PS/2 FAQ, Section 2

S) 2.0 Motherboards

Q) 2.1  Where can I find a PS/2 motherboard? (Not fully verified 04/24/00)

PS/2 last a long time, but sometimes due to mother nature, the user or just age the motherboards (planar boards in IBM-speak) fail.  These can be obtained in many places both new and used.  Beware that the price of a new motherboard is steep from IBM. Some third-party dealers have them much cheaper than in the past.  DakTech (800-325-3238) carries some either new or as good as new form with a warranty. Check first, their stock varies.  True Blue Parts 508-833-2225 ( formally Micro Mart has the Model 80-Axx board for only $60. 

Q) 2.2  Instead of a 'stock' motherboard can I get a more advanced board?

Speak of the Devil.. Genesis Technology makes a motherboard replacement for the 55SX/LS which includes a new slot assembly and the motherboard. Unfortunately, it's ISA. 

Reply Technologies sold new PS/2-type motherboards much cheaper than the IBM versions.  These were high priced compared to normal PC-Clone motherboards, but if you have cash in memory and PS/2 proprietary items it is cheaper than replacing everything with new ISA/VLB/PCI based equipment. Also they offered Pentium processors, the ability to use standard SIMMs, and even VLB.  These are still available used and new on . The types of motherboards available from IBM are the 486DX2/66 and 486BL2/66, and almost every 486 type from Reply Technologies. The IBM motherboards are only available from the Boulder Surplus Parts division and are limited as they are no longer being made.  Also they were made only for the 60, 65SX, 70 and 80. 

There is a model 50/50Z and 55SX/LS planar board upgrade to 486SLC2/50 available currently from IBM.  Note: these were discontinued in Sept 94 so they are limited, if IBM Direct doesn't have them call Boulder. 

There are two versions of Reply's motherboards: the TurboBoard (for models 30, 50/50Z, 55SX, and 70) and the PowerBoard (for models 25/25-286, 30-286, 50/50Z, 55SX, 56 and 57, and 70).  Using the model 70 as the example, the TurboBoard offers a 486SLC2 25/50 CPU, 387SX FPU socket, 16MB max using 3 70ns parity SIMMs, on board 1MB DRAM video, and 3 16 bit slots (one with video extension).  The PowerBoard offers 486DX2/66, 486DX4/100, or 586/100 with Intel Overdrive socket, 64MB max using 3 70ns parity SIMMs, on-board 1MB (2MB upgrade) 64 bit local bus video, two 32 bit and one 16 bit (with video extension) slots.  This is not a bad way to go. 

There are no more Reply motherboards at Neointeractive. 04/24/00 

Q) 2.3  Will a standard motherboard work in a PS/2?

No...unless you are VERY lucky(and probably the only one in the world).  Most times the screw holes will not even come close, then the slots will be way off.  Even if you got it fastened into your case you would need a new power supply (which you would have to screw in some how) and then new floppy drives etc.  You are better off selling the system and starting from scratch. 
  A hack was done with a PCI clone board into a 9595 case, but it involved MUCH hacksaw work, installation of a clone power supply, jury-rigged motherboard mounting (screwholes DID NOT line up) and MUCH duct tape (the handyman's secret weapon!). 

Q) 2.4  What planars come with cache and are more up-to-date with today's standards?

The model 70 and 80s with a 25MHz processor (8570/8580-Axx) come with a 64k L2 cache which is very helpful.  Benchmarks on a 20MHz model 80 and 25MHz model 80 with the cache showed Dhrystones at 4k for the 20MHz and at 7.7k for the 25MHz which is a bigger difference than the 5MHz should give by itself.  As a matter of fact a Cyrix DRx2-40 processor in a 20MHz machine gave only 8k Dhrystones, a cache of some sort should always be obtained when purchasing a motherboard. 
   The Lacuna planar 9576 and 9577 systems (on-board S3 video) have an L2 cache socket that takes either 128KB or 256K COAST modules. The 9585 -xKx and -xNx models use a similar cache module. 

Q) 2.5  Which motherboards allow/prohibit additional on-board memory?

The following list shows what memory can be added.  The difference of the Max System and Max Mother is what must be installed in the form of an expansion card. 

