Example Exam Problems
1. (25 pts) Execute the following MIPS code fragment, showing the status of the register
file and memory when execution is completed. Use hexadecimal to show the values.
add $13,$0,$0
L1: addi $13,$13,0x04
lw $11,0x1C($13)
add $14,$11,$10
sw $14,0x20($13)
bne $12,$13,L1
BEFORE
Registers Memory
Address Value Address Value
$10 0x10 0x020 0x22
$11 0x14 0x024 0x30
$12 0x08 0x028 0x40
$13 0x28 0x02C 0x50
$14 0x1234 0x030 0x60
AFTER
Registers Memory
Address Value Address Value
$10 0x10 0x020 0x22
$11 0x32 0x024 0x32
$12 0x08 0x028 0x42
$13 0x08 0x02C 0x50
$14 0x42 0x030 0x60
2. (20 pts) You wish to speed up a 1 GHz machine that spends 80% of its clock cycles
on arithmetic instructions, 10% on load/store, and 10% on branch/jump. Given your
budget, you have two choices. You can increase the overall clock rate to 1.1 GHz, or
you can add branch prediction logic and an improved cache to reduce the
branch/jump and load/store times to half their original values. Which will result in a
faster machine? Why?
1.1 GHz will cause a speedup of 1.1x
The improved logic will cause the time to decrease from 100
units to 80 + 10/2 + 10/2 = 90, so the speedup is 100/90 =
1.11x, so this is better.
