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.).

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.

Extended Memory

Extended memory: Memory addresses beyond the original 1 MB limit of the 8088

But DOS can’t access beyond 640K

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

Roles of CONFIG.SYS

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

sets up memory managers

configures DOS for use with options, devices and application programs

loads device drivers

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

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

More on CONFIG.SYSFILES=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.

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

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

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.

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

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