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UMB on an 8088 without a V-20

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k2x4b524[

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Greetings, i am revisiting something i was trying to do before, and that is getting umb on a plain jane xt, qram is good to go and so is my ems board. None of the usual driver files work, so that means dos-up is out of the question till i get at least a v20. Anonymous Coward, i saw you were running a v-30 in one of your rigs, is the v30 pin compatible with the 8088?
 
It's all about the GAL in u44. It defines which blocks of memory are addressable. So, even though 384K additional RAM is present on the motherboard, only D000 thru EFFF are listed as addressable by the custom GAL in u44. Therefore, no conflicts with adapter roms or bios rom exists since they normally don't reside in this area.

I'm the one who convinced Chuck(G) to help with the programming of the GAL. Then I bought his programmer. So, if you're interested, I'd be happy to supply a programmed GAL if you want to do this mod. I'd also be glad to assist with setting up the drivers that I used to set up UMB's on my 5155(Use!umbs.sys, Clearmem.sys by Chuck, Dosmax.exe). I have a V-20 in my machine, so i'm not sure if the drivers that I use would work on a 8088. But, the V-20 is a cheap and worth while upgrade for any XT.

edit; I originally typed u84, it should have been u44
 
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The custom decoder logic I think is needed only if the extra physical capacity is coming from chips in the on-board slots (?). Adding the RAM on an ISA card OTOH it can be slotted in anywhere there is space.

The Tandy 1400 laptop I think uses that kind of approach, providing 128KB at DC000h (to FBFFFh). So the ROM in that machine has just 16KB.
 
pearce_jj said:
The custom decoder logic I think is needed only if the extra physical capacity is coming from chips in the on-board slots (?). Adding the RAM on an ISA card OTOH it can be slotted in anywhere there is space.
Click to expand...
The ISA card would handle the addressing logic. The u44 logic is somewhat limited in that it can only address memory in 64K blocks. So, if you have a 16K or 32K hole some where in the upper range, it cannot be addressed with the GAL in u44. I would think that some ISA memory cards would have a more flexible addressing scheme. However, doesn't expanded memory use part of the D000h - EFFFh area for the page frame? That would reduce the amount of memory available for UMB.
 
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Yes indeed, EMS is accessed through a page window that will be located in the UMA. I just read something interesting on Wikipedia, "Support for the A20 gate was removed in the Nehalem microarchitecture" - does that mean that Himem can't run on such?
 
pearce_jj said:
Yes indeed, EMS is accessed through a page window that will be located in the UMA. I just read something interesting on Wikipedia, "Support for the A20 gate was removed in the Nehalem microarchitecture" - does that mean that Himem can't run on such?
Click to expand...

Not at all--the A20 gate was a kludge on IBM 80286 systems (and clones) that would force a wrap to 00000 if the next location past FFFFF was addressed (to emulate the 20 line address in the 8088/86).

It was intended to make a very small number of DOS programs happy--I can't even remember what they were.

It was a silly kludge anyway.
 
k2x4b524[;
I sent you a pm with the correct socket number, u44 instead of u84 since the other day I was typing the wrong one including the original PM that I sent to you. I guess I'll need to be more carefull to double check before posting.

Greg
 
Wait... what is this???

I have an old KayPro 8088 that my parents bought when I was a kid. I've got it in storage, but I'd love to get it out and mess around with it.

It's got 768k of memory, but I've never really been able to use the extra 128k. It had 640k base that we used... but I vaguely remember using the 128k as a RAM-DRIVE loading some kind of RAMDRIVE.SYS in memory that would then copy the command.com to it and set the COMSPEC.

Is there some way I can do DOS=UMB or something and actually have it do something???


Todd
 
Correction: backward compatible! V20 and V30 have extra instructions. In fact, the V20/V30 instruction set is more like the 80186 (plus an extra 8080 emulation mode).
 
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