Deck 12: Io Systems

Question 1

Which of the following principles is used to improve the efficiency of I/O?

A) Reduce the number of times that data must be copied in memory while passing between device and application.
B) Move processing primitives into hardware, to allow their operation in device controllers to be concurrent with CPU and bus operation.
C) Increase concurrency by using DMA-knowledgeable controllers or channels to offload simple data copying from the CPU. 

D) All of the above.

Answer 1

D

Question 2

Component that measures elapsed time and to trigger operations is called a

A) programmable interval timer.
B) high performance event timer.
C) network time protocol.
D) socket.

Answer 2

A

Question 3

Which of the following is FALSE about streams?

A) A stream is a full-duplex connection between a device driver and a user-level process.
B) Each stream module contains a pair of queues.
C) The number of modules in a stream is fixed by the operating system.
D) Messages may be dropped in a stream even if flow control is implemented.

Answer 3

C

Question 4

Explain the concept of a bus and daisy chain. Indicate how they are related.

Question 5

Technique used to improve I/O efficiency by temporarily storing copies of data is called

A) spooling.
B) buffering.
C) caching.
D) memory mapping.

Question 6

In memory-mapped I/O

A) main memory of the computing device is used for communicating with the I/O devices using the standard I/O instructions.
B) main memory of the computing device is used for communicating with the I/O devices using the special I/O instructions.
C) address space of the computing device is used for communicating with the I/O devices using the standard I/O instructions.
D) address space of the computing device is used for communicating with the I/O devices using the special I/O instructions.

Question 7

In polling I/O, the main inefficiency comes from

A) the hardware controller when it notifies the CPU that the device is ready for service.
B) the basic polling operation that may be comprised of several CPU instructions.
C) polling when it is attempted repeatedly yet rarely finds a device ready for service.
D) the slow data transfer rate between a device and the host.

Question 8

What is interrupt chaining?

Question 9

Interrupt chaining

A) allows CPU to defer processing of low-priority interrupts without masking all interrupts.
B) splits interrupt management between first level and second level interrupt handlers.
C) is used to handle interrupts but not exceptions.
D) is a compromise between the overhead of a huge interrupt table and the inefficiency of dispatching to a single interrupt handler.

Question 10

A current trend in I/O device technology and I/O subsystem is

A) there is an increasingly broad variety of I/O devices.
B) new devices are similar to the previous I/O devices that makes it easier to incorporate them in operating systems.
C) to encapsulate the oddities of different I/O devices, the device drivers present device-specific interface for each device to the I/O subsystem.
D) All of the above.

Question 11

In a blocking system call, the execution of a process is suspended

A) until the process is woken up by some other process.
B) until a fixed amount of time has elapsed.
C) the kernel raises the priority of that process.
D) the I/O has completed.

Question 12

Which of the following is TRUE about a serial port controller and a fibre channel (FC) bus controller?

A) Both FC bus controller and serial port controller are often implemented as separate circuit boards.
B) A serial-port controller is a simple device controller, while an FC bus controller is complex.
C) Both FC bus controller and serial port controller are used in PCs.
D) All of the above.

Question 13

Which of the following is NOT a technique used for managing power consumption in mobile devices?

A) Power collapse.
B) chilling with natural sources such as lake water, and solar panels.
C) Component level power management.
D) Wakelocks.

Question 14

A control register in an I/O device control

A) is written by the host to send output.
B) is written by the host to choose half-duplex communication.
C) is read by the host to get input.
D) contains status bits that can be read by the host.

Question 15

Explain the concept of polling between a host and a controller.

Question 16

Escape (or back door) in application I/O interface

A) allows a user to interrupt a device at any time.
B) allows access to a few additional devices, such as a time-of-day clock and a timer.
C) transparently passes arbitrary commands from an application to a device driver.
D) enables managing of devices with widely varying speeds ranging from a few bytes per second to gigabytes per second.

Question 17

Explain the difference between a serial-port controller and a SCSI bus controller.

Question 18

Why is DMA used for devices that execute large transfers?

Question 19

Buffering in I/O is used to

A) cope with a speed mismatch between the producer and consumer of a data stream.
B) provide adaptations for devices that have different data-transfer sizes.
C) support copy semantics for application I/O.
D) All of the above.

Question 20

In DMA-based I/O,

A) CPU is relieved from data transfer and is interrupted after every word has been transferred to initiate the next word transfer.
B) cycle stealing can slow down the CPU computation, but off-loading the data-transfer work to a DMA controller generally improves the total system performance.
C) interrupt mechanism is not used.
D) data is transferred to/from a single block of memory, but not to/from multiple blocks.

Question 21

In UNIX, part of a path name includes a device name.

Question 22

What is the purpose of a UNIX mount table?

Question 23

A maskable interrupt can never be disabled.

Question 24

What is the purpose of a programmable interval timer?

Question 25

Give an example of when an application may need a nonblocking I/O system call.

Question 26

Vectored IO allows one system call to perform multiple IO operations involving a single location.

Question 27

An expansion bus is used to connect relatively high speed devices to the main bus.

Question 28

What are the three reasons that buffering is performed?

Question 29

An I/O system call returns a one-bit information about the status of the call.

Question 30

A dedicated device cannot be used concurrently by several processes or threads.