page_title: IBM 700/7000 series
section_title: Decimal architecture (7070/7072/7074)
hierarchical_section_title: IBM 700/7000 series / Decimal architecture (7070/7072/7074)
caption_attribution_description: English: IBM 7070 (7074) Deutsch: IBM 7070 (7074) erster Transistorrechner von IBM
context_page_description: The IBM 700/7000 series is a series of large-scale computer systems that were made by IBM through the 1950s and early 1960s. The series includes several different, incompatible processor architectures. The 700s use vacuum-tube logic and were made obsolete by the introduction of the transistorized 7000s. The 7000s, in turn, were eventually replaced with System/360, which was announced in 1964. However the 360/65, the first 360 powerful enough to replace 7000s, did not become available until November 1965. Early problems with OS/360 and the high cost of converting software kept many 7000s in service for years afterward.
context_section_description: The IBM 7070, IBM 7072, and IBM 7074 are decimal, fixed-word-length machines. They use a ten-digit word like the smaller and older IBM 650, but are not instruction set compatible with the 650.
  Data format
  Word length – 10 decimal digits plus sign
  Digit encoding – two-out-of-five code
  Floating point – optional, with a two-digit exponent
  Three signs for each word – Plus, Minus, and Alpha
  Plus and Minus indicate 10-digit numeric values
  Alpha indicates five characters of text coded by pairs of digits. 61 = A, 91 = 1.
  Instruction format
  All instructions use one word
  Two-digit opcode (including sign, Plus or Minus only)
  Two-digit index register
  Two-digit field control – allows selecting sets of digits, shifting left or right
  Four-digit address
  Registers
  All registers use one word and can also be addressed as memory.
  Accumulators – three (addresses 9991, 9992, and 9993 – standard; 99991, 99992, and 99993 – extended 7074)
  Program register – one (address 9995 – standard; 99995 – extended 7074)
  Addressable from console only. Stores current instruction.
  Instruction counter – one (address 9999 – standard; 99999 – extended 7074)
  Addressable from console only
  Index registers – 99 (addresses 0001-0099)
  Memory
  5000 to 9990 words (standard)
  15000 to 30000 words (extended 7074)
  Access time – 6 microseconds (7070/7072), 4 microseconds (7074)
  Add time – 72 microseconds (7070), 12 microseconds (7072), 10 microseconds (7074)
  Input/output
  The 707x uses channels with a 7-bit interface. The 7070 and 7074 can be equipped with 7907 data channels to attach faster devices using a 9-bit interface.
caption: IBM 7074
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