Memory in Dos

[andtp]

I bought More memory for my computer and now I only have 640kb in dos when I should have 66mb.

[Igor M]

Hi,

MS-DOS uses the memory not as one continuous piece but divides it into several types. The memory you said about is conventional memory. Its never be over 640K because 640K is its upper limit. To run DOS based programs you can use only this 640K of conventional memory. Part of memory between 640K and 1M can by converted into Upper Memory Blocks (UMB) and can be used for loading device drivers. Memory above 1M can be used by DOS programs for data storage only (unless the program uses DOS4GW extender) and can be represented as XMS (extended) or EMS (expanded) memory. Besides you can use 64K segment just above 1M as High Memory Area (HMA) and load into it your system files. You can run MEM from DOS prompt and look what the total amount of memory you have and how it is divided on the different types. (Keep in mind, to use other types of memory in DOS you must install HIMEM.SYS and EMM386.EXE memory drivers. Without them you will have conventional memory only despite of total amount of RAM installed.)

Good luck, Igor M

[ggre123]

Also, you might want to add the /EISA switch in your Himem.sys line in Config.sys:

C:\DOS\HIMEM.SYS /EISA

In some (or all - I'm not sure) versions of DOS, it has a limitation of only seeing a maximum 16MB of memory. The /EISA switch tells DOS to look above 16MB for additional RAM.

[ggre123]

Also, you might want to add the /EISA switch in your Himem.sys line in Config.sys:

C:\DOS\HIMEM.SYS /EISA

In some (or all - I'm not sure) versions of DOS, it has a limitation of only seeing a maximum 16MB of memory. The /EISA switch tells DOS to look above 16MB for additional RAM.