IBM PS/2 Model 70

IBM's PS/2 line was a line of computers for business applications being a next step from AT computers. They implemented many new technologies, like MCA bus, ESDI and SCSI hard disks or modular architecture composed of FRU modules, easily replaceable parts. In 1988 IBM released Model 70 with 386 processor and two years later Model 70 with 486 CPU. In fact this Model 70 had a detachable CPU daughterboard which allowed to install e.g. 386 with 387 coprocessor by just changing modules. 486DX was a relatively new CPU with math coprocessor built-in. While being expensive, it was a big improvement for CAD and computational applications. This computer is a high-end PC (sometimes it was called "Power platform", before IBM's POWER Series computers) of early 1990s.

Manufacturer IBM

Origin USA
Year of unit 1991
Year of introduction 1989
Class PS/2
CPU Intel 486DX
Speed 25MHz
RAM 6MB (72-pin SIMMs)
ROM PC BIOS, BASIC (boots if it can't boot form anything).
Setup from floppy.
Graphics VGA
Sound PC Speaker
System expansion bus MCA
Floppy/removable media drives 1x 1.44MB 3.5" FDD (proprietary edge connector).
Possible upgrade to second FDD, the same connector.

Hard disk: 120MB (proprietary edge connector, ESDI-like)

Peripherals in collection:
 - Keyboard, mouse
 - 14" monitor (non-original, probably from PS/1 Pro 2123)
 - AceCAD CAD tablet

Other cards:


MCA serial port card
Non-standard expansions: None
Operating system(s): MS-DOS.

My unit comes from some design studio, it has an AutoCAD 11 for DOS license bound to it and some designs, so Idecided not to mess with HDD contents and just keep original program. It has also drivers for HP plotter and AceCAD tablet. Probably the serial port card has been added to use the serial tablet and serial plotter the same time. It looks like this PS/2 has been used extensively since 1991 when it was bought, until late 2000. About 10 years of operation is quite much for CAD platform.

But personally, I rarely see mainboards worse than its. CPU board connector is terribly unreliable, SIMM sockets are not working well, and, hidden from users' eyes under CPU board, there are two old chips in aluminium cans. Yes, these cans which IBM used late 1970s in their mainframe products. More, the computer just can't see more than 6MB of RAM. This revision of mainboard just can't, by design. We're speaking of a high-performance platform powered by 486 (in 1991, 286 was the most popoular CPU). We have 4MB "onboard" SIMMs, which can't be moved by user and 2 free slots. It is a bit hard to get two 72-pin 1MB SIMMs. If user got 2x2MB, he would have a BIOS error on startup and unusable 2MB. Such strategy looks like making customer buy a newer hardware while preserving illusion of RAM upgrade possibility. Apple should learn from them.

And as with other PS/2s, you can see the mainboard description. Small difference: This one has 386 daughterboard installed.
And a photo showing general pinout of power supply unit. Notice that power is not high, so son't overload the system with additional devices.

Contents: Starting, usage Links


This computer is a normal PC, so it will start normally. Eventually it may jump to BASIC when it has no media to boot from. BASIC is in 128kB of its ROM. If any error is present, it will like most IBMs, display codes. See codes in IBM Codes page.

If battery is weak (battery is located in front, near speaker), the computer will need to be started from "Reference disk" floppy, pass through auto-configuration (during which it will backup raw NVRAM and CMOS RAM state in disk, so better use backups), and after next boot ask user to go to date menu and set date/time.





Links: - Collection of links - Information on salvaged website. - IBM archived site with technical specification. - PC FDD adapter. You still have to make normal FDD fit in IBM's bay somehow. - Trying to push the memory over 16MB. - How to reset password. - Hardware maintenance manual from 1994 - it consists much information about PS/2s.