Happy Birthday VAX 11/780

Roger Holmes roger.holmes at microspot.co.uk
Tue Oct 26 03:48:58 CDT 2010

From: William Donzelli <wdonzelli at gmail.com>
>> There was talk of the VAX design being the inspiration for the Motorola 68k. Isn't it more likely that the PDP11 influenced the design of both the VAX and the 68k?
> Big microcoded CISC was the dominant thinking in computer architecture
> at the time, so it is really hard to say that X influenced Y.

>> The engineers did not believe the Motorola design was practical and we worried about a large 64 pin chip in the environment of a military helicopter's avionics bay (G forces, vibration, expansion, cooling etc) and it was decided to go with the 48pin Zilog Z8001 instead.
> Why not use PGA or Flatpack?

For production the plan was for bare silicon mounted on hybrids but the silicon itself was large. Of course as production progressed die sizes would have been shrunk but not fast enough.

We also used up to 22 layer PCBs!  IIRC, samples when they became available would have been DIPs, they were for the Z8001 for sure. We used our own Elliott 920ATC computers to load code into shared RAM before the microprocessor was released from reset. I also wrote a simulator (for the Z8001) for compiler, high level assembler and other utility software development.

Unfortunately working at a technical level on the leading edge does not pay very well in the UK. I was told I would not be able to progress to a higher grade without becoming a manager, so I left and became a major shareholder and director of a tiny company and have remained technical to this day. Somewhat to my surprise I found I can still out-program every other programmer we have ever employed despite now being 57 years old.

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