【Electrotechnical Laboratory】 ETL Mark II Relay-Based Automatic Computer

This was a large relay-based automatic computer developed by the Electrotechnical Laboratory based on the results of the ETL Mark I. Internally, it operated in 40-bit binary, with a 200 word memory capacity for data, using 22,253 relays and a completely asynchronous control system. The system performed self-checking of input and internal logic, and finished operation if check results were correct. The operating speed of the relays used in the ETL Mark II was an average of 10msec or higher -- which was slower than the average of 7msec for the USA's Harvard Mark II at that time -- but as a computer, it was 4 to 5 times faster. The system had a relay-based memory unit for 200 words, and could be expanded up to 1,000 words. The detailed design was done exclusively by researchers, and manufacturing was entrusted to Fuji Telecommunications Manufacturing (currently Fujitsu). The input unit tape reader and tape punch were fabricated by Shinko Seisakusho. The system was completed in November 1955, and was used for calculations within and outside the Electrotechnical Laboratory for about 10 years.

Today, the monitoring and control console of the ETL Mark II, and part of its main unit, are preserved in the National Science Museum, Tokyo.

ETL Mark II Operation ConsoleETL Mark II Relay Computer