✅1.1.1 Structure and function of the processor

Question 1

What does the control unit do?

Answer 1

1. Coordinates all activities of the CPU
2. Directs the flow of data between the CPU and other devices
3. Accepts the next instruction, decodes it, handles its execution, and stores the resulting data back in memory or registers

Question 2

What does the Accumulator do?

Answer 2

1. A register in the processor that stores data and control information
2. The results of calculations carried out by the ALU can be temporarily stored here

Question 3

What does the Program Counter do?

Answer 3

A register in the processor that holds the address of the next instruction to be executed

Question 4

What does the Arithmetic Logic Unit do?

Answer 4

1. Performs arithmetic and logical operations on data
2. It can perform ADD, SUBTRACT, MULTIPLY, DIVIDE on fixed and floating point numbers
3. Performs shift operations, shifting bits to the left or right within a register
4. Carries out Boolean logic operations, comparing two values and using operators such as AND, OR, NOT, XOR

Question 5

What does the Memory Address Register do?

Answer 5

1. Holds the address of the memory location from which data or an instruction is to be fetched or to which the data is to be written
2. Sends these address to memory down the address bus

Question 6

What does the Memory Data Register do?

Answer 6

1. Used to temporarily store the data which us read from or written to memory.
2. Gateway to the processor
3. All data to and from memory must travel down the data bus and pass through the MDR.

Question 7

What does the Current Instruction Register do?

Answer 7

1. Holds the current instruction being executed
2. The contents of the MDR are copied to the CIR if it is an instruction.
3. Contains the opcode and operand(s) of the current instruction.

Question 8

What happens during the fetch stage of the FDE cycle?

Answer 8

1. The address of the next instruction is copied from the program counter (PC) to the memory address register (MAR).
2. The instruction held at that address is copied to the memory data register (MDR). Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction.
3. The contents of the MDR are copied to the current instruction register (CIR).

Question 9

What happens during the decode stage of the FDE cycle?

Answer 9

The instruction held in the CIR is decoded. The instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it. The operand holds either:
- the address of the data to be used with the operation, which is then copied to the MAR, or
- the actual data to be operated on, which will be copied to the MDR
- the data to be operated on may be passed to the ALU/accumulator

Question 10

What happens during the execute stage of the FDE cycle?

Answer 10

The appropriate instruction/opcode is carried out on the operand

Question 11

What does the data bus do?

Answer 11

Stores data being sent to and from the CPU and RAM

Question 12

What does the address bus do?

Answer 12

Stores the address of data being sent to and from the CPU and RAM

Question 13

What does the control bus do?

Answer 13

Sends signals to determine whether the other buses are in read or write mode

Question 14

What are registers?

Answer 14

Small memory cells that operate at high speeds.
They are used to temporarily store data and all arithmetic, logical and shift operations occur in these registers.

Question 15

What is a bus?

Answer 15

A set of parallel wires connecting two or more components together

Question 16

What is a system bus?

Answer 16

The collection of the data bus, address bus, and control bus is called the system bus.

Question 17

What is the width of a bus?

Answer 17

The number of parallel wires it has

Question 18

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

Answer 18

It doubles the number of addressable locations

Question 19

What does Bus Request indicate?

Answer 19

Indicates a device is requesting access to the data bus

Question 20

What does Bus Grant indicate?

Answer 20

Indicates the CPU has granted access to the data bus

Question 21

What does memory write do?

Answer 21

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

Question 22

What does memory read do?

Answer 22

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

Question 23

What does the interrupt request control signal indicate?

Answer 23

Indicates that a device is requesting access to the CPU

Question 24

What is the clock control signal used for?

Answer 24

It is used to synchronise instructions

Question 25

What is Assembly Language?

Answer 25

Assembly Language is a programming language where mnemonics are used to represent instructions

Question 26

What is opcode?

Answer 26

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

Question 27

What is operand?

Answer 27

The operand is the address of where the operation is performed

Question 28

What is clock speed?

Answer 28

The number of clock cycles completed per second

Question 29

What is cache memory?

Answer 29

Temporary storage of data and instructions being read from and written to the main memory, used for quick access

Question 30

What are 4 features of Harvard architecture?

Answer 30

1. Instructions and data stored in separate memory units 2. Each has its own bus 3. Reading and writing data can be done at the same time as fetching an instruction 4. Used by RISC processors

Question 31

What are 5 features of Von Neumann architecture?

Answer 31

1. Shared memory space for instructions and data. 2. Instructions and data are stored in the same format. 3. A single control unit or processor follows a linear fetch, decode, execute cycle. 4. One instruction processed at a time 5. Registers are used for fast access to instructions and data

Question 32

What is contemporary processing?

Answer 32

Processing in which Von Neumann architecture is used for main memory. Cache uses Harvard architecture, divided into instruction cache and data cache

Question 33

What are 2 advantages of a monitoring system for patients' vital signs having its operating system stored in ROM? (2 Marks)

Answer 33

1. ROM is quick to start up so the system can be started up quickly (in an emergency). 2. ROM cannot be altered so there is no chance of the OS being accidentally or maliciously changed (on what is a safety critical system).

Question 34

What happens to the contents of RAM and ROM when power to a monitoring system for patients' vital signs is removed? (2 Marks)

Answer 34

The contents of RAM are lost, whereas the contents of ROM remain the same.

Question 35

Explain why flash storage would be more appropriate than a magnetic hard drive for a device which estimates the calories burnt by a user. (3 Marks)

Answer 35

1) The device is likely to be small so Flash memory would be best as it has no moving parts, requiring much less space than hard drives which require enough space for their moving parts. OR 2) The device is likely to undergo lots of sudden movements which hard drives can be susceptible to damage if moved quickly due to the head coming in contact with the platter. Whereas flash memory has no moving parts so is not affected.

Question 36

Explain why a GPU is more suitable than a CPU for a new video games console in which the console will use a modified version of an operating system called Linux. (3 Marks)

Answer 36

CPUs are general purpose processors whereas GPUs are specifically for graphics so are likely to have built in circuitry for common graphics operations.

Question 37

A company releases a utility called utility software. The utility creates a virtual storage drive from an area of the computers RAM. Give one advantage of using RAM as storage in this way. (1 Mark)

Answer 37

Faster read/write speed than secondary storage media.

Question 38

Why is it necessary for a a utility to periodically copy information in the RAM to secondary storage, such as a hard disk? (2 Marks)

Answer 38

RAM is volatile meaning it loses its information when power is lost so must be copied to secondary storage in case of unexpected power failure.

Question 39

How many wires wide are buses usually?

Answer 39

8, 16, 32, or 64 wires wide

Question 40

What are the properties of Level 1 cash?

Answer 40

Very fast memory cells with a small capacity. (2-64KB)

Question 41

What are the properties of Level 2 cache?

Answer 41

Relatively fast memory cell, with a medium sized capacity. (256KB-2MB)

Question 42

What are the properties of Level 3 cache?

Answer 42

Much larger and slower memory cell.