Input/Output - Week 8

Question 1

What is Input/Output (I/O)?

Answer 1

Any transfer of information between the computer and the external world.

Question 2

What are the basic ways to transfer information between the computer and external devices

Answer 2

Programmed I/O
Interrupts
Direct memory access

Question 3

How are I/O devices controlled

Answer 3

Busy waiting
Polling
Interrupts

Question 4

How is data transfer managed

Answer 4

Memory mapping
Cycle stealing
Buffering

Question 5

In the von Neumann model, what counts as I/O?

Answer 5

Any transfer beyond CPU and main memory.

Question 6

Why is I/O challenging?

Answer 6

Devices vary in speed, format, and data volume, and are slower than CPU/RAM.

Question 7

What are the five functions of an I/O module?

Answer 7

Control & timing
Processor communication
Device communication
Data buffering
Error detection.

Question 8

What is the purpose of data buffering?

Answer 8

To balance speed differences between CPU/memory and devices.

Question 9

What are the 3 techniques for I/O operations

Answer 9

Programmed I/O
Interrupt-driven I/O
Direct memory access

Question 10

What is programmed I/O?

Answer 10

CPU waits for device to finish I/O before continuing.

Question 11

Main disadvantage of programmed I/O?

Answer 11

If the processor is faster than the I/O module this is wasteful of processor time

Question 12

What is interrupt‑driven I/O?

Answer 12

Processor sends an I/O request, then continues doing other work.

When the device finishes, it sends an interrupt to tell the CPU, which pauses, handles it, then carries on.

The parent tells the kid to do a chore, then carries on with their own work. When the kid finishes, they come back and interrupt the parent, who pauses, deals with them, then continues working.

Question 13

What is DMA?

Answer 13

The I/O module and main memory exchange data directly without processor involvement

Question 14

Which I/O technique has no interrupts and has I/O to memory transfer through processor

Answer 14

Programmed I/O

Question 15

Which I/O technique uses interrupts and has I/O to memory transfer through processor

Answer 15

Interrupt driven I/O

Question 16

Which I/O technique uses interrupts and has direct I/O to memory transfer

Answer 16

Direct memory access

Question 17

What is the first step in controlling I/O devices

Answer 17

A stored instruction is fetched to the IR in the CPU and turns out, upon decoding, to be an I/O operation.

Question 18

What happens after an I/O instruction is decoded?

Answer 18

An instruction from the control unit to the I/O control unit causes the I/O control unit to send signals to the device to set it into action.

Question 19

What must happen after the device is set into action?

Answer 19

Data will need to be transferred to the device (a write) or from the device (a read).

Question 20

Where is the data placed during I/O transfers?

Answer 20

A data register.

Question 21

What must the I/O instructions be structured and coded into a bit pattern with 3 parts describe

Answer 21

An I/O operation code
The direction of transfer
The address of the device

Question 22

Where is I/O data placed in multiple device control?

Answer 22

I/O data is placed on a common I/O data bus.

Question 23

Where is address information placed in multiple device control?

Answer 23

can also be placed on a common I/O address bus.

Question 24

Whats the main advantages of having a shared I/O bus

Answer 24

Simplicity and flexibility - a single I/O control system with a single connection to the CPU.

Question 25

What are the disadvantages of having a shared I/O bus

Answer 25

Cost of building a shared bus Possibility of contention for the shared resources of the bus

Question 26

What is memory‑mapped I/O?

Answer 26

Memory-mapped I/O is when I/O devices are assigned addresses in memory, allowing the processor to interact with them using standard memory instructions (load and store).

Question 27

Advantages of memory mapping

Answer 27

Simplifies I/O control, freeing CPU space for other uses

Question 28

Disadvantages of memory mapped I/O

Answer 28

Uses address space, which then cant be used for storage I/O devices are in contention with the store for the same bus Programs may be harder to understand, as I/O and storage can be confused

Question 29

What is the major problam with I/O programming

Answer 29

I/O device operation often involves some sort of electro-mechanical process This is much slower than electronic transfer of data within a CPU ** SLOW

Question 30

Describe the busy wait strategy

Answer 30

Load next data to send to I/O device x Initiate I/O device x Test I/O device x's status flag If flag not set, repeat last instruction wait write data to device

Question 31

Describe polling strategy

Answer 31

load next data to send to I/O device x; initiate I/O device x; test I/O device x’s status flag; if flag not set, do something else for a while, and go to previous step (test) write data to device

Question 32

Advantage of polling

Answer 32

Allows us to get on with background computation

Question 33

Disadvantages of polling

Answer 33

Unresponsiveness Multiple devices Complexity

Question 34

What are the protocols for programmed I/O transfer using device flags

Answer 34

Busy waiting Polling