1. The Computer Architecture
VAX-11
The Computer Architecture

2. VAX-11 Timeline 1978 VAX-11/780 1980 VAX-11/750 1982 VAX-11/730
1984
VAX-11/725
VAX-11/785

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

4. 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
Fraction (second part): bit 16 is the least significant
Sign Bit
Exponent
Fraction (first part): bit 6 is the most significant

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]
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….
CISC machines – a trend thaniks to microprogramming. VAX architecture designed w/ ease of comilation in min – for example, mad a very general from of operan specification which all microinstructions would adhere to. The result worked beautifully, although the result was very complex instructions. This made it difficult to implement high powered applications. Furthermore, the relative slowness of microprograms led to its downfall. Here’s why:

9. Microinstruction Format
96 bits, 30 unique fields
You’re looking at the microinstruction format of the VAX-11 architecture. To spare you the tedious take of counding all those fields, we’ve pointed out that there are, in fact, 30 unique fields, collectively totalling a huge 96 bits, or 12 bytes, per instruction. In the interest of time, I’d like to only point out a few of the

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