The new short adapter is functionally equivalent to the earlier full length version and the on-board termination scheme is the same.  The differences between the two cards besides the length are: 

1.  Short card firmware (Spock Prime) can handle the SCSI2 command set 
2.  Long card firmware (Tribble) CAN NOT handle SCSI-2 Command set. 

Speed
   The SCSI /A long card will do 6.6 Mbps 

°   IBM Personal System/2 Micro Channel SCSI Adapter 

       The PS/2 Micro Channel SCSI Adapter is a 16-bit Micro Channel bus master adapter that provides the ability to connect multiple SCSI devices to all PS/2 Micro Channel systems. This Micro Channel SCSI adapter adheres to the industry standard SCSI interface. It features an 8.3MB per second burst data transfer rate, 16-bit data path with 32-bit address capabilities, and can be installed in either a 16- or 32-bit system card slot.  A SCSI physical device could be a fixed disk, scanner, plotter, printer, CD-ROM, or controller. 
     The bus master capability of this SCSI adapter optimizes data flow from each SCSI device configured to the system. This capability can provide performance benefits in applications where multitasking or high-speed data flow is essential. It allows the processor to be off-loaded from many of the input/output activities common to DASD transfers. This SCSI Adapter also conforms to the Subsystem Control Block (SCB) architecture for Micro Channel bus master. 

New BIOS Improvements (From Tim Clarke) 
> Oh, really? Please expound on the "extra features" of the new SCSI bios. In addition to handling drives >1GB as the IML drive, what else? 

The upgrade provides the following additional capabilities: 
  1. More efficient use of Adapter ROM memory - minimizes adapter configuration conflicts. 
  2. BIOS support for fixed disks up to 3.94 gigabytes per device. 
  3. Supports "Search IML" from any PUN (Physical Unit Number) or 
     SCSI ID.  The system partition is no longer restricted to only SCSI 
     ID=6.  Each HD ID will be searched for a valid system  partition. 
  4. Allows redundant system partitions (IML). 
  5. Sharing of SCSI devices.  An external SCSI device, such as the 3511, 
     may be shared between two system units. The menu item is "Target" 

> So what good is the multiple, redundant partitions? Especially  with a T1-3 complex? 
    If drive id. 6 fails 'recovery' can be automatic without the need to recover IML-capability by partially ripping the machine down to change SCSI Id.s.  You do, however, need to have planned for this and set up the appropriate 'IML/Reference Partition'(s) and 'Active Partition'(s) on the 'fallback' drives (Id. 5, 4, 3... etc.) 

SCSI Device Ordering
   Older SCSI adapters supported only a single bus which provided both internal and external SCSI bus connectors for the single bus.  For these adapters, devices are logically ordered depending only on adapter slot  number and the SCSI IDs of the devices. 

Multiple SCSI Device Order
From Bob
    Now, i got 4-1gb 0662's w/cd-rom  in my 9595-omt-- the problem is 
this--win3.1 does'nt see all of these only 2 -0662's and cd-rom. Ref 
disk sees all 5 w/cd-rom. I just added 2 0662's and not sure what's on 
them. I tried "fdisk" and "dos" but their not there. Any suggestions? 
Scsi "id's" are as follows. 
id-1 0662 
id-2 0662 
id-3 cd-rom 
id-4 0662 
id-5 0662 

From Brad Parker
Hi Bob, 

Using the ANSI/IBM standard, I would set the ID's as follows: 

id 6 boot drive (c) 
id 5 2nd hd (d) 
id 4 3rd hd (e) 
id 3 4th hd (f) 
id 2 CD ROM (g) 

   Because the standard gives the greatest SCSI bus priority to the highest 
numbered drive and the lowest priority for the lowest numbered drive. If 
you have more than one partition on each drive, then the drive letters may 
change, but the device IDs will stay the same. In fact, I might just set 
the CD to id 0 to give yourself room for future expansion :-) 

   I have five HDs, three floppies, a 6 disc changer and a Zip drive on one 
of my 95s, of course I have two host adapters.... 

Maximum SCSI Devices Supported
  Narrow SCSI devices support 8 possible SCSI ID values; therefore, up to 7 narrow SCSI devices can be connected to the internal or external SCSI busses in any combination using the remaining ID values.  Wide and narrow devices may be mixed on the same internal/external bus by using the proper combinations of SCSI bus cables, terminators, and/or SCSI connector convertor adapters. 

