|Year Design Started:||Early 1947|
|Year First Shipped:||March. 1951|
|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)|
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.)