|
MODD / Mr. Hansen |
Name:
_____________________________ |
|
10/14/2013 |
Start
time: ______ End time: ______ |
Practice Test
Note: Most of these problems are straightforward. In
fact, many are recycled from the Big Quiz that you took on September 20. However,
it is usually the case (and this week’s test is no exception!) that at least
one or two test problems will force you to think really, really hard, and you
may not even be able to solve them completely. That’s simply because STA is a
rigorous school, and you’re all capable young men who need to be challenged. Do
your best. Please record your overall time above, as well as the elapsed time
for each problem that you were unable to solve quickly.
1. Write the ASCII contents in hex (using proper prefix or suffix notation, not
both) for a text file that has the contents
Binary#!
followed by a beep and the end-of-file indicator (Ctrl+Z
or decimal value 26). Important: Give
answer in little-endian byte order.
2. How
many gigabytes are in a zettabyte? Give answer as a
power of 2 (exact) as well as a power of 10 (approximate).
3. A DSL
modem with a download speed of 500 mbps (500 megabits per second) is used to
transfer 10 MP3 files, each of size 4.5 MB. Estimate the total download time
required, and show your work. Cryptic, missing, or unclear work will not earn
full credit even if your answer is correct.
4. The
30-year-old laptop computer in Mr. Hansen’s classroom has an operating system
stored on a 32 KB ROM chip. The Windows 7 operating system on Mr. Hansen’s
relatively modern laptop computer has a total installed size of approximately
18 GB. Approximately how many times larger is the Windows operating system?
Show your work. Cryptic, missing, or unclear work will not earn full credit,
even if your answer is correct.
5. How many cycles per second
is 2400 THz? Note: Cycles per second
do not use powers of 2. Therefore, your answer should end in zeros. Commas are
required, but no work is expected.
6. In a signed qword format,
how can you tell that 0x8FFFFFFFFFFFFAA9 denotes a negative integer?
______________________________________________________
What base-10 integer is represented by 0x8FFFFFFFFFFFFAA9? ____________ Show
all work below. Be clear, and write neatly! Minor errors will be forgiven.
7. For the qword value given in #6, give (in both decimal and hex) the
integer that is 1 greater.
Decimal answer: ______________________
Hex answer in qword format: ______________________
8. Complete the thought: Computers never
actually “subtract” one value Y from another value X; instead, “X minus Y” is
accomplished by ___________ ___________ ___________ ___________ ___________
___________ ___________ ___________ . Correct spelling is required for full
credit.
9. What format is 0x0001C58D
in: byte, word, dword, or qword?
__________________________
Convert 0x0001C58D to binary: __________________________________________
Convert 0x0001C58D to decimal, showing all work below and then using your
calculator to get a final answer as an integer.
10. (a) In decimal, perform
the arithmetic operation –55 – 174. (This is easy. No work required, just give
the answer.) Answer: __________
(b) Now let’s encode –55 and –174 as signed word values in hex. We’ll do the
first one for you: –55 = 0xFFC9. Now it’s your turn: –174 = 0x__________ . Show
your work below if you desire partial credit in the event of a mistake.
(c) Add the hex value 0xFFC9, in signed word format, to your answer from part
(b). Answer: 0x__________ . Show your work below if you desire partial credit
in the event of a mistake.
(d) Convert your answer in part (c) back into decimal (base 10). Show your work
below (required). If you do
this correctly, your answer should match the answer you obtained in part (a).
11. Fill in each blank with
the word or phrase that best fits.
ASCII is being replaced, more
and more, by ___________ , which uses _________ bits per character and is
therefore a “_________ -byte” character code.
A byte equals _______ bits or
_________ hex digits.
The total number of different
possible keys that could be created using 1024 bits is ____________________ as
a power of 2, or about _________________ as a power of 10.
Convert the Unicode stream
0x004D006F00440064 into text, being careful to distinguish upper and lower
case: ______________
12. Fill in each blank with
the word or phrase that best fits.
An SSD is _________ and more
reliable than a conventional mechanical hard disk drive. The reliability
improvement with an SSD is due to the lack of moving _______ , which means that
a head _________ cannot occur.
Here is an apparently random bitstream:
110000011101101010101100000110101110000101000011111000110110001000011011010110010101001101001010100111110001100101111110
Translated into ASCII (big-endian byte order), the message is gibberish: ÁÚ¬áCãbYSJŸ~
However, if you take bits 5, 10, 15, 20, and so on from the original bitstream, you can assemble 3 bytes of ASCII code and can
recover a secret English word. All 3 letters are in lower case. Show your
scratch work below:
Write the secret word here: _______
What term do we use for a situation like this, in which information is “hidden
in plain sight” without really being encrypted? __________________
13. A 6-spoke wheel is
spinning at 600 rpm (i.e., 10 revolutions per second). That means that 60
spokes per second are passing the “12 o’clock” position at the top of the
wheel.
(a) If a TV-style video file (30 fps) is created, at what frequency will the
wheel appear to be spinning? Give answer in revolutions per second.
(b) If a motion picture (24
fps) is made of the spinning wheel, at what frequency will the wheel appear to
be spinning? Give answer in revolutions per second.
(c) Explain why someone viewing the motion picture (24 fps) will be unable to
tell whether the wheel is rotating forward or backward.
14. We are going to take a
secret 4-byte message, FLAN, and we are going to XOR-encrypt it with the key
STA1.
(a) Translate FLAN into ASCII (4 bytes, big-endian order):
0x____________________
(b) Translate the key, STA1, into ASCII (same format as in part (a)):
0x____________________
(c) Show what happens when your answer to part (a) is XORed
with your answer to part (b). Give result here: 0x____________________
If you desire partial credit, please show your scratch work for the XOR
operations here:
(d) Now, prove that a hacker who did not know the original message (FLAN) could
recover it if he intercepted the encrypted message in part (c) and also knew
the key. Use at least one complete sentence. You must also show some work to
demonstrate that you know what you are talking about. However, you need not
show as much work as you did before.
15. (a) Write an unsimplified circuit diagram that takes 3 inputs (A, B, and
C) and produces a single output (W) that is given by the expression
(b) Prove that the expression in part (a) is equivalent to an IMP gate
involving inputs A and B only. A truth table proof with 8 rows is probably the easiest,
but there are other equally valid approaches that may save you some time. Use
your own judgment.
(c) Write a simplified circuit diagram for the expression in part (a), using
only one OR gate and an inverter someplace.