31-bit computing

In computer architecture, 31-bit integers, memory addresses, or other data units are those that are 31 bits wide.

In 1983, IBM introduced 31-bit addressing in the System/370-XA mainframe architecture as an upgrade to the 24-bit physical and virtual,[1] and transitional 24-bit-virtual/26-bit physical,[2][3] addressing in System/370.[4][5] This enhancement allowed address spaces to be 128 times larger, permitting programs to address memory above 16 MB (referred to as "above the line").[6][1] Support for COBOL, FORTRAN and later on Linux/390 were included.

In the early 1980s, the Motorola 68012 was introduced; it had 32-bit data and address registers, as the Motorola 68010 did, but instead of providing the lower 24 bits of an address on the address pins, it provided all but bit 30 on the address pins.[7]

  1. ^ a b "A brief history of virtual storage and 64-bit addressability". IBM.
  2. ^ "with transitional support for 26-bit"
  3. ^ KE Plambeck (2002). "Development and attributes of z/Architecture"" (PDF).
  4. ^ Robert T. Fertig (May 1983). "XA: The View From The Trenches (pp.122-136)". Datamation.
  5. ^ Ronald L. Bond (May 1983). "XA: The View From White Plains (pp.139–152)". Datamation.
  6. ^ "...to run in the 31-bit area above the line,... "Rewriting to run in 31 bit area". Computerworld. October 27, 1986. p. 13.
  7. ^ "4.1 SIGNAL DESCRIPTION" (PDF). MC68010/MC68012 16-/32-Bit Virtual Memory Microprocessors (PDF). Motorola Semiconductor. May 1985. pp. 4-1–4-2. ADI942R2. {{cite book}}: |work= ignored (help)

31-bit computing

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