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Manufacturer: Remington Rand
Year Design Started: Early 1947
Year First Shipped: March. 1951
Form Factor: mainframe
Word Size: 72 bits
Logic Type: vacuum tubes
Design Type: serial asynchronous
Clock Speed: 2.25 Mhz (basic - serial machine; add - 120 μsec for operation, 525 μsec for complete instruction)
Memory Speed: 400 μ sec (maximum)
Physical Address Size: 3 digits (decimal)
Predecessor(s): EDVAC
Successor(s): UNIVAC II
Price: US$1250-1500K (system)

The UNIVAC I ('UNIVersal Automatic Computer'; originally, just plain 'UNIVAC', until later models appeared) was the first commercially-available computer in the US.

It was a vacuum tube machine, using mercury delay lines for main memory, with 1000 words organized as 100 lines of 10 words each (to reduce access times). The CPU operated in digit-serial mode (i.e. a digit at a time), to match the memory. Its word size was 72 bits, with two instructions per word, with 12 digits/characters per word; it stored numbers with a form of packed decimal, with digits being represented as their character equivalents.

The only input/output devices were magnetic tape units, the 'UNISERVO'. Data could be tranferred to and from tape with offline peripherals which allowed use of printing, keyboard input, and punched cards.

A careful, slow power-on procedure, in which the filaments in the tubes were slowly warmed up, produced very reliable operation. (No doubt prior experience with tubes in the ENIAC had educated the UNIVAC's builders.)