 Is the SCSI /A SCSI-2?
   The SCSI adapter on the 8595 is "SCSI-2 compliant" - means: it uses parts of the *command set* from SCSI-2 (command queueing, command tagging) but the *transfer speed* is SCSI-1 with 5MB/s. It is also a "Narrow"-SCSI controller - opposed to "Wide"-SCSI, which means it uses 8-bit devices and not 16-bit devices. 
   However: it can handle even Ultra-SCSI drives, because SCSI is compatible in any directions - other than shit-IDE. 
   And the controller is "Single Ended", which means that every signal has GND as return line. "Differential" means, that every signal has a return line with inversed polarity ... when -for example- +DATA0 sends a logical "1" on the active line the return line -DATA0 sends a logical "0". The transceiver circuit in the device checks the *difference* between the two signals (therefore "differential") - line disturbances afflict both lines at once and are eliminated therefore. 
   Conclusion: the IBM SCSI adapter is 8-bit narrow, single-ended SCSI with SCSI-2 style command set and SCSI-1 speed of 5MB/s. It can handle 7 Fast- or Ultra-SCSI devices and can handle even 7 Wide-devices if there are converters used from Wide-to-narrow SCSI (68-to-50 pin) but these devices must use device numbers from 0 - 6. The SCSI-ID 7 is used for the controller itself. First device on IBM SCSI controllers is the one with the highest ID (6) opposed to Adaptec or Buslogic controllers. 

ECA 032 Explanation
   The old non-cached adapter can be identified by the FRU 15F6561on the lower left hand corner of the component side of the card. Some adapters may have been updated. 
   The old card, Y1 is 25MHz and Y2 is 20 MHz. On the updated adapters, Y1 is 20MHz and Y2 is 12.5MHz. Yellow wires may or may not exist on any level of the card. If PN 85F0002 is present, it is the latest level and does not need to be replaced. If you have either of these versions of the 15F6561, replace them. 

Joe Kovacs says 
> The original IBm 32-bit SCSI (without cache) worked OK with HDs, but lost bits with CDROMs.  So an engineering change was specified, and it was patched with a couple of wires in the upper right hand corner, becoming an 85F0002.. 

My retort- 
   The reworked 15F6561 cards I have seen have the rework wires just about dead center (FAIR). Not sure if this is it... 

> Peter, for the $64,000 Question. If you use a yellow termpack on a  adapter or board that had a red one initially, will that enable it  to autoterminate? 

   Definitely: No. The "Auto-Terminate" is a function that require a little more hardware: a switching transistor that disables the TermPwr wire from the T-RES and another transistor / IC function that senses the voltage on the TermPwr line and the voltage on the data lines to figure out whether the line is terminated or not. 

Termpack FRU
From Tim Clarke
   AFAIK, there is only one FRU for the "internal" termination resistor pack for  the IBM SCSI w/cache (adapter FRU 85F0063) that has the appropriate 20-pin socket and  the IBM SCSI w/o cache (adapter FRU 85F0002).  The termination resistor pack (20-pin) is FRU 57F2870 and, provided you insert it with Pin 1 correctly oriented, should work O.K. 

Enable Termpower or Not?
From Peter 
   Back in the "good old times" there was a fairly common problem with the TERMPWR: if you had an external box and the device was set to supply TERMPWR as well as the adapter it could happen that the external device tries to feed back +5V via TERMPWR line into the controller once the "computer" was turned off. Which often fried the cable and / or blew the TERMPWR fuse(s). 
   The later standard defined the TERMPWR circuit as a "fuse / diode" combo:- the fuse (pico fuse or PTC / auto-reset fuse) to protect the adapter / device against short-circuits on the TERMPWR line and the diode to prevent backflow of +5V from external devices to the controller. 
   So *normally* there should be no problem to have TERMPWR enabled on all devices - which makes sense on setups with very long cables and multiple external devices. The importance of TERMPWR is often underestimated in SCSI-1 environment. Here it is pretty important to feed the TERMPWR line from *at least* one device to have the proper pull-up on the signal lines at all. On SCSI-2, where each device *should* have its own active termination and *should* monitor the TERMPWR and set the termination accordingly it is of lesser importance. In the worst case one device supplies the termination at least - if not the host adapter itself. 
   The main problem occurs, when the TERMPWR line on SCSI-1 setup is interrupted beween two devices and none of the devices supplies TERMPWR: in this case a proper termination cannot be achieved, because the (passive) terminator at the end of the chain has no TERMPWR to act on. 

Multiple installed IBM SCSI MC/A (w/o Cache) Adapter
   If more than one IBM MC/A SCSI Adapter (FRU P/N 85F0002 or 15F6561) is installed in a MC-System, and during setup two or more adapters are shown with same PU/LU setup, or SCSI HD-drives connected to this card(s) are not correct responding, check the EPROM's in position X5 (ZM5). The EPROM-P/N in position X5 should be 41G9974. 
   Ed. Not sure what this means. None of the SCSI Adapters I have use the mentioned EPROM. Good or bad? 

Pinouts for the SCSI /A and the SCSI w/Cache
  The edgecard for the SCSI Adapter /A has less contacts than the later SCSI w/Cache. Still wondering why... But you can see a tableized version (Thank you, thank you..) of Peter Wendt's observations. It is HERE. 

