Computer LEO III (13)
Manufactured by Leo Computers Ltd
English Electric Leo Marconi Computers Ltd
ICL (5 machines for Post Office in 1969)
Owned by British Oxygen, Worsley, Manchester
Dates Worked 1962-65
  I was originally employed by Cerebos Salt in Willesden, London. I was loaned to the British Oxygen team as the Cerebos machine was not ready. A desire to move north combined with youthful arrogance resulted in my resigning from Cerebos and joining BOC. I started at Worsley in August 1963 (having just got married).

I was employed as Junior Programmer at £700 pa eventually dropping the 'Junior'. The initial application was Sales Analysis, invoice data was punched into paper tape by an army of girls and then verified by retyping the same data (discrepancies stopped the machine, the data was visually checked and, if needed,  corrections made).

Programming We used an assembler code with numeric addressing (Section and sub-section (? forgotten details). Operation codes were numeric 00-load word 01-add word etc. (Virtually) all processing took place in in a single (double word) register .
The program was punched onto P/T (paper tape) compiled and stored on M/T (magnetic tape). As far as I remember any standard routines were added (as P/T prior to compilation. All I/O (including tape buffering) had to be included in the program.
Compilation took place overnight and any syntax errors were not forgiven. Code was checked and double checked by another programmer prior to submission. If a test failed you got a 'core dump' (in hexadecimal) with any output. That was when the work got really interesting.
Hardware The LEO III comprised about 30  6 foot cabinets containing circuit boards,(Ampex?), Magnetic tape units (8) etc. (Analex ?) Line printers (1200lpm). Paper tape readers and a large console with lights. (not as many as the EE KDF8(?) console which starred in many films and TV programs where a 'computer' was required. It had rows of illuminated switches that the operator could play like an organ).

One feature that was was unusual (if not unique) was the ability to do arithmetic in different bases, not just decimal or binary(hexadecimal) but in Pounds,shillings and pence (£.s.d) or pounds and ounces. This was achieved by having an 'excess digits'(?) register containing a constant that was added/subtracted(if no carry) to each word before/after 'hex' arithmetic was carried out. For example decimal arithmetic used '66666' so that 9+1(+6) = '10' (hex). '£sd'  used  '6614 6 4' (I think?) to provide for  pence (1 digit 0-11), shillings (two digits 0-19). At that time the usage of A-F for 10 to 15 was not known and we used character such as '£', '#', for 12 to 15 ( there were special '10' and '11' characters to hold 'old pence').
Software The LEO III had one of the earliest multi-programming operating systems, up to 3 jobs could run simultaneously. Printing was usually spooled so that one of those jobs kept the printer busy.
  LEO III at LyonsA LEO III at J Lyons    LEO II at Colonial Life - MelbourneColonial Mutual Life Melbourne
  Photos from LEO Computer Society Web Site

LEO Computers Society - dedicated to keeping the memory fresh

Computer Conservation Society - includes list of installations

Book - A COMPUTER CALLED LEO: Lyons Tea Shops and the world’s first office computer by Georgina Ferry 
Staffs University Computing Futures Museum   - Leo Page
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