PS2 FAQ - Motherboards

Archive-name: PS2-FAQ - Motherboards
Last-modified: 1996/02/20
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Version: 4.0
Author: Chris Feeny <Alkemyst>

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S) 2.0 Motherboards

Q) 2.1 Where can I find a PS/2 motherboard?

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 whether from IBM or a third-party dealer often times at the low-end $700, DakTech 800-325-3238 has new ones.. Used motherboards can be obtained from Page Computers 800-866-0055 for a reasonable price ($250 for a PS/2 model 80 20MHz board and $138 for the 4MB of RAM to go with it). I have bought two boards from them and have had no problems with either. The people working there are normally ex-IBM PS/2 people who know alot more than your average computer salvage types. Your best bet in general is to pick up a Computer Shopper and scan the pages for PS/2 stuff and put the numbers in a easy to find database (and also send new numbers found to me for FAQ additions) so that whenever a problem arises you can look up the company that sells what you need.

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

Reply Technologies (800-955-5295) sells new PS/2-type motherboards much cheaper than the IBM versions. These are 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.

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

. Also Kingston Technologies has motherboards, but at the time of this writing I do not know what they offer.

These motherboards usually include memory sockets, SVGA on board, and some a P24T upgrade socket. In general these are very modern designs and offer a major performance gain, especially those for the model 50 line. The Reply motherboards also offer a MCA VLB slot for their own VLB card.

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

No...unless you are VERY lucky(and probably 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 stratch.

Q) 2.4 What motherboards come with a cache and are more up-to-date with todays standards?

Well I am not going to be able to complete this section but 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.

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.

16 BIT
Model Factory Installed Max - Motherboard Max - System
35/40-all 2 16 16
50-021 1 2 16
50Z-031 1 8 16
50Z-061 2 8 16
53 ***
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
Model Factory Installed Max Motherboard Max System
95 70-061 2 6 16
95 70-081 4 6 16
95 70-121 2 6 16
95 70-161 4 6 16
95 70-A16 4 8 16
95 70-A21 2 6 16
95 70-A61 2 8 16
95 70-A81 4 8 16
95 70-E61 2 8 16
95 70 486-B21 2 8 16
95 70 486-B61 2 8 16
95 76 ***
95 77 ***
95 80-041 1 2 16
95 80-071 2 2 16
95 80-081 4 4 16
95 80-111 2 4 16
95 80-121 2 4 16
95 80-161 4 4 16
95 80-311 2 4 16
95 80-321 2 4 16
95 80-A16 4 8 16
95 80-A21 4 8 16
95 80-A31 4 8 16
95 90 XP 486-0J5 8 64 64
95 90 XP 486-0J9 8 64 64
95 90 XP 486-0KD 8 64 64
95 90 XP 486-0J5 8 64 64
95 90 XP 486SX-0G5 4 64 64
95 90 XP 486SX-0G9 4 64 64
95 90 XP 486SX-0H5 8 64 64
95 90 XP 486SX-0H9 8 64 64
95 90 XP 486SX-0K9 8 64 64
95 90 XP 486SX-0KF 8 64 64
95 95 XP 486-0G9 4 64 64
95 95 XP 486-0GF * 64 64
95 95 XP 486-0J9 8 64 64
95 95 XP 486-0JD 8 64 64
95 95 XP 486-0JF 8 64 64
95 95 XP 486-0KD 8 64 64
95 95 XP 486SX-0H9 8 64 64
95 XP 486SX-0HD 8 64 64
Model Factory Installed Max Motherboard Max System
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
* Entries not in ASCII original - HTML editor's note

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

Nope, neither. There are reports of some using non-PS/2 72-pin SIMMS, but these have not been verified by myself and also I suspect that they are actually third party PS/2 SIMMS the user was unknowingly using.

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.

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 (ie 50's and 60's) and most 386s can get by with 85ns, 85ns, those less than 25MHz. 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.

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 independant 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 emmission. 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 maximium transfer rates on a 10 MHz MCA bus:

(Transfer Type ) 16-bit MCA 32-bit MCA
Normal transfers (adr/data) 10MBytes/sec 20 MBytes/sec
Short Burst and Long Streaming transfers (adr/data data data ..) 20MBytes/sec 40 MBytes/sec
Multiplex Streaming (as above and uses the `idle' adr lines to transfer data as well, or a 64-bit transfer) (not available) 80 MBytes/sec

     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 16 Mhz 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 (100 ns for the address and 100 ns 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 200 ns 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".

IBM has also disclosed that upcoming generations of Micro Channel systems may implement a faster basic transfer cycle of 100 ns rather 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.


Also it has been quoted that MCA does not have to be tied down to the bus and speeds up to 40MHz were said to be short term goals. I wonder if any third- party vendors will give this a shot as it would be *FASTER* than VLB and possibly most PCI.

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:
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 (aka. 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 adaptors, but its high cost limits its usefulness for other types of cards.

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.

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.

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 availible 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.

email:Chris Feeny\

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