Editing EDSAC (section)

===Physical components===
[[File:EDSAC (5).jpg|thumb|9-inch tubes used for monitoring]]
[[File:EDSAC (20).jpg|thumb|William Renwick with 5-hole tape reader and Creed teleprinter]]
As soon as EDSAC was operational, it began serving the university's research needs. It used [[delay-line memory|mercury delay lines]] for memory and [[derating|derated]] [[vacuum tube]]s for logic. Power consumption was 11&nbsp;[[Kilowatt|kW]] of electricity.<ref>{{cite web| url=https://www.youtube.com/watch?v=lXJ-tYqPARg | title=EDSAC Simulator | publisher=Computerphile | work=[[YouTube]] | date=21 February 2018 }}</ref><ref name="autogeneratedcl" /> Cycle time was 1.5&nbsp;ms for all ordinary instructions, 6&nbsp;ms for multiplication. Input was via five-hole [[punched tape]], and output was via a [[teleprinter]].

Initially, registers were limited to an [[Accumulator (computing)|accumulator]] and a multiplier register. In 1953, [[David Wheeler (computer scientist)|David Wheeler]], returning from a stay at the [[University of Illinois at Urbana–Champaign|University of Illinois]], designed an [[index register]] as an extension to the original EDSAC hardware.

A magnetic-tape drive was added in 1952 but never worked sufficiently well to be of real use.<ref name="autogeneratedcl">{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/statistics.html | title=Some EDSAC statistics | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref>

Until 1952, the available main memory (instructions and data) was only 512 18-bit words, and there was no backing store.<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%201%20applications | title=EDSAC 1 applications | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref> The delay lines (or "tanks") were arranged in two batteries providing 512 words each. The second battery came into operation in 1952.<ref name="autogeneratedcl"/>

The full 1024-word delay-line store was not available until 1955 or early 1956,<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%201%20maintenance | title=EDSAC 1 maintenance | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref> limiting programs to about 800 words until then.

John Lindley (diploma student 1958–1959) mentioned "the incredible difficulty we had ever to produce a single correct piece of paper tape with the crude and unreliable home-made punching, printing and verifying gear available in the late 50s".<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%202%20operating | title=EDSAC 1 operating | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref>