🚀 go-pugleaf

Hello everybody. About one month ago, I mentioned my desire to add 64Kb
to my standard 640Kb on my AT. This is possible since I am using mono
and CGA video adapters only (No EGA, VGA, or MCGA). Unfortunately, no 
memory board was found at the time that filled the bill. There were 
a few problems:

  1) Memory boards usually can only add 128Kb at a time, not 64Kb.
  2) I want a 16-bit memory board, not a 8-bit PC type.
  3) The memory must be added at A000H (640Kb), which is unusual.
  4) The board must run at 13.8/9.3MHz.

Even though many people had tried to help, all attempts had failed and I
was giving up.

Well... This message brought up even more replies than the original one!
I must again thank heartily all those who made additional suggestions. I
recap as usual:

  A) You can use EEMS 3.2 or LIM 4.0 memory to do that sort of
     backfilling. There is a very nice utility on SIMTEL (and also
     available elsewhere) called EEMRAM Version 2.1 which does the
     trick. However, I already have 3Mb of EMS 3.2 only memory and I 
     don't want to buy an EEMS or LIM memory board just to backfill 64Kb!
     Of course, forget any kind of device driver emulators, we want
     true hardware.

  B) This suggests the following scheme. I use my 3Mb of extra RAM as
     exTENded. I could set aside 128Kb of that as exPANded EMS 3.2
     memory. Initialize the 64Kb cache at 640Kb. And then don't touch
     anymore that cache, leave it for DOS. That is, tell the BIOS about
     it and carefully reboot the machine without affecting the BIOS'
     data area and the 64Kb cache. I would then have 704Kb being used
     by DOS. DOS would never know its upper memory comes from an exPANded
     memory board cache. However, there is a catch in my case. My Everex
     board can only run in 8-bit mode since my CPU is too fast. I suspect
     every memory access to that 64Kb segment would have to be 8-bit wise.
     Of course, if DOS tries to use that 64Kb segment, it will do it
     in a 16-bit fashion. After all, the 80286 is a 16-bit CPU. I lose again.

  C) Tall Tree Systems makes PC and AT memory boards that can backfill
     at 640Kb the 64Kb of memory wanted. They are the JRAMIII AT and
     JRAMIII PC memory boards. Unfortunately, the AT-type board revision
     3 is designed for 8MHz and might be pushed to 10MHz. However, the
     salesman wouldn't recommend running it in my 13.8/9.3MHz AT-clone.
     None of the more recent Tall Tree boards have that feature either.
     There is no demand for it.

  D) It was also suggested that ATLAS Technology makes a similar memory
     board. It would appear it is 8-bit since they mention it running
     both in PC's and AT's. It then falls in the same category as the 
     Everex Mini-Magic.

I am now giving up this search, and for good. Pleeeaaase, do not try to help
me anymore! I made enough long distance phone calls. I also note that this 64Kb
of memory would be accessed through the bus, therefore relatively slowly.
I am not sure I like this. Perhaps DOS has a tendency to keep some frequently
used stacks up there. 

The moral seems to be, in these days of EGA and VGA, stick to 640Kb until
OS/2 or UNIX on 386's pick up speed and that 386's go down further more in
price. We may still have a DOS window that will let us run our old stuff
anyway.

Once again, I thank everybody.

                                            Francois
                                                '