SCSI Drives Over 1 GB

Maximum Drive Size on Type 4
IBM SCSI w/Cache - Swapping BIOS chips for >1 GB Support

What sort of problems can show up?
Which machines can't be reworked to take larger drives?
Which systems do not exhibit the problem or can be reworked?
Fixing the problem in the Machine BIOS
Fixing the problem in the SCSI Adapter BIOS
Complex BIOS Upgrade Needed for >1GB IML Drive
System partition size on on a >1GB drives
Using other IBM or Non-IBM SCSI controllers

Version 1.0b - revised by Tim N. Clarke, reformatted by Tomáš Slavotínek

This page contains some hints and tips for those who feel the need to stuff a more modern harddisk in their machines - preferably one larger than 1GB. However this includes some possible pitfalls. To check out what to do and what to consider before buying the latest and fastest multi-GB drive - read on.

The Problem: I want to install a SCSI drive over 1GB, and I'm not sure if it can be done.

The Solution: Read the following on how to make your system "over 1GB capable".

It is a good idea to fit a much more modern and mechanically faster harddisk in a PS/2 instead of the old, slow and mostly small original drives and a good tuning measure too.
This is especially true for machines running OS/2, Win95 or WinNT which "hit the swap-file a lot". These will become much more responsive with a modern drive.
The IBM DCAS-32160, the Quantum Fireball TM-2110S and the Quantum Fireball SE/ST with 2.1 and 3.2GB have been proven to be good choices. They're Ultra-SCSI (SCSI-3) drives - but the IBM SCSI adapter can handle them due to the downwards compatibility of the SCSI standard. Of course it will not be able to handle them at Ultra-SCSI speed of 20MB/s. The average access-time on these drives is 8.5-10 ms - which is darn fast compared to the 16 ms or more of the old drives used in most PS/2 machines. This may not sound overwhelming, but remember that the new drives store x-times more bytes per track than the old ones and change track in half the time...

This adds up to a significant performance boost in the end.

I, naturally, prefer the IBM... for obvious reasons.

What sort of problems can show up?

Various IBM PS/2 systems - especially the older 85xx types - are known to be pretty tricky when it comes to installing a SCSI harddisk with a capacity over 1GB.

This can be due to one or more of a number of reasons:

  • the system has an old harddisk adapter without enhanced translation
  • the system BIOS does not support drives over 1GB at all
  • the drive is the primary or only drive
  • the system uses a system partition (IML machines)

In most cases a larger drive will be accepted as an additional drive with fewer problems. Just use a SCSI address other than those used by devices already present and run a Low-Level format on this new drive with the advanced diagnostics. In most cases that will do it unless, perhaps, it is a large drive of over 8GB - which cannot be handled by the earlier BIOS and operating system.

Which machines can't be reworked to take larger drives?

Basically there are only a few machines that cannot handle SCSI drives over 1GB and retain the original specification:

  • IBM PS/2 8573-161 and -401 Portable P75 (1)
  • IBM PS/2 8556 56SX and 8557 57SX (2)(3)
  • IBM PS/2 9585 -xXx Server 85 (4)

1) Non-IML, onboard SCSI, old BIOS, no fix available
2) Non-IML, onboard SCSI, old BIOS, no fix available.
System supports a "service partition" for convenience.
3) Later systems *may* be able to handle drives over 1GB (8556SL / 8557SL likely?)
4) IML (?), onboard 8-bit (narrow-) SCSI, old BIOS, no fix available

You may use an additional controller and/or additional drive which exceeds 1GB. At least, the Non-IML machines should be able to boot from off a second SCSI controller which, for preference, should be one which supports drives over 1GB. The original SCSI controller needs no drive attached - but should be terminated, at least at one end, to avoid problems.
The small Server 85 with the Narrow planar SCSI will most likely need at least one drive under 1GB containing the IML partition attached to this controller.

Which systems do not exhibit the problem or can be reworked?

The following systems support drives over 1GB 'as is' without requiring a rework:

  • IBM PS/2 9556 and 9557 with onboard SCSI (1)
  • IBM PS/2 9576 and 9577 with "Bermuda" planar and onboard SCSI (1)
  • IBM PS/2 9576s and 9577s with "Lacuna" planar and IBM SCSI-2 card (2)(*)
  • IBM PS/2 9585-xKx and -xNx with onboard Fast/Wide SCSI (3)
  • IBM PS/2 8590-xMx and 8595-xMx with Type 3 CPU platform (1)
  • IBM PS/2 9590-xMx and 9595-xMx with Type 3 CPU platform (1)
  • IBM PS/2 9595(A)-xNx, -xQx, -xPx with Type 4 CPU platform (4)
  • IBM 8641-xYx Server 500 with Type 4 CPU platform (4)

1) IML machine, limited to 3.94GB for the primary drive due to IML partition.
2) Non-IML machine, supports a "service partition" containing reference and diagnostic programs for convenience. However, the drive is limited to 3.94GB when this feature is used!
3) The machine uses SurePath BIOS - but needs an IML partition nonetheless ... pretty strange. Limited to 3.94GB therefore.
4) The machines uses SurePath BIOS and needs no "system partition". Supports a "service partition" containing the reference and diagnostics programs for convenience. However, the limit is 3.94GB for the primary array on those machines which use the IBM RAID-controller to boot from!
* This machine has an onboard IDE controller, which may alternatively accept drives over 1GB - this however requires at least a BIOS Level 08 in the machines flash BIOS. The update is available here!
Remember: Using IDE instead of SCSI is a step backwards...

