UNIVAC LARC

The UNIVAC LARC, short for the Livermore Advanced Research Computer, is a mainframe computer designed to a requirement published by Edward Teller in order to run hydrodynamic simulations for nuclear weapon design.

Two LARC machines were built, the first delivered to Livermore in June 1960, and the second to the Navy's David Taylor Model Basin.

It used bi-quinary coded decimal arithmetic with five bits per digit (see below), allowing for 11-digit signed numbers.

The Processor is an independent CPU (with a different instruction set from the Computers) and provides control for 12 to 24 magnetic drum storage units, four to forty UNISERVO II tape drives, two electronic page recorders (a 35mm film camera facing a cathode-ray tube), one or two high-speed printers, and a high-speed punched card reader.

The data transfer bus connecting the two Computers and the Processor to the core memory was multiplexed to maximize throughput; every 4-microsecond bus cycle was divided into eight 500-nanosecond time slots: The core memory system enforces a system of interlocks and priorities to avoid simultaneous access of the same memory bank by multiple sections of the system (the Computers, Processor, and I/O DMA Synchronizers) without conflicts or deadlocks.

If another section attempts to address the same memory bank during this time, it is locked out and must wait, then try again in the next 4-microsecond cycle.

In the basic five-bit biquinary code of the UNIVAC-LARC, 15 combinations are allowed, any one of which may be stored in any digit position in storage.