COMP S260

COMP S260 

Question 1

a)       Briefly describe the fetch-execute cycle.

b)       According to the format specified in Unit 2, write down the RTL steps for the SUB instruction of LMC and specify which part belongs to the fetch phase and which part belongs to the execute phase.

c)        Given the following LMC assembly program:

00 LDA 51;

01 ADD 52;

02 OUT;

03 COB;

51 DAT 22;

52 DAT 33;

Write the RTL statements for the first two assembly statements in the program and state the contents of PC, IR, ACC, MAR and MDR after executing each RTL statement.

d)       What is the purpose of including bit-shifting instruction?

e)       What are the disadvantages of having caching?

f)       A cache writing scheme can be defined in one of two ways. Write-through is the writes that can update both the cache block and the main memory. Write-back is that the writes can update just the cache block whereas the main memory is only updated when the block is replaced.

Write any two advantages and any two disadvantages of write-through.