F 1/6/06

HW due (for your own benefit): Please study your old tests. In case you have lost
track of your copies, blank versions of most of the problems are available
here.
Unit 0x00: Logical Building Blocks (9/20/05)
Unit 0x10: Bits, Bytes, Hex, and Hertz
(9/29/05)
Unit 0x20: What’s So Great About Digital?
(10/6/05)
Unit 0x30: Audio (10/20/05)
Unit 0x40: Compression (10/31/05)
Unit 0x50: Video (11/11/05)
Unit 0x60:Computation (12/1/05)
Units 0x70, 0x80, 0x90: Cryptography, Error
Correcting Codes, Information Theory (12/14/05)
Alternate Version of MultiUnit Test for
0x70, 0x80, 0x90 (12/16/05)


T 1/10/06

Midterm Exam, 11:00 a.m., Room S. The exam will last approximately 1 hour. If you
need more time, I will allow you to use the full 2hour time allotted.
The exam is cumulative. You may use your calculator, and the memory will not
be cleared. Therefore, if you wish to make notes in your calculator’s memory,
you may. However, I caution you that relatively few of the questions will be
of the simple “recall” type. I am more likely to ask questions that require
thought and may involve linking topics from multiple units. Here are some
sample questions:
1. Explain the relationship between bit
depth and the size of the color
palette that is possible. Give several examples.
2. Explain, in general terms, what RGB and YC_{b}C_{r} are (i.e.,
the vocabulary word) and why both systems are in common usage.
3. What vocabulary word refers to the effective information density of a data
file (i.e., information content in each byte, in each 64bit block, or in
some other suitable common measure)? Can the size of a ZIP file be used as a
rough indicator of this density? If not, how would you modify the ZIP file
size so that it could provide a good estimate?
4. A piece of graph paper is photographed. Ideally, we would expect to see
nothing but a grid of squares. However, suppose that the image shows a
mixture of squares and oddsized larger rectangles. How is this possible?
What vocabulary word(s) may apply to this situation?
5. Design an RLE protocol for encoding a 12 ´ 12 monochrome bitmap of your own choosing. Then
encode your bitmap in hex and calculate the compression ratio that you
achieved.
6. What mathematicians are remembered as (a) the author of the Incompleteness
Theorem, (b) the father of information theory, and (c) the greatest computer
scientist on the Enigma project? Give an additional sentence for each. For
example, state the Incompleteness Theorem in your own words.
7. Shannon’s
Theorem, which we unfortunately did not have time to discuss, gives a
maximum data rate (in bps) as a function of the available bandwidth of a
channel and the S/N ratio. Explain how this explains why your cell phone
loses fewer packets when you have a fresh battery (as opposed to an almost
dead battery), and why you may experience more “dead zones” during times of
the day when cell phone usage is at its peak. Try to use the word
“multiplexing” in your answer.
8. State Ohm’s Law and use it to calculate the maximum current (and from that, the maximum power) that a 12V
battery will deliver to a 10 KW resistive load. Is this enough to kill a person?
What if your hands are very salty or wet, and you touch the terminals of a
12V car battery?
9. DES, and especially tripleDES, are considered to be good ________
protocols. We say this because a 64bit key (actually _______ bits since
every 8th bit in the key is ignored) causes a _____________ of bits that is
so inscrutable that an adversary who does not have the key will have no
faster way to recover the original message than to perform a “________
________” search through about half of the ________ possible keys in the case
of DES, or ________ possible keys in the case of tripleDES.
10. Explain why ISBN and VIN check digits are calculated with weightings
instead of with simple parity checks.

