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From: v087mxgb@ubvmsa.cc.buffalo.edu (Shawn E Thompson)
Newsgroups: comp.sys.misc
Subject: Re: IBM PC-XT RAM Chips?
Message-ID: <43765@eerie.acsu.Buffalo.EDU>
Date: 1 Nov 90 13:54:55 GMT
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>is twofold:  can this board be populated with 640k using 256x1 and 64x1
>chips, and if so, what are the proper dipswitch settings?
>|  Washington University  |   everyday, J. R.,   |   Me worry?     |
Quoting from IBM's 'Technical Reference Manual: Personal Computer XT and
Portable Personal Computer' (IBM manual #6322508);

" RAM

The system board also has from 128K by 9 to 256K by 9 of R/W memory. A 
minimum system would have 128K of memeory, with module sockets for an 
additional 128K. Memory greater than the system board's maximum of 256K
is obtained by adding memory cards in the expansion slots. The memory 
consists of dynamic 64K by 1 chips with an access time of 200-ns and a cycle
time of 345-ns. All R/W memory is parity checked."

This manual refers the user to the 'Guide to Operations: Personal Computer XT"
for dipswitch settings, which consists of FIFTEEN pages of switch settings
(the eight switch block on the system board is as follows:

   switch #1 ALWAYS OFF!!
   switch #2 math coprocessor (yes or no)
   switch #3 & #4 on board RAM (off-on=128K,on-off=192K,off-off=256K) 
                  system board must be fully populated before you can add 
                  a memory expansion option.
   switch #5 & #6 graphics adaptor (off-on=CGA in 40x25 mode, on-off=CGA in 
                  80x25 mode, off-off=monochrome, on-on=no display)
   switch #7 & #8 drives (on-on = 1 floppy, off-on=2 floppies)


The remainder of RAM options are set with switch blocks on the RAM
expansion cards (TWELVE pages of settings).

I use an Inboard and/or above board (depending on which system), and
have 1280K addressable RAM - works very well.





Shawn E. Thompson "..my sig file was so long, I'm not even allowed a quote..."
v087mxgb@ubvms.cc.buffalo.edu | set@autarch.acsu.buffalo.edu
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