The redesigned PS/2 Micro Channel SCSI Adapter Cache provides system configuration flexibility to support multiple internal and/or external SCSI devices such as high performance fixed disk drives, CD-ROM drives, tape drives, scanners, and printers. It has a burst transfer rate of 16.6MBps, adheres to the industry standard ANSI SCSI interface and is supported in either a 16- or 32-bit Micro Channel slot. 
    The IBM PS/2 Micro Channel SCSI Adapter with Cache is a 32-bit busmaster SCSI adapter containing a 512KB cache buffer that allows system memory to be totally dedicated to running the application rather than a portion being reserved for software caching. This SCSI adapter is recommended where improved data transfer rates and multiple SCSI devices are required and system memory is constrained.  However, 512KB cache is too small for the LAN Server application. 

Pin 2 of the internal port is on the component side. Pin 1 is on the circuitboard side. 

  The "single OSC"-adapter is the "old" IBM SCSI Adapter with cache /A, which has no internal termination resistor and needs the large external Terminator block.P/N is 6451018 (FCC-ID:ANO6451018).. This adapter needs the update SCSI BIOS P/N 92F2244 / 92F2245 in order to handle drives >1GB. 

Note: The Adaptec AIC-6250EL Line interface chip is just "glue logic".
   The C188 has 2x8-bit parallel-ports but only  an 8-bit external data-path. 

Ed. I saw something about potential data loss concerning this ECA. Not sure- my U47 is the adapter BIOS. 

FCC ID: ANO6451018 Mostly seen across the pond in Europe. This adapter needs the update SCSI BIOS P/N 92F2244 / 92F2245 in order to handle drives >1GB. The "dual OSC"-adapter is the "later" IBM SCSI Adapter with cache /A, which needs an external terminator. 

Ed. Odd, I have a single osc 6451018, BUT it has the solder pads and the outline for Y2. 

   The "latest" cached SCSI, FRU 85F0063 (FCC-ID is ANOSPRIME), has no Adaptec chip present and a larger yellow 20-pin DIL terminator chip close to the external port. This card has the strange 10-contact card edge connector close to the internal 50-pin card-edge. It has a third oscillator as well: a 32.0000MHz (Y3). 
   Based on Peter's experience, If you have one of the older IBM SCSI-Adapter or SCSI w/cache *cards* you can use the SCSI-Bios from the later-level SCSI Adapter with cache (92F2244 and 92F2245) to make the system capable of handling drives over 1GB IF the complex BIOS is of the correct type 

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 fixed disk 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.) 

Microcode Differences
From Charles Lasitter 
   With the triple oscillator (newest) versions of the Enhanced SCSI w/cache, I see some Microcode differences but don't see much in the way of any particular pattern for when one Microcode will be in use versus another. 
   One adapter has 10G4890 dated 1991. Another has 61G2976 dated 1993.  What is the difference between these two microcodes? I invariably see the "1993" microcode with some unusual looking cache SIMMs, but changing them doesn't seem to make a difference. I see "1993" on some boards labeled as "CARD 1" and others" CARD 3".  There is nothing I can track there. 
   I can't figure out why they would change it if they didn't make something better, but I don't know what that would be or how it would manifest itself. I know that the microcode from triple oscillator adapters can't be switched to the old unterminated adapters, but I'm uncertain about from one two another for the same "3-oscillator" family. 

From Tony Ingenoso 
   (guessing)  There may have been a change to deal with the low-power mode problems of certain microcode level Kazuza series drives...  Had to tweak the heads off the cylinder they were idled over to keep from losing data when the next write (after power restoration) happened to be on that 
cylinder...  nasty problem...OS/2 had an ABIOS patch to deal with it on the pseudo-ESDI versions of the drive. 

Making Your Own IBM Cable
  The actual cable itself is a standard SCSI-1 cable. The unusual part is the 50 pin edgecard connector ( Dalco part 40720). Note that Pin 1 on the adapter is towards the mounting bracket . Remove the 50 pin dual row header (pry it open or cut it off) and crimp on the 50 pin edgecard connector. Watch pin 1! 
   NOTE: On original IBM ribbon cables, the cable exits the edgecard connector TO THE LEFT as the connector is seated on the internal port. As installed, this means the cable goes straight up towards the top of the 95 case and away from other adapters. This makes it possible to route it away from them towards the front of the case, then down the site of the DASD structure, then to the drives. 

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 w/cache 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. 

> 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. 

Terminator Resistance Values
Fact sheet is HERE

Bourns 4120R-003, -221/331 
Model (41 = Molded DIP), 20 Pins, R = Thick Film Low Profile, 003 = Dual Terminator. Resistance Code in the format R1 / R2,  First 2 digits are significant, Third digit represents the number of zeros to follow. 220 ohm, 330 ohm. 

It looks like this.. 

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. 

From Ian Brown
   Interesting bit of history this. And no, you won't find it documented anywhere. IBM was one of the members of the organisation that originally set the standards for SCSI, and as usual they had their own ideas. 
   One of these 'unique' ideas was the ability to be able to set the SCSI ID# remotely from the host adapter rather than having to set it on the device itself. 
   The result of this was the 'legacy' small connector on some 'high end' SCSI hosts, and that awkward RS6000 socket as the external port, which became the IBM standard for a while. 
   The idea was good, but be grateful it never took off, as I understand it required decoding hardware on the devices, which could have left us looking for special 'IBM SCSI' HDD's etc. 
   It was never fully implemented as far as I know, SCAM overtook it. 

