Structure and Function of the Processor (1.1.1)

Question 1

What is a computer processor?

Answer 1

A hardware device which runs the FDE cycle in order to execute instructions for programs to run.

Question 2

What is the function of the ALU?

Answer 2

The ALU carries out all arithmetical and logical operations.

Question 3

What is the control unit?

Answer 3

The control unit directs the operations of the CPU.

Question 4

What are the control unit’s jobs?

Answer 4

• Controlling and coordinating the activities of the CPU
• Managing the flow of data between the CPU and other devices
• Accepting the next instruction
• Decoding instructions
• Storing the resulting data back in memory

Question 5

What are registers?

Answer 5

Small, high speed memory cells that temporarily store data in the processor.

Question 6

What are the five main registers in the CPU?

Answer 6

• Program counter
• Accumulator
• Memory Address Register
• Memory Data Register
• Current Instruction Register

Question 7

What does the program counter do?

Answer 7

Holds the address of the next instruction to be executed.

Question 8

What does the accumulator do?

Answer 8

Stores the results of calculations made by the ALU.

Question 9

What does the memory address register do?

Answer 9

Stores the memory address of a location that will be read from or written to.

Question 10

What does the memory data register do?

Answer 10

Temporarily stores data that has been fetched from or will be written to the memory.

Question 11

What does the current instruction register do?

Answer 11

Holds the instruction currently being executed, divided into opcode and operand.

Question 12

What are buses?

Answer 12

A set of parallel wires which connect components within the CPU.

Question 13

Which three buses make the system bus?

Answer 13

• Data bus
• Control bus
• Address bus

Question 14

What is the width of the bus?

Answer 14

The number of parallel wires in the bus, it is directly proportional to the number of bits which can be transferred simultaneously.

Question 15

What is the data bus?

Answer 15

A bi-directional bus used for transporting data and instructions.

Question 16

What is the address bus used for?

Answer 16

Carries memory addresses which specify where data will be sent to or retrieved from. Width=number of addressable memory locations

Question 17

What is the control bus?

Answer 17

A bi-directional bus used to transmit control signals between internal and external components.

Question 18

What are some examples of control symbols?

Answer 18

• Bus request: shows a device wants to use the data bus
• Bus grant: shows a device has been allowed access to the data bus
• Memory write: data is written into the addressed location
• Memory read: data is read from a specific location and put on the data bus
• Interrupt request
• Clock: used for synchronisation

Question 19

What is assembly language?

Answer 19

A simplified way of expressing machine code using mnemonics- consisting of operand and opcode.

Question 20

What is the operand?

Answer 20

The data or address of data that will be manipulated

Question 21

What is the opcode?

Answer 21

The type of instruction to be executed.

Question 22

What is pipelining?

Answer 22

The process of completing the FDE cycles of three separate instructions simultaneously by having one instruction at each stage of the cycle at all times. It aims to reduce the amount of the CPU which is kept idle.

Question 23

What is the FDE cycle?

Answer 23

A sequence of operations that are completed to execute an instruction.

Question 24

What happens in the fetch phase?

Answer 24

• Address from PC is copied to MAR
• The address is sent to the memory along the address bus
• Instruction at address is copied to MDR along the data bus
• At the same time the PC increments by 1
• The value in the MDR is copied to the CIR

Question 25

What happens in the decode phase?

Answer 25

The contents of the CIR are split into operand and opcode

Question 26

What happens in the execute phase?

Answer 26

The decoded instruction is executed by the ALU and results are stored in the ACC->MDR->MEMORY

Question 27

What are the three factors that affect CPU performance?

Answer 27

• Clock speed
• Number of cores
• Amount and type of Cache memory

Question 28

What is clock speed?

Answer 28

The frequency at which the CPU executes instructions/ no. FDE cycles per second.

Question 29

What is the processor clock?

Answer 29

A timing device connected to the processor which synchronizes the FDE cycles.

Question 30

What is a core?

Answer 30

An independent processor in a CPU which can run its own FDE cycle.

Question 31

What are the benefits of having multiple cores?

Answer 31

Multiple FDE cycles can be completed at any time, however some programs are not designed to do this.

Question 32

What is cache memory?

Answer 32

The CPU’s on board memory which can be accessed much faster than main memory. The most frequently used instructions are stored here.

Question 33

What are the three main computer architectures?

Answer 33

• Von Neumann
• Harvard
• Contemporary

Question 34

What does the Von Neumann architecture consist of ?

Answer 34

• Single control unit
• ALU
• Registers
• Memory units
• Shared memory and data bus for both data and instructions.

Question 35

What is the stored program concept?

Answer 35

Used by the Von Neumann architecture, it states that machine code instructions are executed serially. They must be stored in the memory to be executed.

Question 36

What is the Harvard Architecture?

Answer 36

• There are separate memories and buses for instructions and data.
• Instructions and carried out serially
• Used by embedded processors and RISC processors

Question 37

Von Neumann ADVS

Answer 37

• Cheaper as control unit is easier to design

- Programs can be optimized in size

Question 38

Von Neumann DISADVS

Answer 38

-Having a shared bus for data and instructions can cause the “Von Neumann bottleneck”

Question 39

Harvard ADVS

Answer 39

• Quicker execution as data and instructions can be fetched in parallel.
• Memories can be different size allowing for efficient use of space

Question 40

What are contemporary processors?

Answer 40

A modified Harvard architecture whereby there is no strict separation of data and instructions but there are multiple memory buses.
Von Neumann architecture is used to communicate with main memory, Harvard is used with the cache.