Japanese SCSI /A

Information about the SCSI/A adapters used in the PS/2 line can be found HERE.

Short SCSI /A (A/16) (DIP Terminator)
Short SCSI A/16 (SIP Terminators)
2/3 Length SCSI/A (50-pin Header + Card Edge)
Short SCSI A/32 with Cache (DIP Terminator)
Short SCSI A/32 with Cache (SIP Terminators)
2/3 Length SCSI/A with Cache (50-pin Header)
Long SCSI A/32 with Cache and 2.5" HD
SCSI Investigation

Content created by Sandy. Edited and new outlines created by Major Tom.

Short SCSI /A (A/16) (DIP Terminator)

(P/N 35G2976) [P] [P] [P] (P/N 66G1080, FCCID: ANOTPS) [P] [P] [P]

J1 Internal SCSI Header
J2 C60 External SCSI Port
J3 Artifact
U2 SCSI BIOS Odd 92F2245
U3 33F6715
U4 33F6910
U5 SCSI microcode 54G1800
U7 SCSI BIOS Even 92F2244
U8 Intel 80C32GBAA
U9 84F8324 Line Interface
U15 CXK5864BM-10LL 8Kx8
RN1 Resistor pack (term.)
RT1 polyfuse
Y1 20 MHz xtal
Y2 25 MHz xtal

U8 Intel 80C32GB - 10MHz microcontroller as busmaster CPU
RN1 Resistor pack (term.) - Bourns 4120R-003 221/331 - Dual Terminator 220 Ω / 330 Ω
RT1 polyfuse - Littelfuse 100 HG9K

J3 Serial Interface - status link header like on the late SCSI w/cache. From left to right, the pinout is CHR, ITS, BRN, TXD, RXD, GND

Short SCSI A/16 (SIP Terminators) (P/N 07G3169) [P]

Short version of uncached SCSI /A with AIC6250EL and old SCSI microcode set.
Long uncached SCSI /A was equipped in PS/55 5570 (analogous to 8580 25 MHz).
I think this short card was an option for 5530-U/V but I'm not sure.

U1 HM6264LFP
U2 SCSI BIOS Even 64F4376 (27C256)
U3 SCSI BIOS Odd 64F4377 (27C256)
U4 SCSI microcode 84F8233 (27C256)
U6 N8032AH
U7 OKI 15F7917
U9 33F6715
U10 OKI 33F6910
U11 Adaptec AIC-6250EL
Y1 "125KD"? xtal
Y2 "20AKSS1M"? xtal
RN1-3 Terminator Resistor Packs

2/3 Length SCSI/A (50-pin Header) (P/N 79F1140) [P]

Not sure about this one. Maybe uncached SCSI for 5560-W0. Got this one recently (2003.05.11). This one has 2 internal connectors, one is 50-pin flat ribbon cable connector and the other is 50-pin edge card connector.

U1 SCSI microcode 84F8233
U2 SCSI BIOS Even 64F4376
U3 SCSI BIOS Odd 64F4377
U10 33F6910 M91V034 OKI
U12 33F6715
U20 HM6264ALFP-15R
U21 N8032AH
U24 Adaptec AIC-6250EL
U25 15F7914 M91H048 OKI
F1 Fuse
Y1 20.000 MHz xtal
Y2 Unknown xtal
RN1-3 SIP Terminators
J1 50-pin SCSI Connector
J2 50-pin Edgecard connector
J3 Extrnal RS6000 style connector

Short SCSI A/32 with Cache (DIP Terminator) (P/N 35G2818) [P] [P] [P]

This is the Latest SCSI 32/A, probably an option for 5551-Rxx. Basically this adapter is capable to handle drive >1G. Unfortunately most of PS/55s (except 9595 and 8595-J) can't handle IML drive larger than 1G with this adapter due to BIOS issue. 8595-Jxx (1S1P planar with Type 3 50 MHz complex) with this adapter can handle HD over 1 GB as IML drive. SCSI ID for IML drive is not restricted to #6 for this combination.

