Computer Architectures

Question 1

What are the features of Von Neumann architecture?

Answer 1

• Fetch.Decode.Execute cycle
• One instruction processed at a time.
• Single control unit (manages program control)
• Programs are stored with data in the same format

Question 2

Name the registers used by the processor.

Answer 2

• memory address register
• memory data register
• current instruction register
• accumulator
• interrupt register
• index register

Question 3

Describe the fetch-execute cycle.

Answer 3

• PC holds address of next instruction
• copy contents of PC to MAR
• increment PC
• load instruction pointed to by the MAR to MDR
• copy instruction from MDR to CIR
• decode instruction in CIR

Question 4

Describe how a jump instruction is executed.

Answer 4

copying address part of the instruction in CIR to the PC

Question 5

Name six architecture types.

Answer 5

• Von Neumann
• Co-Processor
• Parallel Processor
• Array Processor
• RISC
• CISC

Question 6

Describe a parallel processor system.

Answer 6

• More than one processor.
• Processors work together to perform a single job.
• Jobs are split into tasks.
• Each task can be processes by any processor/
• Processors are controlled by a complex operating system.

Question 7

Describe an array processor.

Answer 7

• A processor that allows the same instruction to operate simultaneously on multiple data locations.
• It uses multiple ALUs.
• Single Instruction Multiple Data
• The same calculation on multiple data is very fast.

Question 8

What does RISC stand for?

Answer 8

Reduced Instruction Set Computer

Question 9

What does CISC stand for?

Answer 9

Complex Instruction Set Computer

Question 10

State features of RISC?

Answer 10

• limited number of instructions available
• an instruction performs a simple task
• complex tasks can only be performed by combining a number of instructions
• complex tasks can take more than one machine cycle

Question 11

Describe the use of the MDR.

Answer 11

• Instruction/data from address in MAR is copied to MDR
• instruction in MDR is copied to CIR
• MDR acts as a buffer/temporary store
• MDR contains data/instructions…
• …when being transferred between memory & processor

Question 12

Explain the use of the accumulator in the processor.

Answer 12

• holds data being processed
• temporary storage of intermediate results (in the
  ALU)
• is where calculations are performed
• input & output data passes through

Question 13

Explain the term register.

Answer 13

• a location in the processor
• used for a particular purpose
• (temporarily) stores data/or control information
• explained example of contents held by named register

Question 14

Give the advantages of using parallel processor systems.

Answer 14

• allows faster processing
• more than one instruction (of a program) is processed at the same time
• different processors can handle different tasks/parts of same job

Question 15

Give the disadvantages of using parallel processor systems.

Answer 15

• operating system is more complex…
• …to ensure synchronisation
• program has to be written in a suitable format
• Program is more difficult to test/write/debug

Question 16

State features of Complex Instruction Set Computer.

Answer 16

- uses (complex) instructions each of which may take
multiple cycles
- single register set
- instructions have variable format
- many instructions are available
- many addressing modes are available

Question 17

What is the disadvantage of using CISC over RISC?

Answer 17

• programs run more slowly…

- …due to the more complicated instructions/circuit

Question 18

How does the contents of MAR change during the fetch-execute cycle?

Answer 18

• Receives address of instruction/data (from PC)
• Holds address of data/instruction to be used
• Receives operand part of instruction from CIR.

Question 19

How does the contents of MDR change during the fetch-execute cycle?

Answer 19

• Receives an instruction/data
• …from memory location in MAR
• Receives data/instruction from…
• …memory location in address part of instruction/accumulator.