NCR 315

NCR 315

The NCR 315 Data Processing System, released in January 1962 by NCR, [1] was a second-generation computer. All printed circuit boards used resistor-transistor logic to create the various logic elements. It used 12-bit slab memory structure using core memory. The instructions could use a memory slab as either two 6-bit alphanumeric characters or as three 4-bit BCD characters. Basic memory was 5k of hand-made core memory, which was expandable to a maximum of 40 k in four refrigerator-size cabinets. The main processor included three cabinets and a console section that housed the power supply, keyboard, output writer (an IBM Selectric-i typewriter), and a panel of lights that indicated the current status of the program counter, registers, arithmetic accumulator, and system errors. Input/Output was by direct parallel connections to each type of peripheral through a two-cable bundle with 1-inch-thick cables. Some devices like magnetic tape and the CRAM were daisy-chained to allow multiple drives to be connected.

Later models in this series include the 315-100 and the 315-RMC (Rod Memory Computer).


NCR 315-100

The NCR 315-100 was the second version of the original 315. It too had a 8 microsecond clock cycle, 10-40K Memory.

The primary difference between the older NCR 315 and the 315-100 was the inclusion of the Automatic Recovery Option (ARO). One of the problems with early generation of computers was that when a memory or program error occurred, the system would literally turn on a red light and halt. The normal recovery process was to copy all register and counter setting from the console light panel, and to restart the program that was running at the time of the error. Usually the restart was from the very beginning of the program.

The upgrade to the 315 required the removal of approximate 1800 wire-wrapped connection on the backplane, and the installation of approximately 2400 new point-to-point wired connection.


The NCR 315-RMC, released in July 1965, was the first commercially available computer to employ thin film memory. This reduced the clock cycle time to 800 nanoseconds. It also included floating-point logic to allow scientific calculations, while retaining the same instruction set as previous NCR 315 and NCR 315-100.

The thin film was wrapped around "rods" to allow faster reading and writing of memory.

Available languages

  • NCR Assembler Language
  • National Electronic Autocoding Technique (NEAT)
  • BEST

Available peripherals

  • NCR-321 Communications Controller
  • NCR-340 600-LPM line printer
  • Magnetic tapes
    • NCR-332 Magnetic tape drive (512 bpi)
    • NCR-333 Control Data CDC tape drive (512 bpi)
    • NCR-334 Magnetic Tape Drive (200/512 bpi)
  • NCR-353 Magnetic Card Random Access Memory (CRAM)
  • Card and tape equipment
    • NCR-361 Paper Tape Reader
    • NCR-371 Paper Tape Punch
    • NCR-376 IBM Card Reader/Punch
    • NCR-380 2000 CPS High speed card reader
    • NCR-472 Card Reader, Paper Tape Reader/Punch
  • NCR-??? Drum memory
  • NCR-402 MICR Check Reader/Sorter
  • NCR-420 Optical Character Reader(OCR)
  • NCR-407 High Speed MICR Check Reader/Sorter

See also