KDF9

Computer English Electric KDF 9 
Manufactured by English Electric Computers
English Electric Leo Marconi Computers
Owned by  English Electric Ltd - Stafford
Dates Worked 1968 
   At the end of 1967 I got restless again and I joined English Electric in Stafford as part of a team to plan for a new computer system (see System 4) to replace their KDF9. The first thing I did was to be trained on the KDF9 at the English Electric Computers site at Kidsgrove (north of Stoke). However I would never program it for real.
Programming  KDF9 assembler was a strange language( "The KDF9 is remarkable because it is believed to have been the first zero-address instruction format computer to have been announced (in 1960). It was first delivered at about the same time (early 1963) as the other famous zero-address computer, the Burroughs B5000 in America. Like many modern pocket calculators, a zero-address machine allows the use of Reverse Polish arithmetic; this offers certain advantages to compiler writers"). It used a 16 entry stack and all operations were performed on the top element. To add locations A and B and put the answer in C the commands were " A , B, +, =C ". A quick way to decrement the top entry was " NEG, NOT " which changed the sign and then reversed the bits. "NOT, NEG" incremented.
The unforgivable programming sin was not to control the stack properly resulting in "stack overflow"  or "stack underflow".
Hardware
 The KDF9 like the LEO III was a fully transistorised computer with core store and used M/T as the main storage media. Input was usually paper tape. Some systems used large fixed disks or drums for random access. 'Large' here is physical (1 ton) rather than storage capacity(24Mb).
Software The KDF9 was primarily a scientific rather than a commercial system - a number of early FORTRAN and ALGOL compilers were written for it. The Stafford machine was used for both types of computing. Universities developed their own versions of the operating system.
   Paper Tape Reader
Paper Tape Reader

A 24Mb fixed disk
24Mb Fixed Disk
KDF9 Computer Room
KDF9 Computer Room
 Above - photos from Eric Foxley's site
Below - Newcastle University KDF9

KDF9 at Newcastle
Newcastle University
Links Origins of KDF9  (and Leo III)

The English Electric KDF9 Computer

Eric Foxley - Misc Computing

Computer Conservation Society    -includes list of Installations

Birmingham University - KDF9 with Disk
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