Hardware - Computer Architecture

Question 1

what is the role of the CPU in a computer

Answer 1

continuously processes instructions and data that are inputted by repeatedly carrying out the fetch-execute cycle in order to output a result

Question 2

what is meant by a microprocessor

Answer 2

a type of integrated circuit on a single chip that processes instruction

Question 3

what are the 5 key elements of Von Neumann architecture:

Answer 3

• data + instruction are both stored as binary digits
• data + instructions both stored in primary memory
• instructions are fetched one at a time and in order (sequentially)
• cycle continues until no more instructions are available

Question 4

what components are in the CPU

Answer 4

• ALU (Arithmetic Logic Unit)
• Control Unit
• Clock
• Registers
• Address, Data and Control Buses

Question 5

what is the function of the ALU

Answer 5

• carries out mathematical + logical operations on data, including:
  
  • Mathematical = ADD, SUBSTRACT …
  • binary shifts
  • Logical = AND, OR , NOT
  • compares values held in registers

Question 6

what is the function of the accumulator (ACC)

Answer 6

• register in which results of operations carried out in the ALU are ** temporarily stored** for quicker retrieval
• one of several general-purpose registers

Question 7

what components are in the ALU units

Answer 7

• MDR
• ACC

Question 8

function of the CU

Answer 8

• coordinates all of the CPU’s actions in the fetch-decode-execute cycle and decodes instruction
• sends + receives control signals to fetch + write data

Question 9

what is the function of the Clock

Answer 9

• Electronic unit that synchronises + regulates the speed and timings of all signals + computer functions

Question 10

what is the function of Registers

Answer 10

• very small, very fast memory locations
• registers built into the CPU chip to temporarily store memory addresses, instructions or data
• used in the fetch-decode-execute cycle for specific purposes

Question 11

what does PC stand for

Answer 11

Program Counter

Question 12

what is the function of the Program Counter

Answer 12

• is a register that golds the memory address of the next instruction to be processed

Question 13

what is MAR

Answer 13

Memory Address Register

Question 14

what is the function of the MAR

Answer 14

• holds address (location in memory) of the current instruction / piece of data to be fetched or stored

Question 15

to which component does the MAR send the address to

Answer 15

to the main memory down the *address bus**

Question 16

what does MDR stand for

Answer 16

Memory Data Register

Question 17

what is the function of the MDR

Answer 17

• temporarily holds data / program instruction when it is:
  
  • fetched from memory OR
  • data the is waiting to be written to memory

Question 18

what must all data do when travelling to and from the main memory

Answer 18

travel down the Data Bus and pass through the MDR

Question 19

what does CIR stand for

Answer 19

Current Instruction Register

Question 20

what is the function of the CIR

Answer 20

• holds the instruction hat is currently being executed
• if MDR contains an instruction, this will be copied to the CIR

Question 21

what are the 3 types of buses

Answer 21

• address
• data
• control

Question 22

what is the purpose of an address bus

Answer 22

Unidirectional - carries memory addresses that identify where data is being read from or written to

Question 23

what is the purpose of an data bus

Answer 23

Bidirectional - carries the binary 1s and 0s that make up the actual information being transmitted around the CPU / computer

Question 24

what is the purpose of an control bus

Answer 24

Bidirectional - carries command + control signals to and from one component to another in the CPU

Question 25

what is the fetch-decode-execute cycle

Answer 25

- **continuous repetitive cycle** - every CPU instruction is **fetched from memory** - is then **decoded** by the **Control Unit** to find out what to do with it - instruction is then **executed**

Question 26

each operation carried out within the fetch-decode-execute cycle is regulated by what

Answer 26

a 'tick' or **cycle** of the **CPU clock**

Question 27

describe in detail the stages of the fetch-decode-execute cycle

Answer 27

FETCH Stage: 1. The memory **address** held in the **program counter** is **copied** into the **MAR** 2. **increment PC** so that **address** is now for the **next instruction** can be fetched 3. processer sends **signal** to address in **MAR** to be sent along **address bus** to *main memory** --> where it **waits** to receive a **signal** from the **control bus** 4. CU sends a **read signal** along **control bus** to main memory 5. contents at address within memory is sent along the **data bus** and to the **MDR** 6. data received in MDR is **copied to Current Instruction Register** 7. data in CIR is **decoded + executed** --> results of processing are **stored** in the **ACC** 8. repeats

Question 28

what components are in the CU

Answer 28

- PC - CIR - MAR

Question 29

describe the steps within the Decode stage

Answer 29

- instruction held in **CIR** is inspected and **decoded** to work out what needs to be done

Question 30

describe the steps within the Execute stage

Answer 30

- send **address** from CIR to **MAR** - send data down the **address bus** to **main memory** for it to **read** --> **CU** sends **read signal** along **control bus** to main memory - address sent along **data bus** to **MDR** - contents of MDR are **copied** to the **ACC** to be carried out