8550 Controllers

rf5060a.exe 8550/Z Refdisk (not for the Reply OEM upgrades)

Still haven't figured out all the variants.
187-207 8550 MODEL R21
187-049 IBM PS/2 Model 50 (-021)
188-080 Model 50 Z  Systems with Improved Hardfile and Memory (-031,-061)

8550 ST-506 (50 pin edgecard)
8550 DBA-ESDI, Bare (72 pin edgecard, Bare card)
8550 DBA-ESDI 60MB (72 pin edgecard)

50z Riser ROMs Thanks to Dr Jim!
15F6994_U18.BIN U18 Even 15F6994
15F6995_U19.BIN U19 Odd 15F6995

8550 Drive Controllers (Peter Wendt)

60mbbuff.exe PS/2 60MB Fixed Disk Buffer Test v1.10
60mfdisk.com 60MB Fixed Disk Upg for M50-021 v1.00

Procom MC Pira IDE

Disk Drives

8550-021 - 20MB HD (uses 72X8505/90X8642)
8550-031,-061 - 160MB (used 90X9441, no chips) 50Z
8550-032 - 30MB 50Z
8550-061 - 60MB 50Z

My pocket ref says:

System FRU Size Interface IBM
8550 72X8522 20 ST506 WD325N
8550Z 6128287 30 ST506 "like" WD336RT
6128294 30 ESDI "like" WD387
8570 56F8895 160 ESDI "like" WD380S

8550 ST-506 FRU 90X8642

J1 50-pin edge connector
U1 Intel 8051AH microcontroller
U2 IBM 6127784
U3 IBM 6127893
U4 IBM 5960904
U5 Toshiba T5627
U7 83X3202
U10 Hitachi HM6116LFP-3
U25 Motorola MC3486P line recv.
U26 AMD AM26LS31PC line driver
Y1 12.0 MHz xtal (for U1)
Y2 20.017 MHz xtal (for U5)

Dave Beem spouts off with:
   Apparently it is a different drive (50-pin edge connector) than the 20 MB the Model 25/30 (44-pin) had. The Model 25/30 type also had a 30 MB brother that ran on the 286 version of those PS/2s. On the Model 50 the 20Mb was the only ST-506 drive type.


8550 Bare 90X9441  

David Beem says:
   90X9441 is ESDI. There are two circuit board variants of this, with no discernible differences: Circuit board 15F8434 has silkscreen outlines (not populated) for two capacitors & wider power runs than the 90X9354 circuit board.

90X9354 (90X9441)

8550 90X9571 P/N 15F6993 (50-021 w/60MB upgrade)

J1 72 pin edgecard socket
U18 BIOS 15F6994 (Even)
U19 BIOS 15F6995 (Odd)

U18, U19 D2764A-2 64K (8K x 8) UV Erasable PROM 180 ns [?] 28 pin

50z Riser ROMs

Dr Jim delivered the twins.
   I was able to remove the EPROMs with minimal damage but it was a PITA. Wouldn't use them in sockets, reliability might be an issue. I see good text in the code but of course I can't guarantee there isn't any random bit rot. Should be good though.

15F6994_U18.BIN U18 Even 15F6994
15F6995_U19.BIN U19 Odd 15F6995

Per Mueller:
   "In response to user complaints about the storage capacity of the original 20M Model 50, IBM offers the PS/2 60M hard disk drive as an upgrade option. You can install this drive by replacing the existing 20M [ST-506] hard disk in the PS/2 Model 50 (8550-021) or 30M [ESDI] in the Model 50 Z (8550-031).

   No trade-in is available for the earlier drive. This drive provides 60M of storage and a faster access time of 27 ms. The replacement adapter card required for the 50-021 is included [but is already there on the 50-031]."

8550 Drive Controllers
Peter H. Wendt     1/28/09

There are 3 risers from IBM:

- Bare ESDI riser for the Mod. 50Z to be used with the 72-pin card-edge drives. Passive. Does nothing but guiding signals.

- MFM controller for the 8550-021 with the "narrow" card-edge slot for the 20MB MFM drive. ID is DFFD, just like for the full length Mod. 60/80 MFM controller.

- ESDI upgrade riser, with the 72-pin card edge slot for the drive and some glue logic to make drive addressing possible, since the original Mod.50 lacks the ESDI code in the machine BIOS. Controller ID is also DF9F, which is that of the attached drive, which actually *is* a MCA controller card + drive mechanism in one. Back then ESDI was a big thing and AT only knew MFM (not even RLL). The early Mod. 50 BIOS is largely that of the AT ...

In addition I saw a 5.25" FDD controller riser (RFI ? Long gone), a variant of the ARCO IDE card (without rear bezel and handle), a similar thing from Procom for a 3.5" drive with a special sled (IDE most likely), a QIC tape adapter (Borsu or Iomega - can't recall), which feds a flat ribbon cable  out at the rear. Unit was a bulky 5.25" drive with power supply, fan and impressive power switch. And another tape adapter which operated with a floppy streamer in the second FDD bay. All these adapters were for the 50Z only, since that one did not need an extra HD controller - unlike the original -021 (non-Z).

Content created and/or collected by:
Louis Ohland, Peter Wendt, William Walsh, David Beem, Tatsuo Sunagawa, Jim Shorney, Tim Clarke, Kevin Bowling, Tomáš Slavotínek, and many others.

Ardent Tool of Capitalism - MAD Edition! is maintained by Tomáš Slavotínek.
Last update: 23 Jan 2022 - Changes & Credits | Legal Info & Contact