                         Factory    Max    Max 
Model                   Installed  Mother System
16 BIT
35/40-all                   2       16      16 
50-021                      1        2      16
50Z-031                     1        8      16
50Z-061                     2        8      16
55LS-LE0                    4        8      16
55LS-LT0                    4        8      16
55SX-031                    4        8      16
55SX-041                    4        8      16
55SX-061                    4        8      16 
55SX-081                    4        8      16
57SX-045                    4       16      16
57SX-049                    4       16      16
60-041                      1        1      16
60-071                      1        1      16
65SX-061                    2        8      16
65SX-121                    2        8      16
65SX-321                    2        8      16
32 BIT 
70-061                      2        6      16
70-081                      4        6      16
70-121                      2        6      16
70-161                      4        6      16
70-A16                      4        8      16
70-A21                      2        6      16
70-A61                      2        8      16
70-A81                      4        8      16
70-E61                      2        8      16
70 486-B21                  2        8      16
70 486-B61                  2        8      16
80-041                      1        2      16 
80-071                      2        2      16
80-081                      4        4      16
80-111                      2        4      16
80-121                      2        4      16
80-161                      4        4      16
80-311                      2        4      16
80-321                      2        4      16
80-A16                      4        8      16
80-A21                      4        8      16
80-A31                      4        8      16
90 XP 386DX20-O0x
859x XP 486/959x Models
90/95 486SX20   xGx        4       64     64      Parity
90/95 486DX33   xKx        8       64     64      Parity
90/95 486DX25   xJx        8       64     64      Parity
90/95 486SX25   xHx        8       64     64      Parity, Single SIMM spt
90/95 486DX2-50 xLx        4       64     64      Parity, Single SIMM spt
90/95 486DX-50  xMx        4       64     64/256  Parity or ECC
90/95 486DX-50  N/A        4       64     64      Parity (Upgrade T1)
90/95 486DX2-66 N/A        4       64     64      Parity (Upgrade T1)
90/95 486DX2-66 xNx        4       64     64/256  Parity or ECC
90/95 586-60    xPx        4       64     64/256  Parity or ECC
90/95 586-66    xQx        4       64     64/256  Parity or ECC
90/95 586-90    xYx        4       64     64/256  Parity or ECC
P70 386-031                 2        8      16
P70 386-061                 4        8      16
P70 386-121                 4        8      16
P75 486-161                 8       16      16
P75 486-401                 8       16      16

Max mother is what can be physically added to the motherboard.  Max system is what can be added in the form of memory cards.  Max system is also the maximum memory of the mother and expansion card combined. 
   New information shows that it IS possible to use a memory expansion card in a 90 / 95 / 85 system, BUT the extra memory is NOT cached by the L2 cache controller. Any reads will be SLOWER by far than planar memory. 

Q) 2.6  Can I use normal 72-pin SIMMs?  30-pin SIMMs?

  You can alter standard 72 pin Fast Page Mode SIMMs by adding the Presence Detect to them. This involves soldering a little blob across a few pins. Go to Peter Wendt's site for details. 

Q) 2.7  How do I tell the speed of the PS/2 SIMMs I have now on my motherboard?

Most of the times unless labeled it will be hard.  IBM's numbering system changes all the time and many times the cross-reference can not be made.  I got a SIMM here that has a nice label stating IBM  2M  85NS  P/N 68X6127  FRU 92F0104.  Now if that label were removed I would only have 89X8922 IBM9314 L46056PE on the 18 chips that are attached to the SIMM, now if someone can make 2M or 85NS out of those three numbers I would be impressed as a call to 
IBM showed it as not identifiable. 

In  OS/2 WARP there is a program that tells what is installed and the speed of the SIMMs.  This program is the system information utility.  Although it would be impractical for a large amount of unlabeled SIMMs, a few can be ID'ed this way. 

According to Louis Ohland <>: 

The 9595 Type 4 (possibly type 3) can report in setup on the speed and architecture (parity or ECC) of each chip by slot... 

Q) 2.8  What speed SIMMs do I need? 

