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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 463
432
INPUT/OUTPUT
CHAP. 5
29.
A disk manufacturer has two 5.25-inch disks that each have 10,000 cylinders. The
newer one has double the linear recording density of the older one.
Which disk proper-
ties are better on the newer drive and which are the same?
Are any worse on the newer
one?
30.
A computer manufacturer decides to redesign the partition table of a Pentium hard disk
to provide more than four partitions. What are some consequences of this change?
31.
Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in
that order.
A seek takes 6 msec per cylinder.
How much seek time is needed for
(a) First-come, first served.
(b) Closest cylinder next.
(c) Elevator algorithm (initially moving upward).
In all cases, the arm is initially at cylinder 20.
32.
A slight modification of the elevator algorithm for scheduling disk requests is to al-
ways scan in the same direction. In what respect is this modified algorithm better than
the elevator algorithm?
33.
A personal computer salesman visiting a university in South-West Amsterdam remark-
ed during his sales pitch that his company had devoted substantial effort to making
their version of UNIX very fast. As an example, he noted that their disk driver used
the elevator algorithm and also queued multiple requests within a cylinder in sector
order.
A student, Harry Hacker, was impressed and bought one.
He took it home and
wrote a program to randomly read 10,000 blocks spread across the disk.
To his amaze-
ment, the performance that he measured was identical to what would be expected from
first-come, first-served. Was the salesman lying?
34.
In the discussion of stable storage using nonvolatile RAM, the following point was
glossed over. What happens if the stable write completes but a crash occurs before the
operating system can write an invalid block number in the nonvolatile RAM?
Does
this race condition ruin the abstraction of stable storage?
Explain your answer.
35.
In the discussion on stable storage, it was shown that the disk can be recovered to a
consistent state (a write either completes or does not take place at all) if a CPU crash
occurs during a write. Does this property hold if the CPU crashes again during a recov-
ery procedure. Explain your answer.
36.
In the discussion on stable storage, a key assumption is that a CPU crash that corrupts
a sector leads to an incorrect ECC. What problems might arise in the five crash-recov-
ery scenarios shown in Figure 5-27 if this assumption does not hold?
37.
The clock interrupt handler on a certain computer requires 2 msec (including process
switching overhead) per clock tick. The clock runs at 60 Hz.
What fraction of the CPU
is devoted to the clock?
38.
A computer uses a programmable clock in square-wave mode. If a 500 MHz crystal is
used, what should be the value of the holding register to achieve a clock resolution of
(a) a millisecond (a clock tick once every millisecond)?
(b) 100 microseconds?
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