Manchester Mark I

Note: This article is about the early British computer. Manchester Mk1 can also refer to the Avro Manchester heavy bomber in RAF service during the early stages of World War II.

The Manchester Mark I was one of the earliest electronic computers, built at the University of Manchester in England, in 1949. It was developed from the Small-Scale Experimental Machine or "Baby". It is especially historically significant due to its pioneering inclusion of a kind of index registers in its architecture.

In its final specification from October 1949 the Mark I stored data in one 40-bit number (the accumulator) or two 20-bit instruction registers, and had two 20-bit address modifier registers, called "B-lines", which could function either as index registers or as so-called base address registers. This is the earliest known implementation of such index/base registers – an important innovation in computer architecture, unknown in other machines until the emergence of second-generation computers (approximately 1955–1964).

The Mark I could perform 40-bit serial arithmetic, with hardware add, subtract and multiply and logical instructions. It used a single-address format order code with thirty function codes. Standard instruction time was 1.8 milliseconds, but multiplication was much slower.

For memory the Mark I used two Williams tubes, each storing 64 rows of 40 points, for a total of 128 words. 64 words was considered to be a single "page", so the system stored 4 pages. In addition to the tubes were two magnetic drums, which could store 64 pages (32 tracks) each. Instructions were loaded into the machine by using paper tape.

External links

• The Manchester Mark 1 (http://www.computer50.org/mark1/MM1.html)