Computer Architecture

Question 1

What is the role of the CPU

Answer 1

• The CPU processes instructions and data that are input into the computer so that the result can be output.
• Fetch decode and execute

Question 2

Define Microprocessor/ CPU

Answer 2

A microprocessor is a type of integrated circuit that is contained on a single chip

Question 3

Function of the Address Bus (3)

Answer 3

• Transports an address
• Of the next item to be fetched
• Data travels one way (unidirectional)

Question 4

Function of the Data Bus (3)

Answer 4

-Transports data
- That is currently being processed // that will be / has been processed
- Data can travel in both directions (bidirectional)

Question 5

Function of the Control Bus (3)

Answer 5

• Transports signals
• Controls the actions of the CPU
• Can be either Unidirectional or Bidirectional

Question 6

What is a bus?

Answer 6

A bus is a set of parallel wires through which data/signals are transmitted from one component to another

Question 7

Function of the Arithmetic logic unit (ALU)

Answer 7

Performs arithmetic operations and logical decisions

Question 8

Function of the Control Unit (CU)

Answer 8

• Coordinates how data moves around the CPU by sending a signal to control the movement of the data
• Decodes the instructions fetched from memory

Question 9

Function of Registers

Answer 9

Extremely small, extremely fast memory located in the CPU and hold small amounts of data needed as part of the fetch-execute cycle

Question 10

What are the 5 main registers of the CPU?

Answer 10

• The Program Counter (PC)
• The Memory Address Register (MAR)
• The Memory Data Register (MDR)
• The Accumulator (ACC)
• Current Instruction Register (CIR)

Question 11

Function of the Program Counter (PC)

Answer 11

• Holds the memory address of the next instructions to be executed
• Increments by 1 as the fetch-decode-execute cycle runs

Question 12

Function of the Memory Address Register (MAR)

Answer 12

• Holds the memory address of where data or instructions are to be fetched from memory

Question 13

Function of the Memory Data Register (MDR)

Answer 13

• Stores the data or instruction which has been fetched from memory

Question 14

Function of the Accumulator (ACC)

Answer 14

• Stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU)

Question 15

Function of the Current Instruction Register (CIR)

Answer 15

• Stores the instruction the CPU is currently decoding or executing

Question 16

Describe the role of the control unit, the control bus, the data bus and the address bus when fetching an instruction from memory (4)

Answer 16

• The address of memory (holding instruction) is placed on the address bus (1)
• The control unit sends a signal (1) on the control bus (to start a read operation) (1)
• The instruction is/the contents of the memory are placed on the data bus (1)

Question 17

What is the FDE cycle?

Answer 17

• The Fetch-Decode-Execute Cycle is the cycle that the central processing unit (CPU) runs through billions of times per second to make a computer work

Question 18

Describe the process of the fetch stage

Answer 18

• During the fetch stage of the cycle, the program counter holds the address of the next instruction to be fetched from memory
• The address of the next instruction or data to be fetched is copied into the memory address register (MAR)
• The address of the instruction or data is then sent along the address bus and awaits a signal from the control bus
• The signal sent along the control bus is sent from the control unit (CU) to the main memory
• The data or instructions received from main memory is fetched to the memory data register (MDR) via the data bus
• A copy of the instruction or data is stored in the current instruction register (CIR)
• The program counter (PC) increments by 1 so it is pointing to the next instruction to be executed

Question 19

Describe the process of the decode stage

Answer 19

During the decode stage of the cycle, the CPU needs to work out what is required from the instruction.

Question 20

Opcode

Answer 20

What the instruction is

Question 21

Oprand

Answer 21

• What to do the instruction to
• This could be either data or an address where the data is stored

Question 22

Describe the process of the execute stage and give examples.

Answer 22

• During the execute stage of the cycle, the CPU will carry out the instruction that was fetched
• Performing a calculation
• Storing a result or data back in main memory (RAM)
• Going to main memory to fetch data from a different location

Question 23

What three characteristics affect the CPU speed

Answer 23

• Clock Speed
• Cache Size
• Number of Cores

Question 24

Clock Speed

Answer 24

• The clock speed is measured in Hertz (Hz) and is the number of fetch-decode-execute cycles that can take place in 1 second
• The faster the clock speed, the more instructions can be fetched and executed per second

Question 25

Cache Size

Answer 25

- Cache is very small, very fast memory on or close to the CPU - The larger the cache size, the more frequently used instructions or data can be stored - This results in the CPU having to complete fewer fetch cycles from memory (RAM), speeding up the performance

Question 26

Number of Cores

Answer 26

- A core works like it is its own CPU - Multiple core processors mean they have multiple separate processing units that can fetch, decode and execute instructions at the same time

Question 27

Explain why having a dual core processor might improve the performance of the computer (2)

Answer 27

- The computer with the dual core processor has two cores/double the amount of cores [1] - Parallel processing can take place [1] - Each core can execute a separate instruction at the same time [1] - Each core can process instructions independently of each other [1]

Question 28

Describe a CPU instruction set

Answer 28

An instruction set is a list of all the commands that can be processed by a CPU, and the commands are machine code

Question 29

What is an embedded system?

Answer 29

An embedded system is a computer system which is used to perform a dedicated function, inside a larger mechanical unit

Question 30

Examples of embedded systems

Answer 30

-Heating thermostats -Hospital equipment -Washing machines -Dishwashers -Coffee machines -Satellite navigation systems -Factory equipment -Security systems -Traffic lights

Question 31

Properties of an embedded system

Answer 31

-They are small in size -They use less power than a general-purpose computer -They have a lower cost