In our last series, the Advent of Computers, we learnt about early computing, from the dawn of the Mesopotamian Era, to the 19th century. That brings us to the 20th century, where the age of electronic computing is just around the corner!
In the 20th century, the use of human systems was growing at an unprecedented rate, and life started getting more complex. Real-life problems could not be solved easily by just your average tabulating machine. More data had to be assimilated. Cupboard-sized electro-mechanical tabulating machines kept growing in size to accommodate more and more data. Yes, there were room-sized computers. One of the largest of these behemoths was the IBM ASCC (Automatic Sequence Control Calculator) Harvard Mark I, spanning about 15 metres in length!
Built in 1944 during the last part of WWII, the Harvard Mark I was the first of a series of electromechanical engines as a war effort by the US. It had over 760 000 parts, and over 804 kilometres of wire! Of course, such a large machine had to keep all its internal mechanics synchronized, which was why the Mark I – as it was called by the staff at Harvard University – had a 15-metre shaft running right through the machine driven by a five horsepower motor (about 4000 watts). One of the first programs to run on the Mark I was initiated on 29 March the same year by John von Neumann.
So how does this huge machine work? Well, the main logic behind this is ‘Mechanical Relays’.
Above is a circuit diagram of a relay. The bottom-most wire (the vertical one coming of the coil) is the ‘control wire’. When an electric current is passed through the control wire, the coil above is magnetised, attracting the switch, or metal arm, allowing current to pass through the wire to the other side. Simple, right? This controlled circuit can then be connected to many other components, like a counter, say, like in Hollerith’s machine which we discussed in the last post. Again, the problem with this was that the arm would take time to swing as it had mass. One might say, “Well, it’s just a millisecond! No big difference!” But what needs to be realised is that this relay, is just part of a much bigger machine, and the accumulation of such milliseconds can lead to great delays indeed, like in our behemoth Mark I. What was the solution?