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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
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Page 461
controller, how long will it take to transfer 1000 words from the disk controller to main
memory, if (a) word-at-a-time mode is used, (b) burst mode is used? Assume that com-
manding the disk controller requires acquiring the bus to send one word and acknowl-
edging a transfer also requires acquiring the bus to send one word.
One mode that some DMA controllers use is to have the device controller send the
word to the DMA controller, which then issues a second bus request to write to mem-
How can this mode be used to perform memory to memory copy? Discuss any
advantage or disadvantage of using this method instead of using the CPU to perform
memory to memory copy.
Suppose that a computer can read or write a memory word in 5 nsec. Also suppose that
when an interrupt occurs, all 32 CPU registers, plus the program counter and PSW are
pushed onto the stack. What is the maximum number of interrupts per second this ma-
chine can process?
CPU architects know that operating system writers hate imprecise interrupts.
One way
to please the OS folks is for the CPU to stop issuing new instructions when an interrupt
is signaled, but allow all the instructions currently being executed to finish, then force
the interrupt.
Does this approach have any disadvantages? Explain your answer.
In Fig. 5-9(b), the interrupt is not acknowledged until after the next character has been
output to the printer. Could it have equally well been acknowledged right at the start of
the interrupt service procedure?
If so, give one reason for doing it at the end, as in the
text. If not, why not?
A computer has a three-stage pipeline as shown in Fig. 1-7(a). On each clock cycle,
one new instruction is fetched from memory at the address pointed to by the PC and
put into the pipeline and the PC advanced. Each instruction occupies exactly one mem-
ory word. The instructions already in the pipeline are each advanced one stage. When
an interrupt occurs, the current PC is pushed onto the stack, and the PC is set to the ad-
dress of the interrupt handler. Then the pipeline is shifted right one stage and the first
instruction of the interrupt handler is fetched into the pipeline. Does this machine have
precise interrupts?
Defend your answer.
A typical printed page of text contains 50 lines of 80 characters each. Imagine that a
certain printer can print 6 pages per minute and that the time to write a character to the
printer’s output register is so short it can be ignored. Does it make sense to run this
printer using interrupt-driven I/O if each character printed requires an interrupt that
takes 50
sec all-in to service?
Explain how an OS can facilitate installation of a new device without any need for
recompiling the OS.
In which of the four I/O software layers is each of the following done.
(a) Computing the track, sector, and head for a disk read.
(b) Writing commands to the device registers.
(c) Checking to see if the user is permitted to use the device.
(d) Converting binary integers to ASCII for printing.
A local area network is used as follows. The user issues a system call to write data
packets to the network. The operating system then copies the data to a kernel buffer.

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