HW5
Chapter 5 Exercise 1, 2, 4, 7, 12, 15, and 19
(Handin Date: 2013/11/18)
1. What are the advantages and disadvantages of using a very large
memory cell size, say, 𝑊 = 64 instead of the standard size
𝑊 = 8? If each integer occupies one 64-bit memory cell and is
stored using sign/magnitude notation, what are the largest
positive and negative integers that can be stored? What if two
cells are used to store integers?
2. At a minimum, how many bits are needed in the MAR with each
of the following memory sizes?
a) 1 million bytes
b) 1 billion bytes
4. Explain what use a read-only memory (ROM) serves in the
design of a computer system. What type of information is kept
in a ROM, and how does that information originally get into the
memory?
Ans: Read-only memory can be used to store essential system
instructions that users cannot overwrite. The information
could originally be stored in the ROM by hardwiring the
electronic circuitry.
7. Assume that our MAR contains 20 bits, enabling us to access up
to 220 memory cells, which is 1 MB, but out computer has 4
MB of memory. Explain how it might be possible to address all 4
MB memory cells using a MAR that contain only 20 bits?
12. Assume that a floppy disk has the following characteristics:
Rotation speed=7200 rev/min
Arm movement time=0.5 msec (fixed starting time) + 0.05
msec (for each track crossed). Assume on average the disk
arm must move 150 tracks.
Number of surfaces=2 (This is a double sided disk. A single
read/write arm holds both read/write heads.)
Number of tracks per surface=500
Number of sectors per track=20
Number of characters per sector=1024
a) How many characters can be stored on this disk?
b) What are the best-case, worst-case, and average-case
access times for this disk?
15. Assume that our disk unit has one read/write head per track instead
of only one per surface. (A head-per-track disk is sometimes referred
to as a drum.) Using the specifications given in Exercise 12, what are
the best-case, worst0-case, and average0case access times>? How
much have the additional read/write heads helped reduce access
times (% of reduction)?
19. Consider the following structure of the instructions register.
OP Code
6 bits
Address-1 Address-2
18 bits
18 bits
a) What is the maximum number of distinct operations codes that
can be recognized and executed by the processor on this
machine?
b) What is the maximum memory size on this machine?
c) How many bytes are required for each operation?