1.1 The central processing unit

Question 1

central processing unit

Answer 1

CPU

fetches, decodes and executes instructions

Question 2

list of components/registers

Answer 2

Registers:

• memory address register (MAR)
• memory data register (MDR)
• program counter (PC)
• accumulator (ACC)
• arithmetic logic unit (ALU)
• control unit (CU)
• cache
• decoder
• clock
• buses

Question 3

CU

Answer 3

control unit

controls all the other components of the CPU (by sending signals to control the movement of data)

contains the decoder

Question 4

decoder

Answer 4

interprets program instructions and tells the ALU what operations to carry out

located inside the control unit

Question 5

clock

Answer 5

controls the rate at which program instructions are carried out

sends control electrical signals at regular intervals, called cycles

Question 6

ALU

Answer 6

arithmetic logic unit

performs arithmetic and logical operations to carry out program instructions

Question 7

buses

Answer 7

electrical conductors that carry electrical signals between components in the CPU

and between the CPU and other components on the motherboard

Question 8

(function of) registers

Answer 8

memory locations

some perform special functions in the fetch-decode-execute cycle

Question 9

cache

Answer 9

very fast random access memory (RAM)

contains frequently used instructions and data that can be accessed without having to go to the main memory

Question 10

clock cycle

Answer 10

the CPU carries out 1 program instruction each clock cycle

Question 11

clock speed

Answer 11

measured in GHz

1 GHz is 10[9] cycles a second

1 GHz is a billion cycles a second

affects performance of the CPU

Question 12

average clock speed of most home computers

Answer 12

between 1 and 3 GHz

Question 13

Matthew has bought a laptop with a 2.2 GHz central processing unit (CPU)

a) state the purpose of the CPU [1]
b) describe what is meant by a 2.2 GHz CPU. [2]

Answer 13

a) the function of the CPU is to fetch and execute program instructions stored in memory
b) a 2.2 GHz CPU has a lcok speed of 2.2 GHz.

this is the number of instructions that can be processed per second

a 2.2 GHz processor can complete 2.2 billion processing cycles a second

Question 14

List three components of a CPU [3]

Answer 14

• control unit
• arithmetic logic unit
• cache
• registers
• clock

Question 15

Explain why a computer with a 2.2 GHz CPU might be considered preferable to one with a 1 GHz CPU [2]

Answer 15

the clock sends out electrical control signals at regular intervals

the rate of the pulses affects the execution of instructions by the CPU

a CPU with a clock that sends out 2.2 billion cycles per second can execute instructions faster than one with only one billion cycles a second

(this makes the computer run faster)