August
1999 QUESTION 2 Total Marks: 20 Marks |
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| (a) | An instruction word has two components. Name
them, and explain the use of each.
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[2] |
| (b) | The length of an instruction word affects many
aspects of the system, both hardware and software. Briefly describe three of the effects
that varying instruction sizes have.
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[6] |
| Consider a set of
four processors P0, P1, P2, and P3, where Pi is an i-address machine. P0 is a zero-address
stack machine, while P1, P2, and P3 are conventional computers each with 16
general-purpose registers R0-R15 for data and address storage. All four processors have
instructions with the (assembly language) opcodes ADD, SUB, MUL, and DIV to implement the
operations +, - , * and / respectively.
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| (c) | Using as few instructions as you can, write a
program for each of the four machines to evaluate the following arithmetic expression :
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[8] |
| (d) | Assuming that the only instructions are those
which you have used, and that all addresses are 8 bits long, calculate the total
object-program size in bits for your programs for P1, Pr2, and P3. State any additional assumptions you make.
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[4] |