Unlike buying clone motherboards, the speed of the SIMMs you should need will usually be easily found out.  For standard IBM, call IBM and for all other motherboard makers they should include it in their motherboard docs.  Most of the time the 80ns memory is the most common on the newer machines.  120ns was used on the older PS/2s (i.e. 50's and 60's) and most 386s at or less than  25MHz can get by with 85ns.  If you upgrade to one of the new 486 replacement  386 CPUs you will probably need 80ns memory unless stated that it will work with normal system memory, 70ns and faster is probably a good idea and should be used as 80ns and slower memory is becoming obsolete. 

From Louis Ohland <>: 

The 90 / 95 / 85 prefer 70nS, but will tolerate 80nS. If you use a mixed pair of 70 and 80, the memory controller will use both at 80nS. You can hack a 60nS SIMM to work (adding Presence Detect), but the 60nS speed is not supported by the BIOS (nor is it a valid value of Presence Detect!), and the SIMM will be accessed no faster than 70nS. 

Q) 2.9  How good is MCA and what does it offer?

IBM is pushing the MCA bus again.  It is possible to make it as fast as VLB, it comes close now.  The new 700 machines will offer a dual bus, MCA/PCI which will give the best of both worlds.  The *BEST* thing about MCA is it usually offers the PLUG-and-PLAY everyone wants, at least in most cases.  You simply copy the .ADF files onto your reference disk then plug the new card in 
and turn on your system.  The computer will figure out where the card is and configure it and for once you don't have to set 10 banks of 8 dipswitchs with a pen :).  Also it offers the best bus mastering out there.  A MCA card can totally take over all functions of the CPU and FPU and cause no interference with the rest of the machine, also a MCA board can have its own CPU to do the work of the peripheral it is attached.  For example lets say you had a MCA Video Toaster type could be set up to allow you to configure certain  options, enter data, then have it process the data no matter how complex and  return to your normal machine and witness no slowdown at ALL.  MCA allows card functions to be totally independent and self-controlled. 

A problem faced by ISA was device addresses, and ISA bus is only capable of 1024 device addresses while MCA can address 65,280.  Also, MCA has far more  grounds along the bus preventing radio emission.   Lastly, MCA can share interrupts while ISA can not. 

The speed of MCA is something underestimated by non-PS/2 users.  It is a very fast and quiet (as far as RF interference goes).  Some specs are: 

     The maximum transfer rates on a 10 MHz MCA bus: 

                                 16 bit MCA       32 bit MCA 
     Normal transfers           10MBytes/sec     20 MBytes/sec 

     Short Burst and Long 
     Streaming transfers        20MBytes/sec     40 MBytes/sec 
     (adr/data data data ..) 

     Multiplex Streaming       (not available)   80 MBytes/sec 
     (as above and uses the 
      `idle' adr lines to 
      transfer data as well, 
      for a 64 bit transfer) 

     Matched Memory Cycle                        21.3 MBytes/sec 
     (matched memory cycle 
      changes the timing of                     (32 MBytes/sec w/o 
      the MCA bus to 62.5                        added wait state 
      nanosec. for a 187.5                       at 62.5 Nanosec. 
      4 byte adr-wait-data                       and 40 MBytes/sec 
      transfer cycle. This                       with 50 nanosec 
      is on a 16MHz model                        timing) 
      80 as an example.) 


Since there have been so many discussions about all of this, I'm posting the OFFICIAL MCA specs.  These are direct from IBM.  MCA, as you will notice, has the capability to be faster than even the local bus technologies with a  transfer rate of up to 160MB/sec.  Hope all of this helps. 

The basic transfer cycle on the Micro Channel is a minimum of 200ns (100ns for the address and 100ns for the data which results in five million basic transfer cycles per second for a device running in burst mode.  As shown in Figure "Basic Data Transfer Mode", a data transfer operation is done in two steps.  First the address for the transfer (either I/O adapter or memory location) is selected, then up to four bytes of data is moved across the data buffer. 

Depending of the width of the data path (8, 16, or 32 bits) the instantaneous data transfer rate on the channel would be 5, 10, or 20MB per second.  The matched-memory extension is a modification to the basic data transfer mode, which can improve the data transfer capabilities between the system master and channel-attached memory.  When supported, it allows the basic transfer cycle of 200ns to be reduced. 

