Terminating the IBM SCSI-1 Adapters
General SCSI-cabling rules
Adapters that can handle >1GB
Can my controller handle >1GB?
Duplexing SCSI Drives
IML considerations
Why Do IBM Controllers Boot From ID6?
Connecting Narrow Devices to a Wide Host Adapter (Adaptec site)

SCSI Adapters - Problem determination
Windows 98 Compatibility - SCSI Adapters
SCSI Adapters - An introduction to SCSI devices
Adding a SCSI fast wide device to a SCSI fast and  narrow controller

ASPI4B.SYS - DOS ASPI Driver for IBM SCSI .Supports the IBM SCSI BIOS (interrupt 4B) interface. Supports CDs and scanners. I have no other device types to test it with, but it should support tapes and other devices...

Terminating the IBM SCSI-1 Adapters
   Just as ST-506 and ESDI adapters need a terminating resistor (T-RES) on the last drive, so the SCSI adapters must be told where to find the "end of the line."
   The 16-bit PS/2 SCSI Adapter includes a T-RES terminator chip on the adapter. This chip must remain in the following instances:
    1. If no physical devices (also called PUNs, for Physical Unit Numbers) are connected to the adapter, because it is not currently being used.
    2. If the PUNs are all internally attached, or all externally attached.

  The T-RES chip must be removed if internal and external PUNs are attached. In this case in-line terminators (which come with the option cables) are used between the last internal and external PUNs and the cables connecting them to the next-to-last PUNs (or the adapter, if the PUN is the only internal or external device on the chain).
    For example, to connect two internal and three external PUNs, the internal devices would be daisy-chained from the internal 50-pin edge-connector, while the external devices would daisy-chain from the 60-pin D-shell connector on the back of the card. If either the internal devices or the external devices are all removed, the T-RES chip would be needed on the adapter. All the terminators needed are included with the various components; however, should the T-RES chip be removed (and lost), but be needed at a later date, a replacement may be ordered as a service part (FRU part number 57F2870).
   32-bit SCSI Adapter with Cache The original 32-bit PS/2 SCSI Adapter with Cache is different in the respect that it does not come with an onboard T-RES chip. There is a separate external terminator (Part number 6451039) which must be used if no external devices are attached. Later shipments of the PS/2 SCSI Adapter with Cache were redesigned to be similar to the PS/2 SCSI Adapter in that it too has an onboard terminator, eliminating the need for an external one. The new adapter can be easily identified by the bright orange terminator on the adapter.

General SCSI-cabling rules
 NEVER connect a second cable, to make a longer SCSI cable with either INTERNAL -or- EXTERNAL  devices. You have to use a longer cable (do not try to solder cables).

 Never make a T -or- Y SCSI adapter-connection. Such an SCSI-bus cannot be correctly terminated !

Rule of thumb with drives over 1GB:
- if the machine is a mod. 90 or 95 with processor platform type 3 (-xMx) and 4 (-xNx, -xQx and -xPx) it will support drives over 1GB. If it is a Type 1 (-xGx, -xJx or -xKx) or Type 2 platform (-xHx and -xLx) it requires a BIOS 52G9509 (type 1) or 41G9361 (type 2) to make it capable for over 1GB; the type of SCSI adapter is unimportant in that case, since the *machine BIOS* supplies the code

Other adapters to support drives over 1GB are
- IBM Fast SCSI-2 Adapter /A  (card-ID 60E9, re-badged FD MCS-700)
- IBM Fast/Wide Adapter /A     (card-ID 8EFC)
- Future Domain MCS-700        (card-ID 60E9)
- Adaptec AHA-1640 with microcode 7F58 / bios 5E00
          (card-ID 0F1F; rebadged as SDC1611 / Tecmar SCSI)
- Buslogic BT-640A with latest microcode and ADF
          (card-ID 0708 with option "DOS Disk Space >1GB" to "On")
-Storage Dimensions SDC3211B with latest microcode and ADF  2.3 
       (card-ID 0708 OEM'd BT-640A w/"1GB Translation" set to "On")
- Buslogic BT-646S = Bustek BT646S = Storage Dimension SDC3211F
          (card-ID 0709 with the option "1GB Translation" set to "On")

Special considerations for IML!
IML-machines (90 / 95) are able to load the IML-code from >1GB drives as well *until the size does not* exceed 3.94GB ! This is the general limitation on the size of the drive holding the IML-partition.

Why Do IBM Controllers Boot From ID6?
>Ahhh, another ibmism.....  Will it boot from any other address or must it boot from ID 6?

IBM used the ANSI-compatible boot order, which was the original standard booting down (!) from the controller (ID7) to the next drive (ID6) and so on. Other companies like Adaptec choosed to have the controller at ID7 too but boot *up* from the lowest-numbered drive at ID0 (which is all ID-jumpers removed). Don't know why. Individualism most likely. While Adaptec was the "major key-player" in the SCSI league everyone in the world believed that this were the proper order to boot SCSI-drives - but isn't. Look into the original ANSI X3T papers and you will find that booting down from 6 - 0 was the original *recommendation* of the ANSI SCSI committee.

Duplexing SCSI Drives  (Type 4 only, others require moving the working adapter to Slot 1)
If you are setting up a SCSI-equipped PS/2 system for duplex operation, install a second SCSI controller, and all drives and options that will be in the system.  One drive on the second controller should be set for SCSI ID 6.  This will enable the system to boot from this drive in the event of failure. Be sure to copy all Option Diskettes to the system partition and then follow the steps below. 

   1. Boot the system to the system partition and configure the system as necessary. If anything has to be changed manually, this is the time to do it.  It will save much time later. 
   2. Insert a blank 1.44MB diskette in drive A:.  (It will become a Reference Diskette.) 
   3. Back up the system partition to the blank Reference Diskette. 
   4. Turn the system off and swap the SCSI cables at the controller end.  (This will make the new drive the boot drive from the original adapter.) 
   5. Boot to the Reference Diskette just made, and restore the system partition to the new drive. 

 If the drives are the same, the system will not need to be reconfigured.  To simplify recovery in the event of failure it is recommended that 1) the drives be of the same capacity on both controllers, 2) both controllers have the same number of physical drives, and 3) the addresses be set the same on both the adapters and the drives.  (Each adapter has, for example, SCSI ID 7 for the controller, SCSI ID 6 for the first drive on each controller, SCSI ID 5 for the second drive on each controller and so forth.)  This enables the system to be brought back up without having to be reconfigured in some cases. 

 In the event of drive failure, the cables can be swapped at the controller end to get the system back in operation.  In the event of a controller failure, the failing controller can be removed. Remember, both drives have system partitions on them, but the drive set to SCSI ID 6, and attached to the SCSI adapter in the lowest numbered slot is the only one that can load the system partition.  If we remove the adapter from slot 1, the system will boot from the adapter in slot 2.  The system will need to be reconfigured, but that can be done from the existing system partition on the backup drive. 

 If any drive or controller is removed, the system will need to be reconfigured, but if the system is powered down and the defective 
 component is swapped with a good component of the same specification, the system will not need to be reconfigured. 

P.S. For OS/2 duplexing/mirroring software, check out IBM's LAN Server 4.0, or Integra Technologies' OASAS I 2.0, or EZRAID from Pro Engineering.