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VAX, (Virtual Address Extension)
an instruction set architecture, developed by Digital Equipment Corporation (DEC) in the mid-1970s, to extend the PDP-11 architecture to a 32-bit orthogonal instruction set while adding a complete virtual memory system to the simple paging and memory protection of the PDP-11. The first computer to use a VAX CPU was the VAX-11/780, which DEC referred to as a Superminicomputer [1]. DEC's VAX strategy was formulated by Gordon Bell [2].
VAX 8350 [3]


VAX has 16 32-bit registers, R0-R15. R0-R11 general purpose, R12/AP the argument pointer, R13/FP the frame pointer, R14/SP the stack pointer, and R15/PC the program counter or instruction pointer.


The general form of a VAX instruction ...
opcode [ operand ] [ operand ] ...
... has each component being one byte, the opcode a value in the range 0 - 255, and each operand consisting of two nibbles, the upper 4 bits specifying an addressing mode, and the lower 4 bits (usually) a register number (R0 - R15).


The MicroVAX was a family of low-end minicomputers implemented the VAX instruction set architecture, first introduced in 1984.

Chess Programs

See also

External Links


  1. ^ Digital Equipment Corporation - VAX from Wikipedia
  2. ^ Beyond VAX: A Conversation with Gordon Bell. Computerworld, September 2, 1987, pdf from The Computer History Museum
  3. ^ DEC (Digital Equipment Corporation) VAX 8350 front view with cover removed, Photographer Adamantios, 2007, VAX from Wikipedia

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