Lavington, Simon (19 May 2011). Moving Targets: Elliott-Automation and the Dawn of the Computer Age in Britain, 1947 – 67. Springer Science & Business Media. p. 457. ISBN 9781848829336. 9781848829336
Campbell-Kelly, Martin (1989). ICL: a business and technical history. Table 11.4 English Electric System 4 announcements, 1965. For models 50 and 70: search for number 50. Clarendon Press. p. 243. ISBN 9780198539186. 9780198539186
ICL System 4 Usercode Digest, reference P000/5m/2.70/WM, about 1970
English Electric Computers, System 4-50 4-70 Usercode reference manual, Vol. 1, 14 February 1967.
English Electric Computers, System 4-50 4-70 Usercode reference manual, Vol. 2, 14 February 1967, Chapter 9.
English Electric Computers, System 4-50 4-70 Usercode reference manual, Vol. 2, 14 February 1967, Chapter 9.
English Electric Computers, System 4-50 4-70 Usercode reference manual, Vol. 1, 14 February 1967.
English Electric Computers, Hardware reference manual: Peripherals Vol 1, 1967.
English Electric Computers, Hardware reference manual: Peripherals Vol 1, 1967.
English Electric Computers, System 4-50 4-70 Usercode reference manual, Vol. 1, 14 February 1967.