I/O Management

Question 1

How is communicating with I/O devices handled?

Answer 1

Communication takes place over a cable known as a Bus, and is operated by Controllers.

Question 2

What are the 4 types of registers used in I/O communication?

Answer 2

Data-In register, Data-out register, Status Register, Control Register

Question 3

what is stored in the Control Register?

Answer 3

Commands to the device such as save, write, transfer, and read commands.

Question 4

How does Port based I/O work?

Answer 4

Special Instructions are used to transfer a small number of bytes to an I/O bus address

Question 5

How does Memory-Mapped I/O work?

Answer 5

Standard Memory Instruction used by treating the device as memory and writing/reading from the location.

Question 6

What is Polling?

Answer 6

CPU checks controller status, when status is ready CPU writes to Data Out register then Controller. CPU is much faster than I/O so most Poll’s are unsuccessful.

Question 7

What are I/O Interrupts?

Answer 7

When the I/O device wants to give an input its send san interrupt to the CPU in order to initiate the appropriate process.

Question 7

What are I/O Interrupts?

Answer 7

When the I/O device wants to give an input its send san interrupt to the CPU in order to initiate the appropriate process.

Question 8

In which circumstances is polling appropriate?

Answer 8

If the controller and device are fast in relation to the CPU, if the I/O rate is high, if some I/O data can be ignored, if the CPU is not engaged in other processes.

Question 9

How are large data transfers handled?

Answer 9

These are inefficient if done byte by byte, this work is offloaded to a special purpose processor (Direct Memory Access Controller) so that the CPU can handle other processes.

Question 10

How does the Direct Memory Access Controller work?

Answer 10

CPU writes a command block to memory specifying source and destination of transfer. DMA controllers can handle multiple transfers at the same time.

Question 11

How do Device Drivers Function?

Answer 11

Device Drivers hide the differences between various device controllers by defining an interface between the OS and I/O devices. Device Drivers are loaded as modules into the kernel.

Question 12

Which devices are Character I/O devices?

Answer 12

Keyboard, mouse, microphones, and speakers

Question 13

How is data sent to Character I/O’s?

Answer 13

Data is sent in a stream of bytes. Characters must be processed in the order they arrive in the stream.

Question 14

Which interfaces are used by Character I/O’s

Answer 14

Get operation, Put operation, Libraries for line-by-line access.

Question 15

Which devices are Block I/O?

Answer 15

Non-Volatile Storage devices

Question 16

How is data sent for Block I/O’s?

Answer 16

Data is transferred in Blocks, the order of the data doesn’t matter as long as everything is correct and uncorrupted. DMAC is used for transfer.

Question 17

How are memory mapped files handled?

Answer 17

Address range from disk is taken and mapped to memory, data is written to the memory and the CPU can synch the disk with memory at any time.

Question 18

Which interface instructions do Network I/O devices have?

Answer 18

Create and connect sockets, send and receive packets, select function, for determining status of sockets. System functions also included for checking if transfer is successful, and recovering form unsuccessful transfer.