15F6561   The long, uncached adapter... This link is to an ECA that concerns a mandatory replacement... 

80C32GB- 10MHz microcontroller as busmaster CPU 

J3 Serial Port 
   Made up name. This is a status link header like on the late SCSI w/cache. From left to right, the pinout is CHR, ITS, BRN, TXD, RXD, GND 

T-Res for Short SCSI/A
   I finally got two primo condition short SCSI/A controllers. They both have a yellow termpack, Bourn 4120R-003 -221/331. This means they have autotermination. 

   The short card has been built by IBM to fulfill longer running service contracts on old machines after production of the long uncached adapter ran out. The BIOS is located top / left, two small chips with 92F2244 and 92F2245. These are the same P/N as used on the "later" cached SCSI Adapter  and already contain the upgraded code for IML drives up to 3.94GB. The adaptercard itself is an interesting mix of components from the uncached (long) and later cached (long) SCSI adapters. Works nicely. 

Today - while juggeling around with parts & cards on a Model 90 - I decided by what reason to remove the SCSI-Bios from an old uncached SCSI and stuff that from the "later" cached on it. Earlier this year I'd tried to swap the entire Eprom-Sets among the old and the later cached - and it did not work. Today I left the busmaster microcode Eprom on the card and only swapped the SCSI-Bios. 

To my undescribeable surprise: it worked. 
  To make sure that it is not a gimmick of that machines' Bios I tried it on a Mod. 70-A21, which has definitely no enhanced SCSI-Bios support in the planar microcode. I pulled the 2GB IBM 0664 harddisk from my WinNT Server and installed it in the Mod. 70. I have a heavily modified Mod. 70 - has a standard power-plug (as described on my page, folks !) and a Kingston 486DX-33 upgrade. I also installed the uncached SCSI with the old Eproms. No surprise: "No operating system" and the system halted. 

Then I used the 92F2244 and 92F2245 on that same adapter ... Voilà: "OS Loader V4.00 ..." and WinNT 4.0 Server started up ... ! (Ever seen that on a Mod. 70 ?) Tried the same procedure with the old IBM SCSI adapter with cache (the one *with* the AIC-6250EL Line Interface) - with the same results.  Old Bios-chips: No operating system - New chips: Win NT starts 

Conclusion: If you have one of the older SCSI-Adapter *cards* you can use the SCSI-Bios from the later-level SCSI Adapter with cache to make the system capable to handle drives over 1GB.

I do *not* know if there is another limit after 4GB - but assume it is (I don't have drives over 2.2GB currently). This limitation will at least exist on the IML-machines, since the principle that starts up the IML cannot handle drives over 3.94GB (the mysterious IML-border) due to the technical method of putting the systempartition MBR at *the end* of the physical diskspace. The register width is obviously limited to any number of total data-blocks below 4GB. So that does not change at all. 

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. ¬= 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. 

From another thread
    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. 

Some Other Thoughts
From Charles Lasitter
   I've had some VERY entertaining results in my installations, depending on what other drives were present, and which version of the processor BIOS was used. 
   With the 52G9509 in place, ID6 in bottom bay (Mod 95) at end of cable, ID5 in bay above on next spot on cable, I couldn't get the IML to go to ID6 to save my ass.  It made a beeline for ID5 every time.  Put in the old BIOS, and it goes straight for ID6. 
   I think there are a LOT of quirks like this (and yours) to be mapped out, and that seemingly innocuous settings changes in the ABIOS make differences you'd never guess sometimes. 
   I also suspect that the Mod 90 is it's very own distinct bird with it's own eccentricities in this and related matters. 

I/O Address
    I/O address for adapter. Each adapter must have a unique address range
       <"3540-3547">, 3548-354F, 3550-3557, 3558-355F, 3560-3567, 3568-356F, 3570-3577, 3578-357F

DMA Arbitration Level
   DMA channel used to transfer data.
      < "Level C">, D, E, 8, 9, B, 1, 3, 5, 6, 7

Fairness On/Off
   Bus Arbitration Fairness.  Whether the adapter will release control of the bus when it has been using it exclusively
          <"On">, Off"

ROM Wait State Disable
   Whether a wait state is added to accesses of the ROM on the adapter.
          <"Enable Wait State>, No Wait State

SCSI Adapter Address (ID)
   SCSI ID of the adapter
      <"7">, 6, 5, 4, 3, 2, 1, 0"

ADPItem 1 ROM Address Range
   This field shows the address of the 32K block of memory that is
assigned to the adapter.  Only one SCSI Adapter will have the ROM
assigned, and any other SCSI Adapter installed will share that
address range. If the ESDI adapter is also installed, then the address of the SCSI adapter must be greater than the ESDI adapter address.