Input/Output Management

Question 1

What is the purpose of I/O devices?

Answer 1

I/O devices enable computers to receive or output information to humans or devices.

Question 2

Give three examples of I/O devices.

Answer 2

• Human interface devices (e.g., monitors)
• Storage devices (e.g., disks)
• Transmission devices (e.g., network cards)

Question 3

How are I/O devices operated?

Answer 3

I/O devices are operated using controllers (embedded processors).

Question 4

What is the role of controller registers?

Answer 4

The CPU communicates with the controller by reading and writing to the controller’s registers.

Question 5

What are the two types of I/O access methods?

Answer 5

• Port-based I/O
• Memory-mapped I/O

Question 6

Which I/O access method is more common today?

Answer 6

Memory-mapped I/O is today much more common than port-based I/O.

Question 7

What are the two approaches to control in I/O management?

Answer 7

• Polling
• Interrupts

Question 8

Describe polling in I/O management.

Answer 8

The CPU repeatedly checks the controller’s status register to see whether the controller is busy. When the controller is ready and the CPU wants to give new instructions, the CPU writes to the data-out register and signals that is has done so through the control register.

Question 9

What happens when the CPU receives an interrupt signal?

Answer 9

The CPU stops the current process and initiates a response.

Question 10

Compare polling and interrupts.

Answer 10

With interrupts, the CPU can monitor several devices at the same time; with polling, the CPU checks each device individually in a round robin fashion.

Question 11

When might polling be more efficient?

Answer 11

• The controller and the device are fast
• The I/O rate is high
• Some I/O data can be ignored
• The CPU has nothing better to do

Question 12

What is Direct Memory Access (DMA)?

Answer 12

DMA allows a CPU to offload large data transfers to a DMA controller, which can perform multiple transfers via a single command.

Question 13

What is a system call?

Answer 13

A system call is a request of a kernel service.

Question 14

What are the types of system calls for I/O devices?

Answer 14

• Character I/O
• Block I/O
• Network I/O

Question 15

What are examples of character I/O devices?

Answer 15

• Keyboards
• Computer mice
• Microphones
• Speakers

Question 16

What is the primary characteristic of block I/O devices?

Answer 16

Block devices are used to transfer blocks of data and are typically non-volatile mass storage devices. They are high volume devices and include read and write operations

Question 17

What is a memory-mapped interface in block I/O?

Answer 17

It provides access to disk storage via a location in main memory, mapping a file on the device into memory.

Question 18

What operations are included in network I/O?

Answer 18

• Creating and connecting sockets
• Sending and receiving packets
• Checking transfer success

Question 19

True or False: Network I/O devices are less prone to issues than other I/O devices.

Answer 19

False.
The main difference between network I/O devices and other I/O devices is that with network I/O devices things routinely go wrong (missing packets, etc.).

Question 20

What is the difference between port-based and memory mapped I/O

Answer 20

port-based separates memory and I/O operations and address space while memory mapped does not.

Question 21

Where does the CPU get an interrupt signal from

Answer 21

an interrupt request line

Question 22

How does the DMA let the CPU know when the transfer is complete

Answer 22

the CPU receives an interrupt from the DMA controller

Question 23

What is user mode used for

Answer 23

application programs; plain instructions

Question 24

What is kernel mode used for

Answer 24

system functions; privileged instructions

Question 25

How are characters I/O processed

Answer 25

in the order that they arrive in the stream

Question 26

What are character devices

Answer 26

they are low volume devices

Question 27

Explain memory mapped I/O

Answer 27

In this case, the device-control registers are mapped into the address space of the processor. The CPU executes I/O requests using the standard data-transfer instructions to read and write the device-control registers at their mapped locations in physical memory.

Question 28

Explain special I/O instructions

Answer 28

specify the transfer of a byte or a word to an I/O port address. The I/O instruction triggers bus lines to select the proper device and to move bits into or out of a device register.

Question 29

What does a DMA command block contain that has been written into memory

Answer 29

This block contains a pointer to the source of a transfer, a pointer to the destination of the transfer, and a count of the number of bytes to be transferred.

Question 30

What does memory mapped files do

Answer 30

reduce the number of mode switches

Question 31

What is the benefit of memory mapped I/o instruction wise

Answer 31

The more instructions the complex the intructions are, the more bits you need. Therefore memeory mapped i/o there are less instructions which is better

Question 32

What is the bus analog for interrupts vs polling

Answer 32

Polling: at every stop the bus driver(cpu) has to ask every passenger if we need to stop Interrupts: stops only when it is singaled to rather than cehcking every passenger every time. Therefore quicker With interrupts the driver can manager all pasengers at the same time. Ther driver can focus more on driving the bus - therefore freed up to focus on other tasks.

Question 33

Why is interrupts more efficient

Answer 33

monitor the status of several devices at the same time, and serve them based on priority.