Input/Output

Question 1

What is considered I/O?

Answer 1

Any transfer of data to or from the CPU / memory

Question 2

What are point - to - point connections?

Answer 2

pairwise connections between nodes. No addresses needed, lots of wires for lots of connections.

Question 3

What is a mesh network?

Answer 3

Pairwise connections between nodes, nodes route messages between addresses. Can get messy and slow

Question 4

What is bus architecture?

Answer 4

Every node has equal access to a shared network called the bus.

Question 5

How does a node send a message to another node in bus architecture?

Answer 5

• Announce who the message is for. (Address)
• Announce what type of message it is
• Announce the data
• Ensure the above signals don’t collide.

Question 6

Advantages of a bus architecture ?

Answer 6

Easy to add new devices, low cost as not many connections are needed.

Question 7

Disadvantages of a bus architecture ?

Answer 7

The bus can bottleneck the whole network, and the performance can be limited by other physical factors (bus length, number of connections)

Question 8

What is the address line ?

Answer 8

It designates the source and destination of data on the bus.

Question 9

What detirmines the bus capacity ?

Answer 9

The width of the bus.

Question 10

What are data and control lines ?

Answer 10

Data lines transport data, control lines transport data and address lines. Provides command and timing info for the nodes.

Question 11

How do you calculate bandwidth ?

Answer 11

bandwidth = lane speed * number of lanes

Question 12

What registers in the CPU control I/O ?

Answer 12

MAR (Memory Address Register) holds addresses of read / write to go on address lines. MBR (Memory Buffer Register) holds data to go on the data line.

Question 13

What is an I/O module ?

Answer 13

I/O modules act as RAM within memory addresses. Can send commands and data to the I/O module, we can also read / write from the module.

Question 14

How does the I/O module handle work ?

Answer 14

Not as fast as the CPU but can manage instructions independent of the CPU (Parallelisation)

Question 15

How does the I/O module send data to peripherals ?

Answer 15

The CPU rate is high ,therefore, the data is buffered in the I/O module and sent to the peripheral at its own rate. The I/O module also manages errors from the peripherals

Question 16

What is the difference between I/O module and device drivers ?

Answer 16

I/O module is hardware on the bus connected to the CPU. Device drivers are responsible for the communication between the perihperal and I/O module.

Question 17

What is polling I/O ?

Answer 17

The CPU periodically checks the status of the I/O module until the operation is complete. Simple to implement but inefficient.

Question 18

What is interrupt driven I/O ?

Answer 18

When the I/O operation is done it sends an interrupt request ot the CPU.

Question 19

What is Direct Memory Access I/O ?

Answer 19

Takes I/O communcation from the CPU, sends interrupt request when done. Used in large data movment. Frees the CPU but can clog the bus.

Question 20

What can be used rather than a I/O module ?

Answer 20

Memory Mapped I/O:
Assign dedicated RAM to represent devices. Devices read from the memory itself. Used as VRAM.
CPU I/O Pins:
Dedicated pins on the CPU for I/O. Frees up bus and address space. Used in embedded systems.

Question 21

What is the bus hierachy ?

Answer 21

• Northbridge (Connects to the CPU, RAM, PCIe, GPU)
• Southbridge (I/O modules, migrated onto a single chip)

Question 22

What is PCIe ?

Answer 22

General purpose data transfer for internal peripherals. Not really a bus more of a mesh.

Question 23

What is USB ?

Answer 23

Standardised for connecting to peripheral devices. Not really a bus, point-to-point connection. manager / worker protocol.