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VAX-11

VAX-11. The Computer Architecture. VAX-11 Timeline. Floating-point representation. F_floating – (single precision) D_floating – (double precision) G_floating – (double precision, extended range) H_floating – (quad precision).

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VAX-11

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  1. VAX-11 The Computer Architecture

  2. VAX-11 Timeline

  3. Floating-point representation • F_floating – (single precision) • D_floating – (double precision) • G_floating – (double precision, extended range) • H_floating – (quad precision)

  4. VAX-11 Floating Point Representations: "F_Floating" Structure (32 bit "longword"): 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Fraction (first part): bit 6 is the most significant Fraction (second part): bit 16 is the least significant Sign Bit Exponent F_floating-point representation

  5. Language and the Machine • CISC machine • Large instruction set • Only 17 registers • 16 memory address modes • Little-endian machine

  6. Basic machine code • Starts with one or two byte op-code • Contains four bits to determine address mode • Followed by zero to five operand specifiers

  7. Register Mode • The one or two byte op-code is followed by (0101)2 • Those bits are followed by the four bit register address • Example: • [One or two byte op-code]01010000 • This code would actually be reversed when stored because it is a little-endian machine

  8. Microprogramming • Early implementation of microprogramming • Designed with ease of compilation in mind • Result was complex instructions • Difficult to implement high-performance applications • Downfall was slowness of microprograms • Here’s why….

  9. Microinstruction Format • 96 bits, 30 unique fields

  10. Conclusion • Superior system, for its time • Birth of the VUP • Technology eventually renders obsolete

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