Another PDP11 on your desk

Thinking about the recent thread on Electronica, I remembered the Terak computer. It was a desktop with graphics and keyboard (Although from what I recall, and reading the Wikipedia page) it wasn’t that light.

It featured the LSI11 chipset, so essentially a PDP11 and predominantly ran the UCSD P-System.

Although I didn’t use it myself, there were 2 in a lab at Edinburgh University (George Square?) I worked in briefly on a summer project in 1980. I was working on an Apple II and I think there were some other systems in the room too - the common thing was that they all ran the UCSD P-system.

There was a network, but I don’t recall much about it - a shared drive with a VHS tape recorder to act as backup.

Here’s the Wikipedia page:




I haven’t checked if it is the case for this particular machine, but some computers that used this chipset had a different microcode that implemented the p-code virtual machine of UCSD Pascal directly and so were not at all PDP-11 compatible. Western Digital marketed this as the “Pascal Microengine”.


Interesting - I wasn’t aware of the Pascal Microengine… However the Wikipedia article does suggest they could run Unix v6 at a pinch, but I don’t know if they had reloadable microcode or not…


I think the chipset used specially designed ROMs for the microcode, so you couldn’t change that. When using the PDP-11 microcode you could still run a UCSD virtual machine on top of that, though I would expect it to be slower than the microcoded version.

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But with PASCAL they revised the microcode soon after the Microengine came out
from what I read. Why? I don’t know. The WD chip set sounds generic, I wonder
why nobody seemed to use it.

The Terak used a PDP-11 instruction set, as implemented in the LSI-11. UCSD P-System II, the version just after UCSD P-System went commercial. Later versions of UCSD P-System ran on the Terak too, a matter of adapting the p-code interpreter.

The WD MicroEngine came much later. Adapted to p-code as instruction set. So no p-code interpreter, the UCSD compiler generated code that was executed directly by the MicroEngine.

The MicroEngine was a series of microcomputer products manufactured by Western Digital from 1979 through the mid-1980s, designed specifically to run the UCSD p-System efficiently. Compared to other microcomputers, which ran a machine language p-code interpreter, the Pascal Microengine had its interpreter implemented in microcode. So, p-code was, effectively, its native machine language.

The MicroEngine ran a special release III p-System, which was not to be used on any other platforms. However, the enhancements of release III were incorporated into release IV which was made publicly available for other platforms but not for the MicroEngine.

More info on my Pascal website UCSD P-System – Pascal for small machines ( A fascinating piece of history.