2.1 The CPU + Fetch-Decode-Execute

Question 1

What is the CPU?

Answer 1

The internal hardware component that is responsible for processing data and executing the instructions of programs.

Question 2

What is the ALU?

And what does it do?

Answer 2

The arithmetic logic unit.

Performs arithmetic and logical calculations.

Question 3

What is the CU?

And what does it do?

Answer 3

The control Unit organises the order of program instructions.

Question 4

Name four processes the Control Unit completes:

Answer 4

Sends control signals to enable data to be read and written.
Decodes instructions to determine what needs to be done.
Organises sequence of micro-operations
Uses control signals to determine which operation the ALU will carry out.

Question 5

What is the Clock?

Answer 5

The system clock generates a regular pulse to synchronise operations.

Question 6

What is a clock low?

Answer 6

0

Question 7

What is a clock high?

Answer 7

1

Question 8

What is a rising edge?

Answer 8

Low to high

Question 9

What is a falling edge?

Answer 9

high to low

Question 10

What is a clock period?

Answer 10

time between two rising edges

Question 11

What is a clock cycle?

Answer 11

One clock period

Question 12

Equation for clock rate:

Answer 12

Clock frequency (a.k.a. rate or speed) = 1 / clock period

Question 13

What are registers?

Answer 13

Locations of computer memory that provide fast access.

Question 14

What are general purpose registers?

Answer 14

Temporary storage for operation results that need to be accessed again

Question 15

What are dedicated registers?

Answer 15

Registers for a specific purpose.

Question 16

Name some dedicated registers

Answer 16

Program Counter
Current Instruction Register
Status Register
Memory Address Register
Memory Buffer Register (a.k.a. Memory Data Register)
Accumulator

Question 17

What is PC? And what does it do?

Answer 17

The program counter holds the address of the next instruction to be executed.

Question 18

What is the CIR? And what does it do

Answer 18

Current Instruction Register, holds the current instruction.

WOW

Question 19

What is the SR? And what does it do?

Answer 19

The Status Register stores information about the result of the last instruction. To indicate if an error or exception has occurred to help disable interrupts.

Question 20

What is an error or exception?

Answer 20

Result of a calculation that requires further action

Question 21

What is an interrupt?

Answer 21

Event outside program that requires attention of processor

Question 22

What is the MAR? And what does it do?

Answer 22

Temporarily holds the address of the memory location processor needs to access.

Question 23

What is the Memory Buffer Register and what does it do?

Answer 23

The MBR temporarily holds the data that are read from or written to main memory a.k.a. Memory Data Register (MDR)

Question 24

What is the accumulator?

Answer 24

Stores the results of any calculation processed by the ALU

Question 25

What is the Fetch-Decode-Execute Cycle?

Answer 25

A sequence of steps behind every operation carried out in the computer.

Question 26

What has to occur before the FDE?

Answer 26

The program instructions have to be translated into machine code.
And the program instructions have to be loaded from secondary storage into main memory.

Question 27

What happens in the Fetch Part?

Answer 27

• (PC) Program Counter provides address of next instruction
• This address is copied to memory address register (MAR)
• Address sent to Main Memory along address bus.
• Control Unit (CU) sends a signal along control bus.
• The content stored at the address is sent along data bus to the Memory Data Register (MDR).
• Data is copied to Current Instruction Register (CIR)

Question 28

What happens in the Decode Part?

Answer 28

Control Unit decodes the instruction of CIR

Question 29

What happens in the Execute part?

Answer 29

Instruction is executed in the exact sequence of operations necessary for that instruction.

Question 30

What occurs at the end of the cycle?

Answer 30

At the end of a cycle the processor checks the status register for an error or exception or interrupt. Before starting the next cycle.

Question 31

What is a data bus?

Answer 31

Sends data from the registers to the RAM.

Question 32

What is command line?

Answer 32

Text interface on your computer.

Question 33

What is different between Command Line and GUI?

Answer 33

GUI lets a user interact with the device/system with the help of graphical elements, like windows, menus, icons, etc.
The CLI, on the other hand, lets a user interact with their device/system with the help of various commands.
Some OS provide their users with only CLI, while some offer both CLI and GUI.