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1 MB of memory in XT?
- Thread starter Luke
- Start date
modem7
10k Member
PC/XT architecture
PC/XT architecture
The 8088 processor can address up to 1MB of memory (ROM/RAM).
However, the architecture of the PC/XT reserves the memory space between 640K and 1MB for things such as ROM and video RAM.
PC/XT architecture
The 8088 processor can address up to 1MB of memory (ROM/RAM).
However, the architecture of the PC/XT reserves the memory space between 640K and 1MB for things such as ROM and video RAM.
Last edited:
chuckcmagee
Veteran Member
Yes INDEED, I grew to hate that "upper memory area". I do not want to count the hours I wasted trying to get various drivers loaded up there. I don't miss "word perfect for DOS" one little bit 
I was always going to someone's PC, trying to get the print function to work. It always needed more memory than everything else so you would work for hours and hours trying to free up 10K of lower memory. Gah --- I want to forget those days.
I was always going to someone's PC, trying to get the print function to work. It always needed more memory than everything else so you would work for hours and hours trying to free up 10K of lower memory. Gah --- I want to forget those days.Terry Yager
Veteran Member
PC/XTs can use 'Expanded' memory (LIM), but you'll need to find the correct drivers for your board. Good luck.
--T
--T
Chris2005
Banned
Yes INDEED, I grew to hate that "upper memory area". I do not want to count the hours I wasted trying to get various drivers loaded up there. I don't miss "word perfect for DOS" one little bit
Every computer needs a certain amount of firmware. There has to be code present in non-volatile memory for boot up. I may need some edumucation on exactly what you're talking about, but drivers get loaded low in memory. And you aren't going to put anything "up there" if it's already occupied or if there's nothing there at all.
Chris2005
Banned
some computes, namely the DEC Rainbowm 100 and Tandy 2000 use more of it then a vanilla pc. I believe the Rainbow has ram all the way up to 896k. The Tandy had mods and aftermarket stuph that could pretty much go that high also.
Micom 2000
Veteran Member
I have a Phillips P3105 that has IIRC 720k usable memory. It's an XT. Haven't fired it up in some time tho.
Lawrence.
Lawrence.
The official memory map says 640K. If you have a CGA display you can get up to 736K by using the reserved memory between 640 and the start of the CGA video buffer.
In theory you could do the same thing if you had a monochrome adapter, but you'd get just 64K extra memory, not 96K. The monochrome display buffer starts a little lower.
The nice thing about these hacks is that if DOS is told about the extra memory, it can use it fairly normally. That's because it shows up as one big contiguous chunk. Anything not in a continuous chunk has to be treated in an unnatural way, like LIMS, the high memory area above 1MB on an AT, etc.
In theory you could do the same thing if you had a monochrome adapter, but you'd get just 64K extra memory, not 96K. The monochrome display buffer starts a little lower.
The nice thing about these hacks is that if DOS is told about the extra memory, it can use it fairly normally. That's because it shows up as one big contiguous chunk. Anything not in a continuous chunk has to be treated in an unnatural way, like LIMS, the high memory area above 1MB on an AT, etc.
Micom 2000
Veteran Member
I'm using an ATI video card with an old Nec 9pin connector. It won't read an AT keyboard, I'm using an
IBM XT one.
When it boots it displays:
ATI VGA Wonder+
Phillips PCRom 2.3
Testing memory -------------------------->
768k system memory
Then it goes to a menu program that I've left on it.
C:/
I then usually launch CMFiler (Charles Miller Filer- a great commander-like program)
Snooper reports;
CPU 8086-4.77
655,360 conventual memory
520,656 free
Dos 3.30
Extensions C000 C800
Environment Free 99 Total 160
No indication of XMS or EMS memory
Won't display anything in Bios.
IBMs Qconfig says pretty much the same except
CPU 8088
memory 640k
EGA 256k
Neither one mentions EMS memory. I figure that the available memory total is because of some assumptions by the programmers. I have yet to analyse it with Check-it or another program that Mueller recommends one of which will check each memory chip on your computer to find a bad chip. I'm fairly sure it must have 1 meg total but neither of those diagnostic programs mentions that. Can't remember if they usually do and report it as EMS memory. At some time I'll do that and see if it is an anomally with them.
Some time ago on classiccmp I mention this to some skepticism and a dutch member backed me up by stating that Phillips had indeed developed an overlay(?) which would overcome DOS' 640 barrier.
Lawrence
IBM XT one.
When it boots it displays:
ATI VGA Wonder+
Phillips PCRom 2.3
Testing memory -------------------------->
768k system memory
Then it goes to a menu program that I've left on it.
