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Conventional Memory

Conventional Memory. 8088 processor could address only 1 MB original DOS memory had two sections: Base Memory occupies first 640KB of addresses originally reserved for use by DOS and its programs Upper Memory Area (UMA) occupies remaining 384KB

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Conventional Memory

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  1. Conventional Memory • 8088 processor could address only 1 MB • original DOS memory had two sections: • Base Memory • occupies first 640KB of addresses • originally reserved for use by DOS and its programs • Upper Memory Area (UMA) • occupies remaining 384KB • reserved for BIOS and peripherals (e.g., video card, hard drive controller, etc.).

  2. Shadow RAM • Shadow RAM: a memory-usage scheme that improves overall system performance • With this feature, the contents of the ROM BIOS and/or Video BIOS are rewritten (shadowed) into the Upper Memory Area. • This enables system to operate faster when application software makes use of BIOS routines.

  3. Extended Memory • Extended memory: Memory addresses beyond the original 1 MB limit of the 8088 • But DOS can’t access beyond 640K

  4. Memory managers • Later processors were able to access more RAM beyond the original 8088 • 286 processor could access up to 16MB • 386 and 486 could access up to 4 GB • Memory managers are special add-on programs that enable DOS to access and use the additional memory available to more powerful microprocessors. • Added to CONFIG.SYS

  5. Device=C:\DOS\HIMEM.SYS Device=C:\DOS\EMM386.EXE FILES=30 BUFFERS=15 STACKS=64,500 DEVICE=C:\DOS\SMARTDRV.SYS 1024 DOS=HIGH, UMB DEVICEHIGH=C:\MOUSE\MOUSE.SYS DEVICEHIGH=C:\DOS\RAMDRIVE.SYS 4096/a Roles of CONFIG.SYS sets up memory managers configures DOS for use with options, devices and application programs loads device drivers

  6. HIMEM.SYS • memory management program that manages extended memory above 1024KB • add line to CONFIG.SYS • HIMEM.SYS shifts most of the operating system functions into the High Memory Area (HMA) of extended memory. • The HMA takes up the first 64KB of addresses above the 1MB boundary • HIMEM.SYS must be running for Windows 3.x to run

  7. EMM386.EXE Frees up conventional memory by allowing unused portions of reserved memory area to be used for DOS drivers and memory-resident programs • Add line to CONFIG.SYS: Device=C:\DOS\EMM386.EXE DOS=UMB

  8. FILES=30 BUFFERS=15 STACKS=64,500 FILES command establishes the number of files that DOS can handle at any one time to 30 (minimum number required to load Windows for operation.) BUFFERS sets aside 15 blocks of RAM space for storing data being transferred to and from disks. STACKS establishes the number and length of some special RAM memory storage operations at 64 memory stacks, with each being 500 bytes long. More on CONFIG.SYS

  9. High Memory • The first 64K of the extended memory area • Only part of extended that a real mode program can access • In Config.sys type the DOS=HIGH command • With this statement DOS will load most of its cod to HMA instead of conventional • This frees up more conventional

  10. LOADHIGH and DEVICE HIGH • LOADHIGH used on the DOS command line or in AUTOEXEC.BAT to start a program and place it into upper memory. • DEVICEHIGH used in the CONFIG.SYS file to assign a device driver to UMB

  11. MEM and Memmaker • MEM command reports status and usage of all memory. Run it with the /C option to see how memory is being utilized. C is short for “classified”. • MemMaker-, available in DOS 6.0 or later, manages UMB and extended memory. Used to automaticly optimize memory usage.

  12. Memory Management in Win 3.x • Win 3x needs HIMEM.SYS to load. • Uses temporary swap file WIN386.SWP • Uses permanent swap file 386SPART.PAR • 3 core file to manage memory • KRNL386.exe-loads and executes windows programs • GDI.EXE- handles graphic displays • USER.EXE- handles user input, display icons, windows and dialog boxes

  13. Memory Management in Win 95 • Eliminated need for DEVICE entries in the CONFIG.SYS file with the advent of a group of 32 bit protected mode device drivers. These drivers are automatically loaded into extended memory when it loads. Are referred to as virtual device drivers and have the a .VXD or .386 extension

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