The following machines or their SCSI controllers can be reworked to enable them to handle drives over 1GB:

  • IBM PS/2 8550 (1)(3) and 8560 (1)
  • IBM PS/2 8555 (1)(3) and 8565 (1)
  • IBM PS/2 8570 (1)(3) and 8580 (1)
  • IBM PS/2 8590 and 8595 - all models except -xMx (1) or (2)

1) An appropriate SCSI adapter card must be used. The one already installed on the SCSI Models like 65SX and 80-Axx can be reworked. (See below)
2) Upgrade BIOS available. (See below)
3) System has no standard power plug for SCSI harddisk. See here if you have a 50/70 or here if you have a 55SX, for how to install a power plug.

Fixing the problem in the Machine BIOS

The PS/2 Models 8590 and 8595 can be fixed at the system BIOS level - in this case it is of no importance what microcode level is present on the installed SCSI adapter.

The following machine BIOS upgrades were available:

If your machine already has the corresponding BIOS version (number printed on platform EPROM) it is at the necessary level and can use drives over 1GB already.
The platform upgrade BIOS contains the enhanced SCSI support which is also included in the SCSI BIOS EPROMs 92F2244* and 92F2245*. You can do either one of the two reworks - or both.

* This requires an EPROM burner!

Fixing the problem in the SCSI Adapter BIOS

If your machine is equipped with one of these controllers they can be reworked to enable them to handle drives over 1GB:

  • IBM SCSI adapter without cache /A (card-ID 8EFE)
  • IBM SCSI adapter with cache /A old (card-ID 8EFF - has AIC-6250EL chip on card)
  • IBM SCSI adapter with cache /A new (card-ID 8EFF - has yellow 20-pin terminator)

The last one is, in most cases, already capable of handling drives over 1GB - but only if it has the 2 EPROMs P/N 92F2244 and 92F2245 present. All other microcode EPROMs are old and cannot handle drives over 1GB.
You need to replace the 2 SCSI BIOS EPROMs marked EVEN and ODD with P/N 92F2244* and 92F2245*, respectively. The third EPROM which contains the busmaster-CPU microcode must not be replaced.

* This requires an EPROM burner!

Complex BIOS Upgrade Needed for >1GB IML Drive

From Tim Clarke:
   After an extended e-mail exchange with Al Brandt, who couldn't get a machine to IML from a >1GB drive (SCSI ID 6) attached to a SCSI-1 controller w/cache but with the notorious (now infamous?) 92F2244 and 92F2245 'Enhanced SCSI BIOS' ROMs using a Type 1 complex with either of the 'older' complex BIOS ROMs (i.e. 84F9154 for SOD Type 1 and 91F9812 for non-SOD Type 1), I decided to run my own tests.
   'Enhanced IML' in the complex upgrades is the *only* way to be able to IML from a drive >1GB (and from a drive ID other than 6).
   At this time I must assume that the 92F2244+5 ROMs provide support for drives <= 4GB, but the 'old' complex ROMs' IML support somehow does not make (proper) use of it, possibly due to bad bit-shifting and/or masking when 'translating' the 'cylinder, head, sector' information to and from the SCSI 'logical block/sector' value.

System partition size on on a >1GB drives

BTW, space is usually allocated as a whole no. of cylinders, so the 'old' 3MB "System/Reference Partition" will grow to ~12MB on a >1GB drive. Albeit that only the 1st 3MB of that space is used/needed.

Using other IBM or Non-IBM SCSI controllers

On the older Non-IML PS/2 like the Mod. 50/60, 55/65 or 70/80 you could use a non-IBM controller, which must have a boot-ROM. These controllers are, for example:

  • IBM Fast SCSI-2 Adapter /A (OEM from Future Domain used in 76s / 77s)
  • Adaptec AHA-1640 and OEMs of that card
  • Buslogic / Bustek BT-640 and OEMs of that card
  • Buslogic / Bustek BT-646
  • Future Domain FD-600 / 700
  • Procom SCSI Enabler

According to Adaptec the AHA-1640 is *not* capable of booting from drives larger than 1GB under Boot-BIOS control. However, if the latest Microcode is installed (EPROMs: MCODE 7F58, BIOS 5E00), it can handle drives over 1GB under ASPI-Manager control (loaded during O/S initialisation) after booting from another sub-1GB drive.
This requires the harddisks to be formatted with the Adaptec SCSI drive formatter SCSIFMT before they are usable.
The same "bad habit" seems to apply on the Buslogic / Bustek adapters as well - I have not been able, so far, to boot from them under Boot-BIOS control - they worked fine as secondary controllers with the appropriate ASPI-Manager loaded during O/S initialisation.
The Future Domain MCS-700 adapters require a Boot-BIOS Level of 1.1 and a later ADF it seems. The older firmware levels cannot handle drives over 1GB. The Future Domain MCS-600 is (almost) identical with the IBM Fast SCSI-2 Adapter, which lacks the standard power connector and has a slightly modified BIOS to identify itself as IBM rather than Future Domain.

The above-mentioned adapters cannot be used to replace any of the IBM SCSI controllers in IML-machines. They do not have the required BIOS functions to fully support IML and, at best (with the IBM Fast SCSI-2 Adapter/A), only allow you to create a "service partition" containing the reference and diagnostic programs, for convenience. But this is not equivalent to "True IML", which loads parts of the machine BIOS from the harddisk into memory. So the IML-machines will choke with an IML-error of the I999-xxxx class when substituting one of these controllers for the IBM SCSI adapter.

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

Ardent Tool of Capitalism is maintained by Tomáš Slavotínek.
Last update: 08 May 2024 - Changelog | About | Legal & Contact