C:/
I then usually launch CMFiler (Charles Miller Filer- a great commander-like program)
Snooper reports;
CPU 8086-4.77
655,360 conventual memory
520,656 free
Dos 3.30
Extensions C000 C800
Environment Free 99 Total 160
No indication of XMS or EMS memory
Won't display anything in Bios.
IBMs Qconfig says pretty much the same except
CPU 8088
memory 640k
EGA 256k
Neither one mentions EMS memory. I figure that the available memory total is because of some assumptions by the programmers. I have yet to analyse it with Check-it or another program that Mueller recommends one of which will check each memory chip on your computer to find a bad chip. I'm fairly sure it must have 1 meg total but neither of those diagnostic programs mentions that. Can't remember if they usually do and report it as EMS memory. At some time I'll do that and see if it is an anomally with them.
Some time ago on classiccmp I mention this to some skepticism and a dutch member backed me up by stating that Phillips had indeed developed an overlay(?) which would overcome DOS' 640 barrier.
Lawrence
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Terry Yager
Veteran Member
If it's an 8-bit card, it probably can't be used as Extended Memory, It'll prob'ly be Expanded only. If there are switches/jumpers on board, ya might try a little experimenting.
--T
--T
chuckcmagee
Veteran Member
Hmmm, now that I think about it, all the computers I was talking about likely had at least 4 MB of memory to use. I would use "LH" (loadhigh) to load network programs, etc. This worked by "backfilling" upper memory with part of the 3 MB that was left. Soooo, yes, you need more physical memory to use the area between 640K and ! Meg.
CompositeGamer
Experienced Member
- Joined
- Feb 16, 2008
- Messages
- 53
i downloaded a program although not tested yet that uses ega or vga video memory as main memory below is some text from program docs
Are you tired of running short on memory? Well, you just found a
good solution.
ADDMEM.EXE is a memory resident utility (TSR) that temporarily
modifies certain aspects of your computer hardware and software to
simulate up to an additional 96K of memory. Poof! Suddenly, your
640K system will have up to 736K of RAM.
The memory that ADDMEM.EXE provides is NOT "extended" or
"expanded" memory. This is REAL memory that any program can
access. You don't have to do anything special to access it. Once
loaded, the program tells DOS that you have more memory. It's
that simple. Your programs will automatically recognize and use
the new memory just as if it had always been there.
Don't worry, this program doesn't do anything "dangerous" or
permanent. In fact, your EGA/VGA video card is specifically made
to do the things this program does. When you re-boot your
computer (or remove the TSR) you will have your old 640K system
back.
3. HARDWARE AND SOFTWARE REQUIREMENTS
=================================================================
o An IBM(R) PC/XT/AT/386/486 or true "compatible" running
MS-DOS(R) or PC-DOS(R) 3.0 or later.
o At least 640K System Memory (no less).
o EGA/VGA Video Adaptor with at least 128K Video RAM.
o One floppy disk drive or hard drive (of course).
o NOT compatible with Digital Research's EMM386.SYS.
Are you tired of running short on memory? Well, you just found a
good solution.
ADDMEM.EXE is a memory resident utility (TSR) that temporarily
modifies certain aspects of your computer hardware and software to
simulate up to an additional 96K of memory. Poof! Suddenly, your
640K system will have up to 736K of RAM.
The memory that ADDMEM.EXE provides is NOT "extended" or
"expanded" memory. This is REAL memory that any program can
access. You don't have to do anything special to access it. Once
loaded, the program tells DOS that you have more memory. It's
that simple. Your programs will automatically recognize and use
the new memory just as if it had always been there.
Don't worry, this program doesn't do anything "dangerous" or
permanent. In fact, your EGA/VGA video card is specifically made
to do the things this program does. When you re-boot your
computer (or remove the TSR) you will have your old 640K system
back.
3. HARDWARE AND SOFTWARE REQUIREMENTS
=================================================================
o An IBM(R) PC/XT/AT/386/486 or true "compatible" running
MS-DOS(R) or PC-DOS(R) 3.0 or later.
o At least 640K System Memory (no less).
o EGA/VGA Video Adaptor with at least 128K Video RAM.
o One floppy disk drive or hard drive (of course).
o NOT compatible with Digital Research's EMM386.SYS.
Anonymous Coward
Veteran Member
Programs like this that use the video adapter memory as conventional memory are interesting, but there are better ways of doing the same thing. Using the video adapter memory is said to be six times slower than the regular memory on your motherboard. There are programs such as LASTBYTE and QRAM that can do the same thing but instead use the memory on your expanded memory board or memory about 640k on the motherboard. Using these programs has no performance penalty.