Type 1 Complex
rf90951a Type 1 Refdisk
rd9095a Diagnostics (common to all T1-4)

Type 1 BIOS Images  
84F9154 for SOD Type 1 with socket -OR- solder pads  for Weitek 4167
91F9812 for Non-SOD Type 1 with nothing but SMDs or resist to right of CPU.
52G9509  "8590/95 Dual Booting Capability EPROM"

AM27C010-155DC 1 Megabit (131,072 x 8-Bit) CMOS EPROM

SCSIFIX.ZIP Finally! A utility to alter the number of sectors for a SCSI drive and convert them to a 3.94GB drive! Bob Eager, you have answered a prayer!

        Memory supported, cache, features
        256K Cache Daughtercard for Type 1
           L2 Cache Performance
        ODP vs. ODPR
        Complex BIOS Upgrade Needed for >1GB IML Drive 
           Upgrade EPROM Additional Capabilities
        Complex EPROM Speeds  
        Type 1 Complexi Upgrade to "8590/95 Dual Booting Capability EPROM"  
"G" 486SX 20 MHz
       "G" Processor Upgrade
"J" 486DX 25 MHz 64F0201
      Tracking 4167 Capable Complexi
      Info on Weitek 4167

"K" 486DX 33 MHz 64F0198
     What is the Square Of Death?
       Square of Death Limits
     ECA 0530 0Kx complexes with Complex P/N 84F9356

Upgrade 486DX2 66/33  92F0145
        Supports Non-IML!
Upgrade 486DX 50 MHz  92F0048

Common Features of the Type1

20MHz DMA and MCA Bus interface.
Socket for 256K L2 Cache daughtercard (except "G" complex)
Memory controller can access up to 64MB of planar memory
DMA controller originally limited to 16MB. Fixed by the last BIOS update  (unknown how)
Memory controller supports parity, matched SIMMs only.

"G" 486SX 20 MHz
J2 SX / DX
20.0000 MHz Osc
U7 57F2194 Memory Controller
U16, 20 78F1659 Memory Data Buffer
U30 78F1659 MCA Buffer
U36 BIOS (AM27C010)
U38 90X8134 DMA Controller0

   On the 20-MHz board, jumper 2 must be on 1 and 2 if a 487SX processor is installed in position U1 . If there isn't a 487SX in U1 , the jumper must be on 2 and 3.

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

256 KB Cache Memory Option Kit,  6451095 (64F0199 same thing)

17nS for 25 and 33 MHz complexi, 12nS for 50 MHz complex.

The 256 KB cache is an add-on to the processor adapter. It is a 5.5 x 3.0 inch card that connects to either the processor adapter 25 MHz or the processor adapter 33 MHz. The connection is made up of 160 pins arranged in four columns and 40 rows. The processor adapter provides all the power required to drive the 256 KB cache.

256 KB cache memory option three basic logic elements:
   256 KB of SRAM
   4 KB of TAG SRAM
   A cache controller.

  256 KB of Static Random Access Memory ["Data SRAM"]. This is two-way set associative, which allows each index location in the cache to store two pieces of information. This improves the hit ratio, and decreases the number of times that cache items must be removed to make room for new items.

  4 KB of "TAG SRAM" stores some of the cache item's address bits, used to store and locate the item, and some bits used for validity checking.

  "Cache Controller" coordinates access to the SRAM. On a cache-hit, the controller organizes the access of the data from the data SRAM using the TAG SRAM address. On a cache-miss, the controller places the new data into the cache, updating the TAG SRAM and data SRAM at the correct index location.
  The controller is also responsible for ensuring that the address being searched for is actually a cacheable address. If not, no cache search will be done.

Optional Cache Card Installation
The installation of the 256 KB cache is as easy as plugging it into the corresponding  attachment on the processor adapter. One pin, called the "key", has been removed to provide a guide for inserting the card correctly. 

256K Cache Not Visible under System programs?