U1 84F8324
U2,7 9336HAK, TC514256AJL-70
U3,8 9336HAK, TC514256AJL-70
U4,9 9336HAK, TC514256AJL-70
U5 SCSI BIOS Odd 92F2245
U6 SCSI BIOS Even 92F2244
U10 15F6903
U11 33F6715
U12 SCSI microcode 10G4890
U13 Intel N80C188XL 20
U14 M5M5256BFP-12L
F1 Fuse
Y1 20.000 MHz osc
Y2 32.000 MHz osc
Y3 25.000 MHz osc
RN1 Yellow DIP Terminator

I once fried the F1 fuse when I attached a Rancho's Single/Differential converter. Really got shocked because that was the only one "> 1 GB capable card" I had back then. I trolled around parts shops in Akihabara and got a similar type of tiny chip named "Poly switch". Electrical specification was a bit different but with the chip my card revived.

Short SCSI A/32 with Cache (SIP Terminators) (P/N 07G3063) [P] [P] [P]

U1 84F8324
U2,7 9306HAK (T51256T-70)
U3,8 HM512456AJP8 (cache)
U4,9 HM512456AJP8 (cache)
U5 SCSI BIOS Odd 92F2247
U6 SCSI BIOS Even 92F2246
U10 15F6903
U11 33F6715
U12 SCSI microcode 10G4891
U13 Intel N80C188-16
U14 M5M5256BFP-12L
F1 Fuse
Y1 20.000 MHz osc
Y2 32.000 MHz osc
Y3 25.000 MHz osc
RN1-3 Register Packs (removable)
RN4 Register (soldered)

2/3 Length SCSI/A with Cache (50-pin Header) (P/N 95F4488) [P] [P] [P] [P] [P]

This adapter is an earlier version of SCSI 32/A and was equipped in 5561-W1x/W2x models. SCSI microcode set is 64F4356/57 and it can't handle drive > 1 GB as ID6.
Probably this is the only one with usual 50-pin flat ribbon inner connector among all of IBM's genuine SCSI /A for PS/2 and PS/55. But there is another one, see below for P/N 79F1140.

U1 Adaptec AIC-6250EL
U2,7 M5M4256AL-10 (ZIP RAM)
U3,8 M5M44256BL (cache, ZIP RAM)
U4,9 M5M44256BL (cache, ZIP RAM)
U5 HM62256LHP-15T
U10 SCSI microcode 64F5984
U11 Intel N80C188
U12 15F6903
U13 33F6715
U15 SCSI BIOS Even 64F4376
U18 OKI 15F7917
U19 SCSI BIOS Odd 64F4377
F1 Fuse
Y1 20.000 MHz osc
RN1-3 Resistor pack
RN4-6 Resistor packs (term.)
RN7 Resistor pack
J1 DB50 SCSI Header

Long SCSI 32/A with Cache and 2.5" HD (P/N 35G3785) [P]

2.5" SCSI HD is mounted on the adapter. The drive is set to ID #6. The stock HD is WDS280 (80 MB).

U1,2 HM514256AJP8
U3,6-8 HM514256AJP8
U4 84F8324
U5 15F6903
U9 SCSI microcode 10G4890
U10 33F6715
U11 Intel N80C188-16
U12 SCSI BIOS Even 92F2244
U13 SCSI BIOS Odd 92F2245
Y1 20.000 MHz osc
Y2 25.000 MHz osc
Y3 32.000 MHz osc

All chips on the PCB are same with short SCSI 32/A with cache P/N 35G2818 with Yellow DIP Terminator. Just the parts are reallocated on the PCB.

SCSI Investigation

I'm not sure if I'm correct or totally wrong about the following info. I tested and experienced by myself thus I wrote. I can't explain my experience logically 'cause I can't read BIOS or don't have sufficient documentation about PS/55's SCSI feature.

