Hardware Reference
In-Depth Information
is the total information capacity (in bits) of the human genome? What is the maximum
information capacity (in bits) of the average gene?
11.
A certain computer can be equipped with 1,073,741,824 bytes of memory. Why would
a manufacturer choose such a peculiar number, instead of an easy-to-remember num-
ber like 1,000,000,000?
12.
Devise a 7-bit even-parity Hamming code for the digits 0 to 9.
13.
Devise a code for the digits 0 to 9 whose Hamming distance is 2.
14.
In a Hamming code, some bits are ''wasted'' in the sense that they are used for check-
ing and not information. What is the percentage of wasted bits for messages whose
total length (data + check bits) is 2
n
−
1? Evaluate this expression numerically for val-
ues of
n
from 3 to 10.
15.
An extended ASCII character is represented by an 8-bit quantity. The associated Ham-
ming encoding of each character can then be represented by a string of three hex digits.
Encode the following extended five-character ASCII text using an even-parity Ham-
ming code: Earth. Show your answer as a string of hex digits.
16.
The following string of hex digits encodes extended ASCII characters in an even-parity
Hamming code: 0D3 DD3 0F2 5C1 1C5 CE3. Decode this string and write down the
characters that are encoded.
17.
The disk illustrated in Fig. 2-19 has 1024 sectors/track and a rotation rate of 7200
RPM. What is the sustained transfer rate of the disk over one track?
18.
A computer has a bus with a 5-nsec cycle time, during which it can read or write a
32-bit word from memory. The computer has an Ultra4-SCSI disk that uses the bus
and runs at 160 Mbytes/sec. The CPU normally fetches and executes one 32-bit in-
struction every 1 nsec. How much does the disk slow down the CPU?
19.
Imagine you are writing the disk-management part of an operating system. Logically,
you represent the disk as a sequence of blocks, from 0 on the inside to some maximum
on the outside. As files are created, you have to allocate free sectors. You could do it
from the outside in or the inside out. Does it matter which strategy you choose on a
modern disk? Explain your answer.
20.
How long does it take to read a disk with 10,000 cylinders, each containing four tracks
of 2048 sectors? First, all the sectors of track 0 are to be read starting at sector 0, then
all the sectors of track 1 starting at sector 0, and so on. The rotation time is 10 msec,
and a seek takes 1 msec between adjacent cylinders and 20 msec for the worst case.
Switching between tracks of a cylinder can be done instantaneously.
21.
RAID level 3 is able to correct single-bit errors using only one parity drive. What is
the point of RAID level 2? After all, it also can correct only one error and takes more
drives to do so.
22.
What is the exact data capacity (in bytes) of a mode-2 CD-ROM containing the
now-standard 80-min media? What is the capacity for user data in mode 1?
23.
To burn a CD-R, the laser must pulse on and off at a high speed. When running at 10x
speed in mode 1, what is the pulse length, in nanoseconds?
