Ferranti Mercury - Meg

Meg

Another team, including the main designers of the Mark I, started with a design very similar to the Mark I but replacing valves used as diodes with solid state diodes. After watching use of the Mark I they also realized that the users of computers were almost all in the sciences, and they decided to add a floating point unit to greatly improve performance in this role. Additionally the machine was to run at 1 MHz, eight times faster than the Mark I's 125 kHz, leading to the use of the name megacycle machine, and eventually Meg.

Meg first ran in May 1954. The use of solid state diodes reduced valve count by well over half, reducing the power requirements an equal amount from the Mark I's 25 kW to the Meg's 12 kW. Like the Mark I, Meg was based on a 10-bit "short word", combining two to form a 20-bit address and four to make a 40-bit integer. This was a result of the physical properties of the Williams tubes, which were used to make eight B-lines, or in modern terminology, accumulator/index registers. Meg could multiply two integers in about 60 microseconds. The floating point unit used three words for a 30-bit mantissa, and another as a 10-bit exponent. It could add two FP numbers in about 180 microseconds, and multiply them in about 360 µsec.