• The Power of Spin

    I was looking at my ipad recently and reflecting on the advances made since I started in I.T. Many people have written about the processing power in a digital phone versus the processing power available on Apollo 11 which took three men to the moon but I am interested in the mechanics behind bulk storage. My tablet has 8GB in a few square millimetres of silicon. My mainframes used to have great rolling disk drives with platters bigger than your barbecue.

    I remember an incident back in the 70s (that’s the 1970s) on a cold Sunday in Melbourne at the old Gas and Fuel Centre in Collins St. That was the pair of rectangular buildings you see above which have long been demolished and replaced by Federation Square. We were updating a Burroughs B7700 system to a B7800 system and this morning we were installing the processors. Each CPU was a cabinet about two metres tall, three metres long and sixty centimetres deep and weighed about a tonne. Today the equivalent would be about a square centimetre I.C.

    They were too big to come up the lift to the third floor so they had to be lifted by crane and come through a hole where some windows had been removed. Unfortunately, there are trams in Flinders St and as you can see from the photo taken a few kilometres away in St. Kilda, there is not much space between the overhead wires. These wires are at 600 volts DC and can carry enough power for a network of heavy trams so you don’t want to touch them with your jib. We had to negotiate with the city council to have the Flinders St trams shut down for two hours! We then powered off the entire computer room. (Almost an entire floor of the building on the right.)

    When the time came to power up the system, I started with the disk drives. Now I want you to forget the 500GB disk buried somewhere in your laptop or even the $200, 4TB external backup drive you may have picked up at Dick Smiths or Frys. These were subsystems consisting of a controller and eight disk cabinets. Each cabinet housed four disk platters on a common spindle rotating in a vertical plane. Each platter was about 6 – 8mm thick and about a metre in diameter and quite heavy. At speed each platter had hundreds of read/write heads pushed within nanometers of the surface by compressed air and they were sealed and pressurised through the most amazing set of filters. Each track had its own head hence the term “head per track” disk. The entire cabinet contained 5MB of storage. That’s not a misprint – that is FIVE MEGABYTES. That would hold maybe one photo from a high def smart phone camera today and it cost hundreds of thousands of dollars. Anyway, Gas and fuel had four complete subsystems. (32 disk cabinets)

    When you hit the ‘on’ button on a subsystem, the first disk drive would slowly begin to come up to speed. Given my marketing background and the title of this BLOG entry you probably expected a different type of spin eh? After about two minutes when the disk is nearly at maximum speed and the current draw is reduced it would automatically start the second disk in the string and so on. You can imagine that it takes a long time to get them all going. I decided to shortcut the process. I powered up each system as fast as I could walk between the controllers so that I had four coming up together. It would have made a good movie scene from Frankenstein’s lab as the deep throbbing noise and vibration began to shake everything. As the pitch started to rise there was a sudden thump and it all began to spin down. The lights flickered off and on and then the noise of the disks died away to be replaced by other distant sounds. I had dropped power to the entire building, all eleven floors. Lucky it was Sunday!

    Being a gas company, G & F had installed two gas turbines on the roof to supply backup power and they sprang into action although crawled might be a better description. They were spinning up almost as slowly as the disks but with much more drama. It sounded like a 737 landing on the roof. Being aware of the lag in starting gas turbines, they had also installed two diesel powered generators made by International Harvester. (Remember them?) These diesels were kept warmed by electric sump heaters and could literally spring into action reaching full revs in way less than one second. Not fast enough to avoid bedlam in the computer room but boy was it exciting. Being responsible for all this made it very, very exciting for a young technician like myself. It turned into an extremely long day but was quite a learning exercise with regard to electric power sources.

    Today, I can turn on my ipad and have it alive in a flash with more processing power and storage than the entire glass house we have been discussing. It runs all day on its internal battery with no moving parts and the trams are safe.

    Tell all this to the kids of today and they won’t believe you. (Monty Python)(needs Yorkshire accent)

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