floating point (A + B) + C is not necessarily the same as A + (B + C) i.e. the + operation is not associative.) Before long, however, it was recognized that error rates with transistor machines was not an issue; they either worked correctly or didn’t work at all. Consequently, the idea of sum checks was abandoned. The initial matrix package proved a very useful system testing tool as it was able to generate lengthy performance checks well before more formal test packages which were subsequently developed. There is a legend that the KDF9 was developed as project KD9 (Kidsgrove Development 9) and that the 'F' in its designation was contributed by the then Chairman after a long and tedious discussion on what to name the machine at launch—"I don’t care if you call it the F—". The truth is more mundane: the name was chosen essentially at random by a marketing manager. (See also KDF8 for the parallel development and use of a commercially oriented computer.) The EGDON operating system was so named because one was going to UKAEA Winfrith: in Thomas Hardy's book The Return of the Native Winfrith Heath is called Egdon Heath. EGDON Fortran was called EGTRAN. Eldon was so named because Leeds University's computer was located in a converted Eldon chapel. Physical The machine weighed more than . Control desk with interruption typewriter 300 lb (136 kg), main store and input/output control unit 3,500 (1,587 kg), arithmetic and main control unit 3,500 (1,587 kg), power supply unit 3,000 (1,360 kg). See also Reverse Polish notation (RPN) Notes References External links The English Electric KDF9 The Hardware of the KDF9 The Software of the KDF9 The KDF9 and Benchmarking The KDF9: a Bibliography The KDF9 character codes ee9, a KDF9 emulator written in GNU Ada Delivery List and applications for the English Electric KDF9 History of KDF9 Algol compiler The Whetstone KDF9 Algol Translator Some KDF9 Algol compiler anecdotes Presentation on KDF9 Algol on visit from Dijkstra KDF9 Nest (images) Source Code for KDF9 port of Atlas Autocode compiler Early British computers KDF9 Magnetic logic computers Transistorized computers KDF9 Computer-related introductions in 1964