After installing the 256 KB cache, the processor will simply begin to use the cache. It will not appear in the configuration of the system. The only time you will see the L2 Cache in a message is when it is malfunctioning.
256K 17nS Cache Daughtercard

Side Toward Complex
J1 159 Pin Header  AMP 650754-1
TD1  Fil-Mag 77Z14A030
TD2, TD4 Fil-Mag 77Z14A025
TD5, TD6 Fil-Mag 77Z14A045
U18-U21 SDT 74FCT646ASO
U22, U23 TIT031XS AS573A
U24-U27 Toshiba TC55329J-17

Side Away From Complex
U1-U4  Toshiba TC55329J-17
U5,6,8 TI SN74ACT 2160-17FM
U10 AMD 64F6043
U11 AMD 84F8257
U12 AMD 64F6065
U13 AMD 84F8261
U14 AMD 64F6046
U15 AMD 64F6048
U16 AMD 84F7970
U17 AMD 64F6066
Ed. The chips change from module to module. Yours may be different.

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 15ns 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 surprising - 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 performance 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 DX2, 15ns on 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.

   169 pin ODP - 487SX installed with 486SX still in place, needs the "SX-disable" pin. Important on boards with soldered CPU.
   168 pin ODPR - (R - "Replace") replaces 486SX / 486DX does not need "SX-disable" pin.

Complex BIOS Upgrade Needed for >1GB IML Drive 
   Type 1 complexes require the combination of BIOS 52G9509 and SCSI BIOS 92F2244/45 in order to handle IML drives >1GB (new limit is 3.94GB). The upgrade BIOS incorporates the 'Enhanced IML' which supports IML from a drive >1GB and "search IML" which allows IML from a drive other than ID6. The SCSI BIOS 44/45 pair supports drives well over 8GB. [Ed. You OS may have other ideas...]

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.

Enhanced BIOS Effects
From Charles Lasitter
   As a result of a programming project with Mr. Clarke, I am now fairly certain that the odd behavior of an IBM SCSI controller "ignoring" ID6 to lay an IML track on a drive that was ID5 was really a function of the enhanced BIOS, which sniffs out the signature of any current or previous IML partition on a series of drives, and insists upon installing or recovering a system partition to that same location.

   This same feature is related to the IBM controller's inability to do an actual format of the drive if there has been an IML partition on the drive before.  The space at the end of the drive is never released, because the IBM controller refuses for format that area of the drive.

   That's why I typically use the RAID adapter when I REALLY want to nuke some drives. 

Upgrade EPROM Additional Capabilities  
    Type 1 complexes (except DX2-66 Upgrade, 92F0145) need BIOS 52G9509 to handle IML drives of >1,023MB. (U36 in drawing)
  1. More efficient use of Adapter ROM memory minimizes adapter configuration conflicts.
  2. BIOS support for IML drives up to 3.94 gigabytes per device.
  3. Supports "Search IML" from any PUN (Physical Unit Number) or SCSI ID.  System partition 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, (ex. 3511),  may be shared between two system units.

Complex EPROM Speeds  
   The normal EPROM speed is -120nS (or so). Other than the fact that the second stage of POST is contained on a mechanical device, how fast is stage 1 completed?

Peter replies:
   Original chips got 120 or 150ns where the total read cycle time does not even reach that. Depending on the wait states during BIOS access I would dare the guess that it is closer to 250ns for each word read. And while the ROM read speed is dependent on the total processor board cycle times it cannot be sped up somehow.

It is like using ZR-spec tires on an old '67 Mustang that would not even come close to the 300 km/h allowed for these tires ...

As you noted: the next part of the boot up runs off the HD but also at very carefully selected transfer speeds to allow even the slowest HD to cope with it. I don't think that using a faster HD (or FDD as well) would speed up the process significantly. The boot process has been designed to be carried out under worst case conditions to allow debugging or running a diagnostic tool afterwards (like CTRL-A). All of that includes a lot wait loops. If I were a better programmer I would flea out the BIOS for these and run it under the assumption that the HD could keep pace and get in the data as fast as possible ... and if *that* fails retry in a slower mode.  As far as I know they don't even use DMA to access the media but PIO.

Type 1 Complexi Upgrade to "8590/95 Dual Booting Capability EPROM"
  Complexi with the following EPROM part numbers may be upgraded:

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" 

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

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

"J" 486DX 25 MHz 64F0201 (old 84F8036)

OS1 25.0000 MHz Osc
OS2 20.0000 MHz Osc
U7 57F2194 Memory Controller
U8 142 pin PGA socket for Weitek
U16, 20
78F1659 Memory Data Buffer
U16, 20 54F2958 Memory Data Buffer (old)
Socket for 17nS L2 option
U30 54F2958 MCA Buffer (old)
U30 78F1659 MCA Buffer
U36 BIOS (AM27C010)
U38 90X8134 DMA Controller

The J complex has been seen in three guises:
   142 pin socket for Weitek 4167
   Solder pads, but no socket SOD)
   No solder pads

Tracking 4167 Capable Complexi
Looking into the functionality of a Weiteck 4167 "Abacus" in the U8 position. From this VERY limited sample, it seems you need 54F2958 Memory Data Buffer (old) in U16, 20, and 30 to support the Weitek 4167.

