1956 · Transistorized Computer Modules · Work 829 of 1,871
A computer room of 1956 in a university laboratory in Massachusetts, a wall of cream-white plug-in frames, each densely set with upright grey plug-in tubes eight millimetres thick with coloured caps in blue, yellow, orange, white and green, a hand in a rolled-up white shirt sleeve pulling out a single tube with a yellow cap, in front a console with a round screen showing a scattered pattern of bright green dots, a light pen on a coiled cable lying before it, fluorescent light from above, a linoleum floor.
What it was used for
The bottles were the plug-in units of the logic of the TX-0, which MIT's Lincoln Laboratory built in 1956; the machine became operational in April 1956. The 1974 operating history names 2 purposes: to test and evaluate the use of transistor circuitry as the logical elements in a high-speed computer, and to provide means for testing a large capacity 65,536-word magnetic-core memory. Except for the flip-flop module, the transistors were packaged one, two or three to a plastic plug-in bottle screwed onto a socket; the Computer History Museum describes a five-pin socket with 1 transistor and 2 resistors soldered to it and a clear bottle over them, and in a second version a seven-pin socket with 2 transistors, 2 resistors and 1 capacitor. A dozen different module types were used.
What was new
The TX-0 had about 3,600 transistors, ran at 5 MHz and, per the operating history, managed better than 80,000 additions per second; the flip-flop module alone used 10 transistors. The logic was fully transistorised, with tubes left only in timing and memory - 100 vacuum tubes for the timing pulses, 425 dual triodes alongside 625 transistors in the memory system. The L-5122 types used came from Philco's research division and were not yet catalogue parts; they were later sold as the 2N240. Their durability was tested too: after 6,000 hours of operation 800 transistors were removed and retested, the most serious change being a slight decrease in current gain, and after 10,000 hours again. The memory whose testing was one of the two reasons for building the machine was transferred to the TX-2 in the spring of 1958; on 1 July 1958 the TX-0 was shut down for its move to the MIT campus in Cambridge, where it was installed by the end of the month.
What the sources leave open: The attribution of the title rests on the Computer History Museum catalogue, which lists two objects as TX-0 Transistor plug in bottle modules, dated circa 1956. No source gives the number of bottles fitted or a price or rental; the catalogue weight of 1 lb is the same for 2 as for 55 modules. The operating history contradicts itself on the date of the later move to the museum: 1975 in the conclusion, 1976 in the abstract. Other candidates for 1956 were not examined.