VAX-11
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Transcript of VAX-11
VAX-11
The Computer Architecture
VAX-11 Timeline
1978 VAX-11/780
1980 VAX-11/750
1982 VAX-11/730
1982 VAX-11/782
1984 VAX-11/725
1984 VAX-11/785
Floating-point representation
• F_floating – (single precision)
• D_floating – (double precision)
• G_floating – (double precision, extended range)
• H_floating – (quad precision)
F_floating-point representation
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 (second part): bit 16 is the least significantSign Bit
Exponent Fraction (first part): bit 6 is the most significant
Language and the Machine
• CISC machine
• Large instruction set
• Only 17 registers
• 16 memory address modes
• Little-endian machine
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
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
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….
Microinstruction Format
• 96 bits, 30 unique fields
15 13 12 0
VAK FEK SCK
31 30 29 26 25 24 23 22 20 19 18 17 16
ADS FS
47 46 43 42 41 35 34 32
63 58 57 55 54 51 50 48
RMX
79 78 77 76 72 71 70 69 66 65 64
95 92 91 88 87 85 84 82 81 80
AMX
ACF
IBC DK SHF BMX
DT BEN ALU SUB
MCT/CID SPO PCK
KMX SI/ACM QK SGN
EALU JMP
IEK MSC CCK EBMX SMX
Conclusion
• Superior system, for its time• Birth of the VUP• Technology eventually renders
obsolete