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Expanded & Extended Memory

Posted on 2000-04-09
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Last Modified: 2012-05-04
I would like to know how it was used & how the momory was addressed.  I would really like the details of how this worked as much as possible.  Please help me. Thank you
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Question by:Citt
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by:fremsley
ID: 2699721
Under DOS all memory beyond 1MB is called 'Extended Memory' as the 80x86 CPU can not normally access it in real mode (with an exception for the first 64KB, also called 'high memory'). Usually it is accessed using a protected mode driver (XMS) by copying to and fro the lower conventional memory. 'Expanded Memory' (EMS) uses a different approach: there is a memory window (usually 64KB) in convetional addressing space below 1MB where pages from the extended memory can be mapped.

If you would like to learn more about how to program using XMS or EMS, I recommend Ralph Brown's Interrupt List:

  http://www.cs.cmu.edu/afs/cs.cmu.edu/user/ralf/pub/WWW/files.html

which contains information about almost anything concerning DOS and its drivers. However be warned: it's quite technical stuff.

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Accepted Solution

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coolcoder earned 200 total points
ID: 2742390
Thes is a list of the Memory Usage of Dos

Physik Adress            inlay
00000 hex      Interruptvektoren
00400 hex      BIOS - DATA            konventional
00500 hex      DOS - DATA            
00700 hex      DOS - Kernel            RAM
            Driver and Buffer
            COMMAND.COM (resident)
xxxxx hex      TPA-Transistent Programm Area  640 kb
A0000 hex      Video - RAM            reserved
C0000 hex      Video - Bios            area
C8000 hex      Free Workmemory                        
F0000 hex      BIOS                  384 kb
100000 hex      Extendet Memory
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Author Comment

by:Citt
ID: 2763830
THANK YOU!! I have no idea where you found this info, but it is great!! Thanks a lot!!
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