  How did I find out? I went to a 'Big Blue' re-union recently, and met one of the original designers of the IBM SCSI host adapters. I'd been wondering about that extra connector for years, so I took the opportunity to ask him. 

Specs on the SCSI w/cache

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. 

Can I increase the cache to 2MB?
One module that can be used to expand the IBM SCSI Adapter with cache /A from 512K cache to 2MB cache is the IBM P/N 30F5360 / FRU 74X8637, which is a 1MB x 9 bit (Parity) 100ns module *with* IBM-specific presence detection. 

The above-mentioned IBM modules are in the Mod. 30-286 (8530-Hxx or -Bxx) with 80286-cpu - if anywhere at all. 

MY 1MB SIMMs are marked MSC2314-12YS9A 183004 68X5721. 
It has 9 OKI M511000A-1AJ chips, mnf. 89335521 

From Jerry Dumer
I have 3 boards with Toshiba THM91010AS-10 simms that do the job fine. I found these on a memory card in a Model 60. They are gold pins. I imagine Toshiba made them for the 30-286s. They do work. 

Kingston modules labeled KTM-1000/M30 (From Peter) 

Alfred's 30-pin SIMM Hack (To his site) 
   For those that have the burden of college education, I made some assumptions. First, the SIMM pins will always  be performing the same function (like parity Data Out, parity CAS). Second, those simm pins can be used to positively identify the parity chip's DO and CAS pins. 
   This makes manufacturer's data sheets uneccessary. Assuming they even have them. 

break the connection between SIMM pin 26 and the parity chip's DataOut pin; This inferrs that SIMM pin 26 goes to Data Out- 

connect the parity chip's DataOut pin to SIMM pin 29; 
Tie the parity chip's lead that USED to go to SIMM pin 26 to SIMM pin 29 

break the connection between SIMM pin 28 and the parity chip's CAS pin; 
Parity chip CAS is attatched to SIMM pin 28 

connect the parity chip's CAS pin to SIMM pin 2; 
Attatch lead that used to go to SIMM pin 28 to SIMM pin pin 2 

connect both SIMM pins 26 and 24 to SIMM pin 22 (GND). 
SIMM 26 and 24 tied off to SIMM 22 

A picture of Dr. Jim's 2MB Hack

Results of upgrading
From an article by Peter Wendt.... 
The IBM Adapters with and without cache /A are in fact SCSI-1 adapters with 5MB/s interface speed (!) to the device. This however does not tell how high the effective data-throughput might be. 

This depends on more factors than just the interface-speed: 
- speed of the drive mechanism (track-to-track / average seek) 
- adapter-cache (size, speed and degree of optimizing) 
- device-cache (size / usage) 
- cable and degree of disturbances through line noise / spikes etc. 
- termination (reflection of data packets) 
- adapter- and device cmd set (autonomy of device / command queing) 
- the adapters chipset 

Okay - for the curiousity: I have tested the 2MB-cache in my 8595-AK9 (32MB RAM / Kingston TurboChip / modified BIOS) with 2 different IBM adapters and a Quantum Fireball TM2110S (2.1GB Ultra-SCSI). This drive is known as quite fast and should not be the bottle-neck. I used the IBM SCSI adapter with cache /A in the version *without* the internal termination resistor and the Adaptec AIC Line interface chip (IBM old) and I used the IBM SCSI Adapter with cache /A *with* the internal yellow termination resistor and the IBM SCSI Interface (IBM new). 

Here are some test-samples (results are temporary examples) 
Results for old SCSI w/cache

Results for new SCSI w/cache

Results obtained by reading and writing blocks from 512 bytes to 63.5KB in linear and random methods. 
Read Linear with large data-blocks shows a 20% gain, due to 2MB cache. 
Write Linear values are only 2 - 5% smaller in either case. 
Write Random values show the influence of the drive mechanism. 

What does this mean in practise ?
1.) Only way to get minimum values up is to use a harddisk with a faster drive mechanism.. 
2.) Combination drive - adapter doesn't reach the data-throughput for the SCSI-1 interface speed. 
3.) Any GUI operating system that uses a temporary swap file operating with large blocksizes will make use of the enlarged SCSI-Adapter cache during the swapping process. 
4.) Effects are noticeable in Win95 applications and -probably- much more noticeable on OS/2 and NT, which use the harddisk-subsystem more intensely than DOS/Windows or Win95. (That's a prediction from my experiences with these OS) 
5.) If you cannot -by what reason- use a F/W-adapter / F/W-drive combination (or don't want to) the enlarged cache to 2MB is one simple method to get out around 10 - 20% better performance of an unmodified system running under i.e. Win95 (I'd kept this careful - you cannot await wonders if you have a slow harddrive) 

 The testing will continue as soon as possible. Like very often my job came in the way and I needed the 95 (which is usually my network-server) for the daily purposes again. But this first testing suite shows that the enlarged cache *has* in fact a good impact on the over-all performance of the system. I'll try to fix up the results and try bringing them here - if you like "data cemetries"... the tables are *very* complex and have hundreds of numbers, which must be set in proper relation to each others. And must be interpreted the correct way. 

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.