🚀 go-pugleaf

In article <5038bdcd.20b6d> angelini@apollo.HP.COM (Bob Angelini) writes:
>|> I'm looking for someone with information about the original 6 MHz AT
>|> Memory.  Now on the XT's, there was a way to upgrade the board to 640..

   Sorry, this is true only of the 256-640 system board. This would have been
the last production run, and only accounted for a very small (1%) of the ibm
xt population.  I have only seen one of these out the several hundred ibm's
I've cracked open.

>|> looking for someone with info on the same thing for the 512k AT motherb
>|> This is the full-sized baby...

>The original AT's use piggy-backed 128Kbit drams modules 
>(for 256K bit/module). These chips are not pin compatable with standard 256K 
>bit drams. The easyist way to upgrade either a 256K or 512K AT is with any
>... 3rd party memmory boards. 

1. Did IBM ever make a 'baby AT', I've only seen 'the full-sized baby'.
2. Did IBM ever make a 256K AT motherboard, I've only seen 512K motherboards
   of which 256K probably could have been a standard config.
3. The motherboard has 4 banks of sockets, so if they were piggy-backed 128K
   chips for 256K bit/module, this would be 1 MB on the motherboard  (yes
   the 286 is 16 bit, but there are 2 extra parity chips then, or the 
    measurement is still 8 bit words, or the documentation itself calls it
    512, logically then, theses are piggy backed 64K drams forming 128K
    drams.  It is possible to reverse 'engineer' these 128K drams from 64K
   drams by jumping pins, but the resulting kludge is too big to fit under
   many cards.
4. IBM made a 512K to 640K memory expansion card I have seen several adds for
   available today, used.  It used the same chips, and the chips are also
    available used today.  The cost of either of these makes it more cost
   effective to use a 3rd party board.
5. MANY 3rd party boards do NOT allow addressing back into the 512k to 640K
   region.  The feature is called back filling or split (range) addressing
   generally.  I'd say that MOST 'NAME BRAND' (intel/inboard/inboard plus,
   or ast for example) will provide this feature.  However, thie will result
   in a amount of extended/expanded memory that is a 'odd' amount.
Given the cost of addin boards, and the resulting performance gains from
512 to 640K, I believe that you may be better off letting the addin board
provide more extended/expanded memory and NOT ffilling the 512 to 640 region.
That is of course, if you don;t have a application that requires more base
memory...
al
-- 
Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University
 InterNet: amichiel@rodan.acs.syr.edu  amichiel@sunrise.acs.syr.edu
 Bitnet: AMICHIEL@SUNRISE