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Computing at the IOA in the 1970s

Everyone at Cambridge University shared an IBM 370, which ran an operating system called Phoenix, because it arose from the ashes of OS360.  It crashed several times per day, so was roughly as reliable as Windows 3.1.  When I arrived at the IOA the machine had 2 megabytes of memory, accounting for Cloudy's small memory footprint to this very day. 

Time was allocated by giving everyone a certain number of shares in the computer.  I had a hundred shares.  The machine was very responsive if you did not use your shares, but if you used a lot of resources your priority would go down, and eventually you could do nothing at all.

The price of doing work on the machine depended on its load, being free if it was idle, but very expensive when it was heavily used.  So you had to work when the machine was least loaded.

The figure above shows the load on the machine for typical a day in 1979, and says everything anyone needs to know about life at Cambridge.  People wandered into work about 9:30AM, but by 10:30 it was time for coffee, which lasted until 11:30.  Then, at 1PM (not 12), it was time for lunch, which lasted about 1.5 hours.  After lunch everyone had an hour or so of intense activity, leading to tea at 4PM.  By 5:30 it was time to go home.  You can see a rebounding of efforts around 9PM as North Americans and Australians came back for another go.  (Cambridge motto: "If you are not good enough to get your work done between 9:30 and 5, you are not good enough to be here.")

My life was the mirror image of this figure - I came in to work as early as possible, stopping when the machine became expensive after 9:30 AM.  There would be two more periods of relatively cheap access at 11AM and 1PM, but then nothing could be done until after 6PM.  If I was lucky I could get three "shots" per day, meaning I could compile and execute Cloudy about three times per day.  And I got a reputation as being pretty anti-social ("you never come to coffee!").

Trying to use the computer early in the morning led to several encounters with the UK's infamous anti-vivisectionists.  I lived on Orchard Street, near City Centre, and passed the old Cavendish on the way to the Institute.  The Computing Centre was housed there, so I could get onto a terminal very early by going straight to the Cavendish, leaving for the Institute when the machine became too expensive around 9:30.  It turned out that the Biology Department was also in the old Cavendish, and a rumor had been started that they were cutting up small furry creatures.  A group of angry anti-vivisectionists began a protest and decided to stake out all exits from the Cavendish, starting around 9AM.  This went on for several months.  I had to get past them to get to the IoA, which led to angry words on many occasions ("why are you cutting up puppies?"), and getting hit with protest signs twice.  A few years after I left they set off a bomb in London that killed a three-year old child.

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Copyright 1978-2003 Gary J. Ferland