COMPUTER BUSES AND PIPELINING TOPIC 7

Question 1

What is a Bus?

Answer 1

• Group of electrical conductors that carry computer/electrical signals from one location to another

Question 2

What is the function of a bus?

Answer 2

• Computer transfers data between components

Question 3

What does a bus physically consist of?

Answer 3

• WIRES
• CONDUCTORS on a printed circuit
• LINE

Question 4

What is the purpose of a bus hierarchy?

Answer 4

An interconnection system used when a single system bus cannot provide the degree of connectivity required

Question 5

4 Main categories of Bus Lines

Answer 5

1. Data lines
   - Carry data
2. Address lines
   - Specify the recipient of data
3. Control lines
   - Provide control for the synchronisation of the bus
4. Power lines
   - Provide power to various components

Question 6

Data Bus

Answer 6

• Carries data between the CPU and memory
  Bi-directional
• Typical sizes 64 bit

Question 7

Address bus

Answer 7

• Carries an address from the CPU to memory
• Unidirectional
• Typical sizes 16,20,24 lines

Question 8

Control bus

Answer 8

• Collection of signals for coordinating CPU activities
• Typical sized 10-20 lines
• Bidirectional

Question 9

CALCULATIONS

Answer 9

Size of MAR = size of address bus = 18
No of memory locations = 2^18 = = 262,144 bites memory locations
Size of MDR = size each memory location = 16 = 2 Bytes
Size of addressable memory = = 262144 x 2 bytes = 524,288 Bytes = 512 KB
= 4,194,304 Bits

Question 10

Bus topologies

Answer 10

1. Point-To-Point bus
2. Multipoint/ Multidrop bus

Question 11

What is a pipeline?

Answer 11

• A technique of improving the performance of a machine by overlapping to reduce the overall execution time

Question 12

Pipeline Problems

Answer 12

1. Data dependency
   - A problem arises when two adjacent instructions accessing the same data within the same memory location
2. Branching of Instructions
   - When the other pre-fetched instructions in the pipeline have to be discarded

Question 13

Solution for problems:

Answer 13

• Hardware and software based approach for data dependency
• Instruction reordering for branch problem

Question 14

Hardware implementation

Answer 14

Hardware – operations are implemented directly by logic gates (hardwired)
Advantages:
- Speed
- RISC designs are simple and typically implemented in hardware

Question 15

Microprogrammed implementation

Answer 15

Microcodes are tiny programs stored in ROM that replaces CPU instructions.
Advantages:
More flexible
- Easier to implement complex instructions
- Can emulate other CPUs
Disadvantage:
- Requires more clock cycles