It is told that PS/55's BIOS lacks, unfortunately, support for over 1 GB IML drive. Even if we use 92F2244/92F2245 SCSI BIOS and 10G4890 microcode, PS/55s such as 5580, 5560 and 5551-N can not accept IML drive larger than 1G capacity. Server models like 9595 (Type 4), 8595 (Type 3) and 9585 are capable to run drives > 1 GB as IML and they are basically same with pure PS/2. In another word, BIOS ROM in Japanese localized processor complexes (and planar) are not sufficient to take drives > 1 GB as it's IML drive even though we use SCSI adapters with enhanced SCSI code. We have such nice cards over here but it's true. It's ridiculous and sad.

Group A Adaptersnot capable to handle > 1 GB IML and/or boot drive

P/N Bus Size Equipped BIOS P/N ROM Type Trm. Cache
6451018 32-bit Long 5580-Y 64F4376/77 EPROM None Yes
15F6561 16-bit Long 5570-V 64F4376/77 EPROM DIP No
95F4480 32-bit 2/3 5560-W1 64F4376/77 Flat package SIP Yes
07G3169 16-bit Short 5551-W ? 64F4376/77 Flat package SIP No

Group B Adapterscapable to handle > 1 GB IML and/or boot drive

P/N Bus Size Equipped BIOS P/N ROM Type Trm. Cache
35G2976 * 16-bit Short 92F2244/45 Flat package DIP No
66G1080 *? 16-bit Short 92F2244/45 Flat package DIP No
35G2818 32-bit Short 5551-R ? 92F2244/45 Flat package DIP Yes
07G3063 32-bit Short Option 92F2246/47 Flat package SIP Yes
6451280 32-bit Short Server 61G3929/30 Flash ROM Yes
92G1572 32-bit Long 8595-Jxx 92F2244/45 EPROM DIP Yes

* Not capable to handle partition > 1 GB as a boot drive. Ed. Huh? But the title says "capable".

Flat package. Don't know correct term for the ROM. It's a flat, SOJ type ROM (write-one-time).


5580-Y with Type A Upgrade complexes (DX2-66), HD; Seagate ST42400N. Can't make system partition on the Seagate even with an adapter listed under Group B. The Seagate drive IDed as 6 off from 35G2818 can't be recognized as valid drive for IML.

If I use a smaller drive with ID=6 and make system partition on it, then change boot order to Seagate 2G in one partition as C, then system works. Here, if I change SCSI /A to listed under Group A, system stops upon booting with error message "Missing Operating System". If I change older type of SCSI /A to newer one again such as 35G2818 or 07G3063, every thing works fine.

If I change Type A Upgrade to Type 3, the Seagate drive off from 35G2818 and 6451280 (both in Group B) works fine as like as usual PS/2 with Type 3 platform. Also I can give SCSI ID other than 6 to ST42400N.

Conclusion (If I'm correct):

  1. Pure PS/55s dose not contain SCSI code in it's BIOS or lacks some important codes relating SCSI. Server models (5580 and 5560) may handle drives larger than 1 GB if BIOS ROM could be replaced. IBM Japan had not ever released such BIOS ROMs nor reference versions. I'm not a BIOS tweaker.
  2. SCSI adapters listed in group A can not handle drive larger than 1 GB for IML purpose. Also it can't boot OS even IML drive is smaller than 1 GB and boot order is changed to another drive larger than 1 GB in which OS is installed.
  3. SCSI Adapters listed in group B can handle drive larger than 1 GB for IML purpose only when it is used with PS/2 complexes including PS/55 Type 3. In this case SCSI ID for IML drive is not limited to ID 6. With Japanese Type 1/2 and dx2-66 upgrades, SCSI adapters in group B on 5580/5560 can't do it.
  4. As a matter of fact, 5551-N can not handle drives larger than 1 GB as an IML drive even though it has 92F2246/2247 microcode set on the planar.

Why Big Blue Japan deleted SCSI code from machine BIOS?

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