very high CPU use • Very slow system response • Constant hard drive use

  29. Windows NT/2000/XP Memory Management

  30. How Windows 2000/XP Manages Virtual Memory • Default size of paging file is set to 1.5 times amount of RAM installed • Guidelines for managing paging files • Set initial and maximum size of file to same value • Balance file size with disk space usage • Move paging file to a volume other than boot volume • Remember that memory dumps cannot be captured if the paging file is on a different physical disk from the OS

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