Final Exam

IT320 Computer Architecture
Final Exam

Submit your detailed answers to the following questions to the Final Exam dropbox by
the due date. Do your own work and do not post anything regarding the exam for others
to see.

Question

1

The following Little Man program is supposed to input two numbers, compare them, and
output the higher of the two numbers.

Mailbox Mnemonic Code
01 IN 901
02 STO 90 390
03 IN 901
04 STO 91 391
05 SUB 90 290
06 BRP 10 810
07 LDA 91 591
08 OUT 902
09 COB 000
10 LDA 90 590
11 OUT 902
12 COB 000

What is wrong with this program, if anything? If necessary, modify the program so that it
produces the correct result.

Question 2

Write a Little Man Computer program that divides the number stored at location 50 by
the value 10. This can be done by subtracting 10 from the original number as many times
as possible and counting the number of times before the original value goes negative. For
example, dividing 86 by 10 will give the result of 8, because we can subtract 10 from 86
8 times before going negative (76, 66, 56, 46, 36, 26, 16, 6, -4). You may assume the
value 10 is already saved in location 51. Store the result in location 52.

Question 3

Suppose that the following instructions are found at the given locations in memory:

15 DAT 40

20 LDA 15
21 OUT

1

2

Show the contents of the IR, PC, MAR, MDR, and A registers at each step of the fetch-
execute cycle, for both instructions. Execution begins at address 20.

Question 4

(a) Suppose we are trying to determine the speed of a computer that executes the
Little Man instruction set. The Load and Store instructions each make up 12% of
the instructions in a typical program. Add, Sub, IN, and OUT take 8% each.
Branch instructions account for 44% of the remaining instructions. We can ignore
the COB instruction as it only executes once. Determine the average number of
instructions executed each second if the clock ticks at a speed of 250 MHz.

(b) Now imagine that the computer is pipelined. Estimate the number of instructions
that can be completed each second.

Question 5

A floppy disk rotates at a speed of 360 RPM. The disk is divided into 9 sectors per track
and there are 80 tracks. The disk is double sided. Each sector stores 512 bytes.
(a) What is the disk capacity in bytes?
(b) What is the minimum and maximum latency time for the disk?
(c) What is the transfer time for a single sector?

Question 6

A hard disk spins at a rate of 9600 RPM. Each cylinder (a track than spans all the
platters) contains 64 sectors on each platter surface.

(a) How much time does it take to read 16 consecutive sectors?
(b) If there are four platters and both sides of the platters are used and there are 1200

cylinders and each sector stores 512 bytes, what is the drive capacity?