Section 5 Chapter 26 - The processor

Question 1

Components of the processor (5)

Answer 1

• ALU
• Control unit
• System clock
• General purpose registers
• Dedicated registers

Question 2

System clock

Answer 2

Switches between 1 and 0 millions of times per second. Each CPU operation starts as the clock changes from 0 to 1

Question 3

General purpose register

Answer 3

A very fast piece of memory where arithmetic and logical operations take place.

Question 4

Accumulator

Answer 4

A general purpose register where the processor only has one

Question 5

Dedicated registers (5)

Answer 5

• Program counter (PC)
• Current Instruction Register (CIR)
• Memory address register (MAR)
• Memory buffer register (MBR)
• Status register (SR)

Question 6

Program Counter

Answer 6

Holds the address of the next instruction to be executed

Question 7

Current Instruction Register

Answer 7

Holds the current instruction being executed

Question 8

Memory address register

Answer 8

Holds the address of the memory location from which data is to be fetched or written

Question 9

Memory buffer register

Answer 9

Used to temporarily store the data read or written from memory

Question 10

Status register

Answer 10

Contains bits that are true depending on the result of an instruction, for instance if an overflow occurs

Question 11

Factors affecting processor performance (6)

Answer 11

• Number of cores
• Amount and type of cache
• Clock speed
• Word length
• Address bus width
• Data bus width

Question 12

Why dual core processors are not always twice as fast

Answer 12

The software may not be able to take advantage of both cores

Question 13

Cache

Answer 13

A small expensive and very high speed memory located inside or near the CPU

Question 14

What cache stores

Answer 14

When an instruction is fetched from main memory it is stored in cache in case it is needed again

Question 15

The levels of memory (by speed)

Answer 15

Registers
L1 cache
L2 cache
L3 cache
RAM

Question 16

ALU

Answer 16

Arithmetic Logic Unit

Performs arithmetic operations, for example adding or subtracting as well as logical operations for instance AND or XOR

Question 17

CU

Answer 17

Control Unit
Controls and coordinates the activities of the CPU. It accepts an instruction, breaks it into sequential steps and then manages its execution

Question 18

Dedicated register

Answer 18

A very fast piece of memory that has a specific task within the fetch-decode-execute cycle

Question 19

The fetch-decode-execute cycle

Answer 19

1 - The address of the next instruction is copied from the PC to the MAR
2 - The instruction held at that address is copied to the MBR and the contents of the PC is incremented to hold the address of the next instruction
3 - The contents of the MBR are copied to the CIR
4 - The instruction in the CIR is decoded
5 - The instruction is executed

Question 20

Why multi core processors are faster

Answer 20

Each processor can process a different instruction with its own fetch-execute cycle, all simultaneously

Question 21

How clock speed affects the processor performance

Answer 21

High clock speed means more instructions can be carried out per second

Question 22

How word length affects processor performance

Answer 22

A higher word length means that the processor can process more bits simultaneously, meaning a higher throughput of bits per second

Question 23

How address bus width affects processor performance

Answer 23

If the address bus width is not large enough to hold all the bits necessary to address all places in memory then the address will need to be sent in two parts, which will slow down the overall speed of processing

Question 24

How data bus width affects processor performance

Answer 24

The width of the data bus is the amount of bits that can be transferred simultaneously and thus a higher width means that more bits can be sent to or from the processor in the same amount of time