PS/2 8550/8560 reference diskette v1.08
PS/2 MODEL 50 (8550-021) 20MB/1.44MB/1MB
8550 -R21 Identical to -021 except it has a 50-key function keyboard intended
for use primarily in the teller workstations of
financial institutions. This keyboard is commonly used for basic
teller applications which usually deal with limited, mostly numeric, input
and output. It is not intended for use with general purpose applications.
The 50-021 / -031 lacks the ESDI part of the BIOS.
Peter Wendt scrawled:
If you pick the 50Z BIOS chips (2 x 512) and split-burn
them down into 4 x 256 (as the 50-0xx uses them) you can convert a 50-0xx
into an "almost 50Z" without needing the "50-to-50Z upgrade controller",
which is a rare item. It only adds the ESDI code to the BIOS and needs
a different @DF9F.ADF, which allowes to set an adress for the BIOS ROM
on the controller.
Did that a decade ago and it seemed to work fine with
a 50-021 and a 120MB HD from a Mod. 70.
>Couldn't you also replace bits of the BIOS in software? Get the
BIOS copied into RAM as is sometimes done for performance, then overwrite
bits of it. I dunno if anyone has actually done this, but it sounds
The 286s don't copy the ROM into RAM after POST like the
386s do - and even if: you should do that *before* POST to have the ESDI
controller available for the boot process .... but I don't think that was
what you *meant*.
[Rem: The "upgrade controller" in fact *does* something
similar: it copies some routines into an appropriate area in the "adapter
ROM area" (C000 - DFFF) and sets the bootloader entry point to the start
of that routine. Usual "check adapter segments for bootable controller
Using "Split Copy" on an Eprommer is much better. You
pick the "even" of the two 27C512 (64K x 8 bit) Eproms, read and store
0000-7FFF in the first and 8000-FFFF in the second process.
Then you pick the "odd" Eprom and repeat the step. The
four files nicely burn into 4 x 27C256 (32K x 8 bit) Eproms and you have
Odd-Low, Odd-High, Even-Low, Even-High.
It's *a little* complicated - but not much. (Even I managed
...) ;-) I think I still have the codes in my data cemetry somewhere.
In the 50-021-format.
The advanced Do-It-Yourselfers *may* pass this obstacle with this method:
- copy the 50Z-BIOS from 2 x 27C512 into 4 x 27C256 (split the "ODD"
and "EVEN" eprom into ODD-Low and ODD-high, EVEN-low and EVEN-high. 0000h
- 3FFFh = low, 4000h - 7FFFh = high at each set) This requires an Eprommer
- install the new BIOS chipset on the 50-021 planar
- use the bare "Hardfile Riser card" 90X9441 from the 50Z
- use any of the IBM ESDI drives (30-160MB)
- reconfigure the machine. "1 ESDI harddisks" must be displayed in
device-list on advanced diagnostic (unmodified 50-021 show 0 ESDI drives
here on that attempt ...)
The 50-021 uses a proprietary MFM / ST-506 controller along with a CMOS
version of a MFM 20MB harddisk - and that's the only drive supported on
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