Memory, Cache, Features
Min/Max on system board: 8/64MB 
RAM: DRAM (PS/2 72-pin SIMM) Interleaved (Install SIMMs in pairs) 70ns parity checked 
   Although 80 and 85 nanosecond (ns) memory Single In-Line Memory Modules (SIMMs) are supported, 70ns memory SIMMs provide optimum memory performance.
ROM: 128kb 
Cache: 8kb L1, optional 256kb L2 J and K complexes 
* Socket for optional L2 256K write-through memory cache on "J", "K", and  "Upgrade" DX2-66 (256 K write-thru standard with 486DX-50 ).
* No math coprocessor socket on "J", "K", and  "Upgrade"  complexes.
* 24 bit DMA; 10-12 MHz. (10-12? One or the other, please)
* Dual path memory design (Dual Bus Interleave).
* 20 MB per second data transfer support (for MCA bus)

Side Toward Complex

Side Away From Complex

256 KB Cache Memory Option Kit, 6451095 (64F0199 same thing) $ 19.95 They are HERE

L2 Cache Performance
From Us, the god-Emperor of Microchannel
   Praytell, what use can one make of the 256K cache for the T1 complexes? I hate to admit it, but I never noticed a large (or significant) boost when I added one. 

From Tony Ingenoso
   The effects of modern bloatware on a write-through can be disheartening... IMO IBM's matched cycle scheme goes a long way towards helping keep the L1 lines filled at a brisk pace even when no L2 is present.  The T2's abnormally good performance (considering its other genetic limitations) shows this well.  For all practical purposes, 90/95's have a 64 bit memory subsystem working to fill the L1 lines.

From Charles Lasitter
   What do you see with one speed processors (DX50) that are coupled with a faster cache 64F0050, or the T3 and integrated cache? Since they don't have a 'fall back' processing speed in the event of an L1 miss, but rather use a 12ns L2 vs 17ns, is there any difference for them?
   I believe we've seen LARGE increases in speed when doing something like kernel rebuilds compared to no cache.  I think it may depend on what you're doing and the operating system.

From Tony
   I don't see this as a core multiplier issue -- even the low end DX25 T2 runs better than one might expect it to. The kernel rebuild improvements aren't suprising - compilation algorithms and the bits of data they work tend to be well localized if modules aren't too massive.  Initial parsing would be very read intensive as well and should make good use of an L2. Cache perf is indeed a very task specific kind of thing.  Scattered code/data can effectively neutralize it totally.
   DX50's are strange -- they often outrun DX2-66 when main memory bandwidth or I/O is the constraint.  When staying in L1, then the DX2-66 wins due to the multiplier.   With a fast L2 and fairly scattered code/data a DX50 is going to do very well.

From Peter
   Uhmmm ... I had the occasion to test a T1 DX2-33/66 board under Linux. And compare it with the same T1 DX-50 (!) board - both with the L2 cache. 
   The 486DX2-33/66 showed 33 BogoMips, the DX50 25 only ... same as the T3 DX50 while a DX2-50/100 (Intel DX4-100 in 2x mode) on a T3-platform runs at -supposed- 50 Bogomips almost.
   In the practical use the T1 DX50 wasn't much slower than the T1 DX2 - the XF86 stuff paced at the same rate on both. None of the machines "felt" faster or slower. The DX4 T3 was a bit faster - but not significantly. All 3 machines had the same XGA-2 card, the same TR 16/4 network adapter, the same 32MB Parity RAM and the same IBM 400MB HD with the Linux on it.
   The T1 platforms had the "plug on" 256K L2 cache (17ns on the DX2, 12ns on the DX50) and the T3 had its own integrated cache. I did not write down all the values ... maybe I should repeat that session again to get some definite, comparable data.

SCSI drives >1GB as IML
Type 1 complexes (with the exception of the DX2-66 Upgrade, 92F0145) need a BIOS 52G9509 to handle IML drives of >1,023MB. (EPROM in drawing)
  The upgrade provides the following additional capabilities:
  1. Adapter ROM memory more efficiently utilized to minimize 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=3D6.  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 following models are affected:
  1. Only the following processor boards with an EPROM module label having the following part    numbers may be upgraded:

PROCESSOR  FRU P/N   MODEL     EPROM P/N            LOC.
20MHZ SX   92F0049   0GX        91F9812             U36
25MHZ DX   64F0201   0JX       84F9154 OR 91F9812   U36
33MHZ DX   64F0198   0KX       84F9154 OR 91F9812   U36
50MHZ DX   92F0048   P3 (UPGD) 91F9812              U44
  It was called the "8590/95 Dual Booting Capability EPROM Package" 

 Type 1         PART NUMBER 52G9509 (was 52G9750 - try this if other PN is not known)

  NOTE:  Use the latest refdisk and diags. See above...

57F2194ESD  Memory Controller
78F1659(A)    Memory Data Buffer
78F1659(B)    Memory Data Buffer
78F1659(C)    MCA Buffer
63F7520          DMA Controller
   On the 20-MHz board, the jumper 2 must be in positions 1 and 2 if a 487SX processor is installed in connector 3 . If there isn't a 487SX in connector 3 , the jumper must be in positions 2 and 3.

