Ferranti Mercury

The Mercury was an early commercial computer from the mid 1950s built by Ferranti. It was the successor to the Ferranti Mark 1, adding a floating point unit for improved performance, and increased reliability by replacing the Williams tube memory with core memory and using more solid state components. The computer had roughly 2000 vacuum tubes (mostly type CV2179/A2134 pentodes, EL81 pentodes and CV2493/ECC88 double triodes) and 2000 germanium diodes. Nineteen Mercuries were sold before Ferranti moved on to newer designs.

When the Mark I started running in 1951, reliability was poor. The primary concern was the drum memory system, which broke down all the time. Additionally, the machine used 4,200 thermionic valves, mostly EF50 pentodes and diodes that had to be replaced constantly. The Williams tubes, used as random access memory and registers, were reliable but required constant maintenance. As soon as the system went into operation, teams started looking at solutions to these problems.

One team decided to produce a much smaller and more cost-effective system built entirely with transistors. It first ran in November 1953 and is believed to be the first entirely transistor-based computer. Metropolitan-Vickers later built this commercially as the Metrovick 950, delivering seven.

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. At that time computers were used almost always 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.

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