The DMA controller on the system board requires two basic transfer cycles to move either 8 bits or 16 bits of data.  It moves the data from the originator to a buffer in the DMA controller and then to the target device or memory location.  Because two cycles are used per 8 or 16 bits of data, the data transfer rate for DMA controllers is 2.5MB or 5MB per second.  For blocks of 
sequential data transferred over the Micro Channel, it should not be necessary to specify the address information more than once.  Both the source and destination devices should update the address for each cycle by the size of the transferred data.  This technique is supported by the Micro Channel and is known as streaming data mode (or streaming data procedure).  Using streaming data mode with 32 bit transfer, the effective transfer rate is 40MB per second.  The usage of the address and data buses during a data transfer using streaming data procedure is shown in Figure "Streaming Data Mode". 

When the Micro Channel is running in streaming data mode, the 32 address lines are only used during the first cycle of the transfer.  These address lines are therefore available for transfer of an additional four bytes during each following cycle.  This mode is called multiplexed streaming data mode and gives an effective width of 64 bits (8 bytes) for each cycle.  The resulting effective data rate is 80MB per second.  This is shown in Figure "Multiplexed Streaming Data Mode". 

PS/2 Model 9595 (and possibly the 8595) can support the 100ns basic transfer cycle with the SCSI Fast/Wide adapterrather than the current 200ns.  With the current cycle the Micro Channel is able to transfer sequential blocks of data with transfer rates of 20, 40, and 80MB per second. 

Systems implementing the faster transfer cycle would be able to reach transfer speeds of up to 160MB per second.  These rates are essential for advanced function bus masters, which must move large blocks of sequential data. 

Q) 2.10  Which is better, ISA/EISA/VLB/PCI/etc? 

[From: (Ralph Valentino)] 
[updated: 10/23/94] 

Here is a quick overview of the various bus architectures available for the PC and some of the strengths and weaknesses of each.  Some terms are described in more detail at the bottom. 

XT bus: Bus originally used in the IBM XT. 
        8 data bits, 20 address bits 
        4.77 MHz 

   Comments: Obsolete, very similar to ISA bus, many XT cards will work in ISA slots. 

ISA bus: Industry Standard Architecture bus (a.k.a. AT bus) 
        8/16 data bits, 24 address bits (16Meg addressable) 
        8-8.33MHz, asynchronous 
        5.55M/s burst 
        bus master support 
        edge triggered TTL interrupts (IRQs) - no sharing 
        low cost 

   Comments: Ideal for low to mid bandwidth cards, though lack of IRQs can 
             quickly become annoying. 

MCA bus: Micro Channel Architecture bus 
        16/32 data bit, 32 address bits 
        10-20MHz, up to 40MHz could be possible, asynchronous 
        80M/s burst, synchronous 
        full bus master capability 
        good bus arbitration 
        auto configurable 
        IBM proprietary (not ISA/EISA/VLB compatible) 

   Comments: Since MCA was proprietary, EISA was formed to compete with it. 
             EISA gained much more acceptance; MCA is all but dead. 

EISA bus: Enhanced Industry Standard Architecture bus 
        32 data bits, 32 address bits 
        8-8.33MHz, synchronous 
        32M/s burst (sustained) 
        full bus master capability 
        good bus arbitration 
        auto configurable 
        sharable IRQs, DMA channels 
        backward compatible with ISA 
        some acceptance outside of the PC architecture 
        high cost 

   Comments: EISA is great for high bandwidth bus mastering cards such as 
             SCSI host adapters, but its high cost limits its usefulness for 
             Other types of cards.  Very commonly used in servers. 

VLB: VESA Local Bus 
        32 data bits, 32 address bits 
        25-40MHz, asynchronous 
        130M/s burst (sustained is closer to 32M/s) 
        bus master capability 
        will coexist with ISA/EISA 
        slot limited to 2 or 3 cards typical 
        backward compatible with ISA 
        moderate cost 

   Comments: VLB is great for video cards, but its lack of a good bus arbiter 
             limits its usefulness for bus mastering cards and its moderate 
             cost limits its usefulness for low to mid bandwidth cards. 
             Since it can coexist with EISA/ISA, a combination of all three 
             types of cards usually works best. 

