Bus Architectures (PPT 13)

Question 1

What is a Bus?

Answer 1

It is a pathway that inter connects two or more components in a computer

Question 2

What is a bus made up of?

Answer 2

A bus is made up of a number of lines which collectively carry a signal. Any signal put onto a bus can be received by all other components connected to the bus

Question 3

What is a bus hierarchy?

Answer 3

This is a collection of interconnected buses. This allows the CPU to talk to memory and I/O devices

Question 4

What are the two defining factors of PC architecture over the years?

Answer 4

• CPU architecture

- Bus architecture

Question 5

What has been the trend for I/O demand over the years?

Answer 5

Initially there was little I/O demand so generic devices were used to handle it. Now, there is more I/O so we use more specialised devices to deal with each I/O device

Question 6

What is the effect of more specialised I/O devices?

Answer 6

The computer is faster but it is more complex

Question 7

What are the two main areas we wish to improve when revising bus architecture?

Answer 7

-Data Transfer Rate:
Want to support high transfer rate to service high demand

Want high demand devices to be closely integrated with CPU

Want CPU-memory communication to be separate from other communication

-Compatibility
Want I/0 chips to be independent of the CPU

Want backwards compatibility with existing chips

Question 8

What are the four typical types of buses which a PC has?

Answer 8

• Local bus
• System bus
• High Speed bus
• Expansion bus

Question 9

What is the Local Bus?

Answer 9

It connects the CPU to cache memory and the bridge chip. It is very fast, about 500 MHz

Question 10

What is the System Bus?

Answer 10

Connects CPU to main memory. Fairly fast, about 100 MHz

Question 11

What is the High Speed Bus?

Answer 11

Supports high speed peripherals, about 33 MHz

Question 12

What is the Expansion Bus?

Answer 12

Supports medium/low speed peripherals. Provides backwards compatibility with existing I/O chips. About 8 MHz

Question 13

Give an example of a expansion bus

Answer 13

Industry Standard Architecture (ISA) bus

Question 14

Give an example of a high speed bus

Answer 14

Peripheral Component Interconnect (PCI) bus

Question 15

What is time-multiplexing?

Answer 15

This is when certain lines are used alternatively to transfer address and data

Question 16

What is block mode on a PCI?

Answer 16

Allows faster block transfer as only the first address and size of the block is needed for transfer

Question 17

What is arbitration, in relation to the DMA?

Answer 17

Arbitration is a scheme used to resolve requests from different bus masters, e.g. CPU and DMA. Could be 1st come 1st serve or round robin, for example

Question 18

What was the problem with parallel buses and how did using serial solve this?

Answer 18

While parallel buses are fast at carrying multiple signals, the sheer amount of devices was clogging them up. This was solved by connecting devices point to point using high speed serial links. The new serial standards are similar to network standards

Question 19

What is USB?

Answer 19

Universal Serial Bus

Was designed as the replacement for all serial and parallel peripherals

Question 20

What are the benefits of USB?

Answer 20

-Fast, robust and simple so therefore cheap
-Hot swappable, meaning you don’t need to turn off the power to remove it
-3 speeds (low, full, hi)
It was widely adopted because of these features

Question 21

What is PCIe?

Answer 21

PCI Express was designed to replace PCI. It is a scalable, serial point to point bus based on lanes. Lanes can carry 256 MBps in each direction with faster transfers being allowed to use more than one lane

Question 22

What is SATA?

Answer 22

Serial Advanced Technology Attachment

Similar to other buses, it is serial, point to point and hot-swappable

Question 23

What does each bus contain?

Answer 23

Each bus has a:

• address bus
• data bus
• control bus

Question 24

What does a typical PC system unit contain?

Answer 24

• Motherboard (with CPU, Memory, etc)
• adapter boards (in motherboards expansion slots)
• Power supply
• Drive expansion bays for hard drives or cd/dvds

Question 25

What are the typical parts of a motherboard?

Answer 25

• CPU
• Cache/RAM + controller chip
• Bridge Chips
• Integrated adapters and expansion ports
• ROM BIOS
• Real time clock/calender

Question 26

What is ROM BIOS?

Answer 26

This loads the basic operation system software from the start up device. It also performs the on power tests. It is usually 64-128kb and is stored on DRAM for faster execution. It also allows for system configuration