Special J (J with 4167 socket)
PCB 84F8036 026
Small sticker on Weitek socket "Kit 34"
Complex BIOS "IBM Confidential" U2IT16 84F9155 18 June 90
54F2958 Memory Data Buffer (old)
57F2194 Memory Controller

Not So Special J (4167 socket) Lorenzo Mollicone sent some pix,
84F8208 (handwritten on sticker)
BIOS 64F6032, 1990
54F2958 Memory Data Buffer (old)

Info on Weitek 4167
Weitek Abacus FPU by Axel Muhr
WeitekDisk.zip  Test suite from Weitek

Applications that took advantage of the Weitek Abacus were scarce. AutoShade, Autodesk Renderman, 3-D Studio were the most prominent to use a Weitek coprocessor. If you happen to own one, you might actually use or at least test it so heres the official test-suite from Weitek. If contains these tools

    DOS TSR to update the BIOS for Abacus support (if missing)
    Test tool which checks for an Abacus presence using INT 11h BIOS calls.
    Diagnostic tool
    2 demos: Side-by-side Mandelbrot benchmark and rendering Phong shaded beach ball
    Abacus macros for using it natively in your cool assembly code

copro16a.txt  The best source of technical information about the 4167 is the highly recommended copro16a.txt by Norbert Juffa in 1994.

4167 Floating-Point Coprocessor advanced data 

"K" 486DX 33 MHz 64F0198

OS1 33.0000 MHz Osc
OS2 20.0000 MHz Osc
U7 57F2194 Memory Controller
U8 142 pin socket
SOD or bare
U16, 20 78F1659 Memory Data Buffer
U19 Socket for 17nS L2 cache option
U30 78F1659 MCA Buffer
U36 BIOS (AM27C010)
U38 90X8134 DMA Controller

The K complex has been seen in three guises:
   142 pin socket for Weitek 4167
   Solder pads, but no socket (SOD)
   No solder pads 

"Special K" (American breakfast cereal)
BIOS 84F9155 "IBM Confidential"
PCB is marked 64F5785 01 (right above U7)
54F2958 Memory Data Buffer (old)

Not So Special K
BIOS 84F9154 (unknown if 4167 flavored)
PCB is marked 64F5785 01
78F1659 Memory Data Buffer

It appears they share the same PCB, one has "IBM Confidential" / 54F2958, the other 84F9154 / 78F1659 (84F9154 likely a straight 486 BIOS)

Non-SOD Ks (Nothing where U8 was, just green resist)
FRU 64F0198
PCB is 92F1186 01
BIOS is 91F9812 (NOT Dual Booting Capability EPROM)
Uses the 78F1659 Memory Data Buffer

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.

David Beem responds:
     The missing A1 & A2 pins make this a dead giveaway for the Weitek 4167. Steven Wachtel reports "memory management" problems (ECA #0530) with the SOD complex, which might make sense since the Weitek processors use high memory areas to transfer op codes. So, can a socket go in place to see if a 4167 would be functional there, or was it a dropped option? I suppose that with a couple SOD T1s (one of each of the patches talked about in this thread) & a Weitek 4167 I am one of those that could answer the question.

>Regarding the sensitivity of this complex, has anyone ever tried to swap the BIOS with another Type 1 complex that is known to work with the faster CPUs?

     Despite the complexi being very similar & using the same reference disk, fundamental changes for things like the Weitek coprocessor could really mess things up. IBM would issue a whole complex if there was problems, not just a BIOS change. Other than the T4 'N' I have seen no evidence of other complex types checking things like CPUID.

Peter adds:
   The only reflection from the past is the comment of an IBM employee confronted with that exact question. He said "Forget about it". He then added that the complex had been designed at a time when IBM was yet "Big Blue" and tended not to give too much control over their products to one OEM and they therefore integrated provisions for a "non-Intel" MCU (the Weitek), but the full integration never came.