PCI:  Peripheral Component Interconnect 
        32 data bits (64 bit option), 32 address bits (64 bit option) 
        up to 33MHz, synchronous 
        120M/s burst (sustained) (240M/s with 64 bit option) 
        full bus master capability 
        good bus arbitration 
        up to 6 peripherals 
        auto configurable 
        will coexist with ISA/EISA/MCA as well as another PCI bus 
        strong acceptance outside of the PC architecture 
        moderate cost 

   Comments: Combines the speed of VLB with the advanced arbitration of EISA. 
             Great for both video cards and bus mastering SCSI/network cards. 

VL 2.0: Video Local Bus version 2.0 
        64 data bits, multiplexing and data buffering 
        up to 50MHz 
        est. 400M/s burst 
        full bus mastering 
        good bus arbitration 
        specification not completed yet 


Auto configurable:  Allows software to identify the board's requirements and  resolve any potential resource conflicts (IRQ/DMA/address/BIOS/etc). 

Bus master support:  Capable of First Party DMA transfers. 

Full bus master capability:  Can support any First Party cycle from any device, including another CPU. 

Good bus arbitration:  Fair bus access during conflicts, no need to back off  unless another device needs the bus.  This prevents  CPU starvation while allowing a single device to use 100% of the available bandwidth.  Other buses let a card hold the bus until it decides to release it and attempts to prevent starvation by having an active card voluntarily release the bus periodically ("bus on time") and remain off the bus for a period of time ("bus off time") to give other devices, including the CPU, a chance even if they don't want it. 

16Meg addressable:  This limits first party DMA transfers to the lower 16 Meg of address space.  There are various software methods to overcome this problem when more than 16 Megs of main memory are available.  This has no effect on the ability of the processor to reach all of main memory. 

Backward compatible with ISA:  Allows you to place an ISA card in the slot of  a more advanced bus.  Note, however, that the ISA card does not get any benefit from being In an advanced slot, instead, the slot reverts To an ISA slot.  Other slots are unaffected. 

The MCA specs at 10MHz show sustained throughput very close to VLB and 20MHz MCA specs should be equal or superior to VLB, however, usually MCA cards do not operate at these faster speeds of 20MHz. 


8088  8086      286            386              486                 586 
              AT bus 
PC bus 

1982  1983  1984  1985  1986  1987  1988  1989  1990  1991  1992   1993 

Q) 2.11  Will an ISA card work in an MCA (PS/2) machine? 

No, they will not.  MCA, unlike EISA and VLB, is not backward compatible with ISA.Some dual bus cards exist (DCA network card, ATI Ultra 8514/A) but these cards are specially designed to flip over and use the correct edge connector. There WAS an ISA to MCA module for the 286 based Gearbox. Chances are, most 286 Gearboxes were scrapped. So much for hope... 

Q) 2.12  How do I enter the CMOS configuration menu? 

If it is possible on your machine it is Ctrl-Alt-Ins after Ctrl-Alt-Del.  If nothing happens when you hit Ctrl-Alt-Ins at the prompt then you must use the reference disk to change CMOS values. 

   On the flash BIOS based systems, when the Surepath BIOS splash screen pops up, press F1. 
    On IML 90 and 95 systems, at CP 62 the cursor *should* jump to the top / right position on the screen Press the keys CTRL + ALT + INS. The interval for this is pretty short though - only a few seconds.- all other models show the CP-Codes in the bottom line of the screen. However: some are not shown logically, during the time the screen is blanked and the video subsystem is disabled. 
    On other IML systems, the cursor *should* jump to the top / right position on the screen on all  IML-machines. Press the keys CTRL + ALT + INS. The interval for this is pretty short though - only a few seconds.  9556, 9576, 9577 

Q) 2.13  What is bus mastering anyway? 

Bus mastering is the ability of the MCA card to directly read and write to main memory.  This allows the CPU do delegate I/O work out to the cards,  freeing it to do other things.  If you want a bus mastering card, you should specifically request it and expect to pay more.  Also not all cards are available in bus mastering form due to the fact that they do not have to be independent to the rest of the system, and some because they can't be independent. 
    You will not see any benefit from busmasters unless the system is heavily loaded.

9595 Main Page