1.1.1 Structure/Function of Processor (old)

Question 1

What does the ALU do?

Answer 1

It completes all of the arithmetical and logical operations.

Question 2

What do arithmetical and logical operations include?

Answer 2

Arithmetical operators include all mathematical operations such as addition and subtraction on fixed or floating point numbers.

Logical operations include Boolean logical operators such as AND, OR, NOT and XOR.

Question 3

What is the control unit?

Answer 3

The component of the processor which directs the operations of the CPU.

Question 4

What are the jobs of the Control Unit?

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 memory cells that operate at a very high speed.

Question 6

What are registers used for?

Answer 6

They are used to temporarily store data and all arithmetic, logical and shift operations occur in these registers.

Question 7

What does the Program Counter (PC) do?

Answer 7

Holds the address of the next instruction to

be executed.

Question 8

What does the Accumulator (ACC) do?

Answer 8

Stores the results from calculations

Question 9

What does the Memory Address Register (MAR) do?

Answer 9

Holds the address of a location that is to be

read from or written to.

Question 10

What does the Memory Data Register (MDR) do?

Answer 10

Temporarily stores data that has been read or data that needs to be written.

Question 11

What does the Current Instruction Register (CIR) do?

Answer 11

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

Question 12

What is a bus?

Answer 12

A physical set of parallel wires connecting and carrying groups of bits between several components of a computer.

Question 13

What are the three buses in the CPU?

What are they collectively called?

Answer 13

The data bus, the control bus, the address bus.

They are collectively called the system bus.

Question 14

What is the width of the bus?

Answer 14

The number of parallel wires the bus has.

Question 15

What is the width of the bus directly proportional to?

Answer 15

The width of the bus is directly proportional to the number of bits that can be transferred simultaneously at any given time.

Question 16

Usually, how wide are buses?

Answer 16

8, 16, 32, or 64 wires wide.

Question 17

What is the data bus?

Answer 17

A bidirectional bus used to transport data and instructions between components.

Question 18

What is the control bus?

What does it coordinate?

Answer 18

A bidirectional bus used to transmit control signals between internal and external components.

It coordinates the use of the address and data buses and provides status information between system components.

Question 19

What is the address bus used for?

What is the width of the address bus proportional to?

Answer 19

Used to transmit the memory address specifying where data is to be sent from or retrieved from.

The number of addressable memory locations.

Question 20

Name 3 control signals

Answer 20

• Bus request: shows that a device is requesting the use of the data bus
• Bus grant: shows that the CPU has granted access to the data bus
• Memory write: data is written into the addressed location using this bus
• Memory read: data is read from a specific location to be placed onto the data bus,
• Interrupt request: shows that a device is requesting access to the CPU
• Clock: used to synchronise operations

Question 21

What does adding a wire to the address bus do to the number of addressable locations?

Answer 21

It doubles the number of addressable locations.

Question 22

What does the Bus Request indicate?

Answer 22

Indicates a device is requesting access to the data bus.

Question 23

What does Bus Grant indicate?

Answer 23

Indicates the CPU has granted access to the data bus.

Question 24

What does memory write do?

Answer 24

Causes the data on the data bus to be written into the addressed location.

Question 25

What does memory read do?

Answer 25

Causes the data from the addressed location to be placed onto the data bus.

Question 26

What does the interrupt request control signal indicate?

Answer 26

Indicates a device is requesting access to the CPU.

Question 27

What is the clock control signal used for?

Answer 27

Used to synchronise instructions.

Question 28

What is assembly language?

Answer 28

A programming language where mnemonics are used to represent instructions.

Therefore, it is a simplified way of representing machine code.

Question 29

What is opcode?

Answer 29

Opcode is used to determine the type of instruction and what hardware to use to execute it.

Question 30

What is the operand?

Answer 30

The operand contains the data or the address of the data upon which the operation is to be performed.

Question 31

What is the FDE cycle?

Answer 31

The sequence of operations that are completed in order to execute an instruction.

Question 32

What occurs during the fetch phase of the FDE cycle?

Answer 32

• Address from the PC is copied to the MAR
• Instruction held at that address is copied to MDR by the data bus
• Simultaneously, the contents of the PC are increased by 1
• The value held in the MDR is copied to the CIR

Question 33

What occurs during the decode phase of the FDE cycle?

Answer 33

The contents of the CIR are split into operand and opcode.

Question 34

What occurs during the execute phase of the FDE cycle?

Answer 34

The opcode is executed on the data.

Question 35

What is the clock speed?

Answer 35

The number of clock cycles completed per second.

Question 36

What is clock speed determined by?

Answer 36

The system clock.

Question 37

What is the system clock?

Answer 37

It is the electronic device which generates signals, switching between 0 and 1. All processor activities begin on a clock pulse, and each CPU operation starts as the clock changes from 0 to 1.

Question 38

What is a core?

Answer 38

A core is an independent processor that is able to run its own fetch-execute cycle.

Question 39

How does having multiple cores affect a computer?

Explain further, using a dual core computer as an example.

Answer 39

A computer with multiple cores can complete more than one fetch-execute cycle at any given time.

A computer with dual cores can theoretically complete tasks twice as fast as a computer with a single core.

Question 40

Are all programs able to utilise multiple cores efficiently? Why?

Answer 40

No.

Not all programs are able to utilise multiple cores efficiently as they have not been designed to do so, so this is not always possible.

Question 41

What is cache memory?

Answer 41

The CPU’s onboard memory, which can be accessed a lot faster than main memory.

Question 42

What makes cache memory fast?

Answer 42

Instructions fetched from main memory are copied to the cache, so if required again, they can be quickly accessed.

Question 43

What happens as cache memory fills up?

Answer 43

Unused instructions are replaced.

Question 44

What are the levels of cache, how do they differ?

Answer 44

Level 1 Cache –> Fastest Memory cells with small capacity.

Level 3 Cache –> Much larger and slower memory cell.

Question 45

What is Von Neumann architecture?

Answer 45

Architecture in which there is a single shared memory and shared data bus for both data and instructions.

It includes all the basic components of the computer and processor. It is built on the stored program concept.

Question 46

What is Harvard architecture?

Answer 46

Architecture in which there is two physically separate memory and data buses for data and instructions.

Question 47

What are the advantages of Von Neumann Architecture?

Answer 47

Cheaper to develop as the control unit is easier to design.

Programs can be optimised in size.

Question 48

What are the advantages of Harvard Architecture?

Answer 48

Quicker execution as data and instructions can be fetched in parallel.

Memories can be different sizes, which can make more efficient use of space.

Question 49

What is contemporary processing?

Answer 49

Processing in which Von Neumann architecture is used when working with data and instructions in main memory, but Harvard architecture is used to divide cache into instruction cache and data cache.