   Practically the SOD can be judged as an analog to the "spare" dual-in-line artifact solder spots that can be found on many cards, where the developers planned to build "something" but weren't sure what it could be and how it should look. Reserve spots in a way suitable for add-ons or patches, barely attached to the whole board - apart from power, GND and some basic address / data / signal lines. The outline matches the Weitek math-co, but it is (after my knowledge) not supported from neither the glue logic nor the platform BIOS.

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.

ECA #0530 90-0K9/95-0KD with Complex P/N 84F9356

Steven Wachtel wrote:

   These systems appear to have a memory management problem. In my environment it was seen on a Model 90 with 16 MB of RAM. The system would hang during OS2 boot or during invocation of simple processes after a basic install (such as the system editor ). Symptoms at other OS2 sites would include excessive "random" trap errors. Not using DOS on these systems, I would expect the problem to surface as some indeterminate memory related failure in the E/XMS region.

    During initial setup of this machine, the problem appeared as an inability to create a usable backup reference disk ( if said disk was used there were always errors ).  On restart after the failure the machine will request to exec its own auto-reconfiguration and mark out the "bad" regions.  For my situation I had the IBM CE on-site for ~6 days for two separate events.  The CE changed each memory chip and riser (for the M90) multiple times and recombined them in every combination representation. 

   Today (11/5/91) after following his instincts and direction of the higher level support reps, he contacted them again. They asked for the part number of the CPU board, upon which rests a Gate Array based custom memory controller.  He was advised that there are *known* problems with the down-rev boards in my new machines. This problem exists(ed?) on the 0KD models of the M90 and M95, and possibly (as I do not have any to verify this ) the 0JD models.  IBM's second level support is apparently aware of this potential problem, but has not disseminated this to the CE level or the purchasing customer. 

Problem part identification and rectification:
   If the Processor Complex ( nee-CPU board ) part number is 84F9356 ( or 84F anything ? ) on the "barcode/label" of the board you should get a replacement. 
   The replacement part bears the part number 92F.....  I do not know if this is free.  Note, I have a M95 with this later board version that has never shown any of these problems.

Upgrade 486DX2-66  92F0145

OS1 33.0000 MHz Osc
OS2 20.0000 MHz Osc
U7 57F2194 Memory Controller
U8 space for 142 pin PGA socket
U16, 20 78F1659 Memory Data Buffer
U19 Socket for 17nS L2 cache option
U30 78F1659 MCA Buffer
U36 ???
U38 90X8134 DMA Controller

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.

Upgrade 486DX 50 MHz  92F0048

OS1 50.0000 MHz Osc
OS2 20.0000 MHz Osc
U1 486DX-50 CPU
U7 57F2194 Memory Controller
U8 Solder pads for 142 pin PGA socket

U16, 20 78F1659 Memory Data Buffer
U19 Socket for 15nS L2 cache option
U30 78F1659 MCA Buffer
U36 BIOS (AM27C010)
U38 90X8134 DMA Controller

Some observations-
The chipset appears the same as other Type 1s with the addition of decoding circuitry.

This uses the standard Type 1 EPROM, 27010 / 27C010

12nS L2 Cache- 92F0050
NOTE: This complex needs the 12nS cache. The other Type 1 complexes use 17nS memory.

The following is for the M complex, not the Type 1 486DX-50. The PS/2 Enhanced 486/50 Processor Upgrade Option requires a unique reference diskette identified by a '3' on the label.


In addition, it implements the 40MB/second streaming data introduced on the 8595-0MF and -0MT. Better system performance and more efficient memory utilization are afforded through Enhanced Memory Optimization between memory and the Micro Channel.  The Intel i80486  50MHz microprocessor includes an internal memory cache controller, 8KB memory cache and an integrated floating-point processor unit.

Additionally, an external 256KB level-two cache is provided on the processor complex as a standard feature.  Memory must be either all ECC or all parity and must be installed in matched pairs of the same size, type and speed.

From Peter
   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. 

Memory, Cache, Features
Min/Max on system board: 8/64MB 
RAM: PS/2 FPM 72-pin SIMM. Interleaved (Install SIMMs in pairs) 70ns parity checked 
   80 and 85 (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 17nS L2 256K write-through memory cache on "J", "K", and  "Upgrade" DX2-66 (15nS L2 256K write-through memory cache on 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)

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