© Copyright IBM Corp.

 20 and 25 Mhz Processor Boards
   For SX models, you can install an optional processor on a 20 or 25 MHz processor board. 
  The 25-MHz processor board (above right) has a second processor connector 3 for either an optional 487SX processor or an 80486SX 25/50 MHz processor. If you install an option processor in connector 3 , of the 25 MHz board, you do not have to remove the existing processor (it is overridden). 
   Carefully insert the tip of a screwdriver between the processor and the connector edge and gently twist the screwdriver (around all edges) until the processor raises up. 

NOTE: When you reinstall the processor, align the beveled corner 1 with the beveled corner marked on the board. 

"K" 486DX 33 MHz 64F0198

57F2194        Memory Controller
78F1659(A)  Memory Data Buffer
78F1659(B)  Memory Data Buffer
78F1659(C)  MCA Buffer
90X8134       DMA Controller (Same as in Type 0 and the 50Z planar)

DX33 Complex. Solder pads are the mark of the SOD. If your complex doen't have them, it is not affected. Non-SOD complexes support a Turbochip. (well, usually. IBM made SO many different revisions...)

What is the SOD?
> What exactly is this square of death? (SOD)?
It is the mark of the beast. This square of solder pads is actually the binary equivalent of 666.

From Peter
  The socket layout from the S.O.D. does not match a 486 layout. It is one row of pins smaller - so it anything else but *not* 487 or suchlike.
   There is an IBM ASIC (silver EMC shield capped type) that comes as close as one can be with the two (!) pins missing in one row. So I assume they had made room on the early Type 1 platforms for another of these ASICs - and it later turned out that they don't need or want it.
   Again: the artifact S.O.D. is not a 486/487 layout !

SOD Limitations from Tim Clarke
   The limitation of the 'poor DMA controller' for the Type-1 SOD board appears to be that you can't run a Cyrix/IBM 5x86 at greater that 'x2 clocking' (i.e. 50Mhz in a Type-2, 66Mhz in a Type-1) or an AMD 586 at greater than 'x3 clocking' (i.e. 75Mhz in a Type-2, 100Mhz in a Type-1). Ed. You CAN run a 486DX4-100 ODPR on a SOD. It's only a 3x multiplier.
   Not having a SOD Type-2 I can't test this, but I would expect the same limits to apply. So, you should be able to run a DX2-50, DX2-ODPR (@ 50Mhz), Cyrix/IBM 5x86 (@50Mhz) or AMD 586 (@ 75Mhz) in a SOD Type-2. The 'performance' of a Cyrix/IBM 5x86 @ 'x2 clocking' and the AMD 586 @ 'x3 clocking' are *roughly* equal, although I have a preference for the Cyrix/IBM chip.

J4- Once you toggle this jumper you will end up in a 0129 3000 error - "EEprom Jumper is in the wrong position" and no boot or such. I'd reported that some time ago while testing around with the 92F0145.
  Most likely it was originally intended to give the -0145 with 2 banks of EEprom to choose between - but by what reason they installed only one bank and the alternative setting branches into a BIOS error-code instead.

Peter sez:
   As a follow up notice: Yes - it *has* a flash-BIOS. And - Yes - it comes up with the Type-1 reference disk. Even installs a reference partition as usual with these disks.
   But the system permanently fails to boot into this Type 1 reference partition. Once you reboot it and press [ctrl]+[alt]+[ins] at CP 66 (cursor top / right) the machine loads the operating system instead jumping into reference.
   The platform nicely takes the Kingston Turbochip *without* restoration of the system partition. Runs fine with it - right from the start.

Supports Non-IML Configurations
  Dennis Smith found out that this complex can successfully boot without an IML device at ID6. He booted a SCSI drive at ID0 WITH NO IML track. I did it here with my upgrade DX2-66.
   His guess was this complex was designed to support RAID Arrays, and the early RAID controller, "Passplay" had no ability to boot from an array.

Some observations-
The chipset appears to be the same as other Type 1s. There is an addition of decoding circuitry.

FCC ID- ANOIBM486A50
This uses the standard Type 1 EPROM

L2 Cache- 92F0050
NOTE: This complex needs the 15nS cache. The other Type 1 complexes use 17nS memory.

From Peter
Hi Louis !
   As far as I can tell (from the pictures of that complex) it varies through some different wiring and modified ASICs. The part of the hardware that deals with the CPU clock generation looks a bit different. The rest of the card is the "later" Non-SOD Type 1 platform as I have it here in my trusty old AKD.
   It seems as if IBM wanted to offer an upgrade path to DX-50 *without* the ECC option - for those customers that have a -xKx machine already and for the Mod. 90 maybe, which does not cope with the "2 layers" DX-50 Type 3 platform very well.
   This board was not offered with any particular Mod. 90 / 95 right from the start. It has been an option only.