Editing ENIAC (section)

===Reliability===
ENIAC used common [[Octal tube|octal-base]] [[radio tube]]s of the day; the decimal [[accumulator (computing)|accumulators]] were made of [[6SN7]] [[flip-flop (electronics)|flip-flops]], while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions.<ref>{{Harvnb|Burks|1947|pp=756–767}}</ref> Numerous [[6L6]]s and [[6V6]]s served as line drivers to drive pulses through cables between rack assemblies.

Several tubes burned out almost every day, leaving ENIAC nonfunctional about half the time. Special high-reliability tubes were not available until 1948. Most of these failures, however, occurred during the warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress. Engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. According to an interview in 1989 with Eckert, "We had a tube fail about every two days and we could locate the problem within 15 minutes."<ref>{{cite web |url=http://www.computerworld.com/s/article/108568/Q_A_A_lost_interview_with_ENIAC_co_inventor_J._Presper_Eckert |title=A lost interview with ENIAC co-inventor J. Presper Eckert |first=((Alexander 5th)) |last=Randall|publisher=Computer World |date=2006-02-14 |access-date=2015-03-29}}</ref>
In 1954, the longest continuous period of operation without a failure was 116 hours—close to five days.