How did CSIRAC work?

The Console consisted of two main parts:

Input Devices

The switch-panel was the only method by which simple programs or program data could be manually entered or modified in the main store. This process was difficult, as all information was entered in binary, using the rows of switches. Other functions available were disk write control and the speed control (Yes, even CSIRAC had a "Turbo" switch!).

Punched cards were originally used for program entry, but these proved to be too unreliable. 12-channel punched paper tape readers and punches were designed and built in the Radiophysics laboratory - these had the same number of rows as the punched cards. Later, 5 hole telegraphic paper tape equipment was also employed.

Output Devices

The CRT displays allowed the user to monitor the state of the machine. The A, B, C and H registers were available and could be constantly monitored during debugging . Any bank of sixteen words of the main store could be viewed in binary as well as the index registers. As a result, users had a primitive (16 x 20) bit mapped display on which cartoon characters were often displayed!

The console also had a modified ex-PMG Teletype for printing, and an old Rola speaker for reproduction of "music". The speaker's main purpose was for debugging. It was connected to the machine as an I/O device and instructions would be placed in the main program to produce "clicks" from the speaker. The operator would then know if the program had reached that part of the code successfully.

Programmers soon realised that CSIRAC could be instructed to play music, and experiments were soon implemented. These program tapes still survive and show that CSIRAC was probably the first computer to "play" music in the early 1950's.

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