The university's ICL 2960 was installed in 1976, and it moved to the EMAS
operating system in 1979. EMAS was very efficient, but as the years went
on the system was being stretched to its limits. By 1983 the system was
fully committed pretty well 24/7. Government policy meant that we wouldn't
get a replacement for another three years.

We knew we couldn't afford much of an upgrade, but we found out that there
was a spare ICL 2960 OCP [1] lying in a warehouse in Southall (I believe
it had been used for the recent Census). It was free to a good home (us)
but we had to pay about £350 for transport, etc. ICL kindly supplied the
extra bits we needed to hook it up, and by slightly reducing the
peripheral configuration (we no longer needed a card reader) we were
pretty well able to cover maintenance costs within budget.

The day came, and we IPLed the dual system for the first time. EMAS said
'Dual OCP found' and went to work. Basically, it worked until anything
went wrong, but it turned out that under exception conditions the
operating system was unable properly to control the second OCP (e.g. to
halt it). EMAS had never before been run on a dual 2960 OCP (there wasn't
one at Edinburgh), and it turned out that the instructions and image store
locations needed to communicate between OCPs were not standard across the
2900 range.

We asked ICL for documentation. No one knew where it could be found (we
assume), or perhaps someone decided we shouldn't have it. In any case, we
were stuck. Without documentation we couldn't modify the system supervisor
to make dual OCPs work as they should.

I had previously learned quite a bit about the ICL 2960 microcode, so I
retired once again to a darkened room with the microcode training manual,
and a microfiche reader. It took me about a day before I emerged, having
read a great deal of microcode and essentially reverse engineered all of
the image store locations and bit positions needed to do what we needed; I
think it was quite short. Armed with this, it was the work of minutes to
modify the supervisor, rebuild it and re-IPL.

The system worked very well for its final three years.

[1] Order Code Processor (CPU to most people)

--
Using UNIX since v6 (1975)...

Use the BIG mirror service in the UK:
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On Tue, 16 Apr 2024, Bob Eager wrote:

> The university's ICL 2960 was installed in 1976, and it moved to the EMAS
> operating system in 1979. EMAS was very efficient, but as the years went
> on the system was being stretched to its limits. By 1983 the system was
> fully committed pretty well 24/7. Government policy meant that we wouldn't
> get a replacement for another three years.
>
> We knew we couldn't afford much of an upgrade, but we found out that there
> was a spare ICL 2960 OCP [1] lying in a warehouse in Southall (I believe
> it had been used for the recent Census). It was free to a good home (us)
> but we had to pay about £350 for transport, etc. ICL kindly supplied the
> extra bits we needed to hook it up, and by slightly reducing the
> peripheral configuration (we no longer needed a card reader) we were
> pretty well able to cover maintenance costs within budget.
>
> The day came, and we IPLed the dual system for the first time. EMAS said
> 'Dual OCP found' and went to work. Basically, it worked until anything
> went wrong, but it turned out that under exception conditions the
> operating system was unable properly to control the second OCP (e.g. to
> halt it). EMAS had never before been run on a dual 2960 OCP (there wasn't
> one at Edinburgh), and it turned out that the instructions and image store
> locations needed to communicate between OCPs were not standard across the
> 2900 range.
>
> We asked ICL for documentation. No one knew where it could be found (we
> assume), or perhaps someone decided we shouldn't have it. In any case, we
> were stuck. Without documentation we couldn't modify the system supervisor
> to make dual OCPs work as they should.
>
> I had previously learned quite a bit about the ICL 2960 microcode, so I
> retired once again to a darkened room with the microcode training manual,
> and a microfiche reader. It took me about a day before I emerged, having
> read a great deal of microcode and essentially reverse engineered all of
> the image store locations and bit positions needed to do what we needed; I
> think it was quite short. Armed with this, it was the work of minutes to
> modify the supervisor, rebuild it and re-IPL.
>
> The system worked very well for its final three years.
>
> [1] Order Code Processor (CPU to most people)

Applause! They just don't make men like you any longer! ;) The only thing
even _remotely_ close was when I was young and modified my UFO: Enemy
unknown game together with an acquaintance to make it 2 player game in
tactical mode so we could play against each other over the internet.

Extremely hacky and not very elegant, but it worked and we did have fun
playing humans vs aliens against each other. =)

On 2024-04-16, Bob Eager <news0009@eager.cx> wrote:
> I had previously learned quite a bit about the ICL 2960 microcode, so I
> retired once again to a darkened room with the microcode training manual,
> and a microfiche reader. It took me about a day before I emerged, having
> read a great deal of microcode and essentially reverse engineered all of
> the image store locations and bit positions needed to do what we needed; I
> think it was quite short. Armed with this, it was the work of minutes to
> modify the supervisor, rebuild it and re-IPL.
>
> The system worked very well for its final three years.
>
> [1] Order Code Processor (CPU to most people)

*applause* I am thoroughly enjoying your war stories.

Encore!