Section 1 - Components Of A Computer

Question 1

What is another name for the CPU?

Answer 1

Processor

Question 2

What are the 4 main components of the CPU?

Answer 2

1) Control Unit
2) Buses
3) Arithmetic Logic Unit
4) Dedicated Registers

Question 3

What is the CPU’s function?

Answer 3

To execute instructions

Question 4

What does the Control Unit Do? (3 points)

Answer 4

1) Controls and co-ordinates the activities of the CPU
2) Directs the flow of data between the CPU and other devices
3) Accepts the next instruction and decodes it into several steps such as fetching addresses and data from memory, manages its execution and stores the resulting data back in memory or registers

Question 5

What is a bus?

Answer 5

A set of parallel wires connecting two or more components of a computer

Question 6

How many lines typically does a bus consist of?

Answer 6

8, 16, 32, or 64 lines

Question 7

What are the data, address, and control bus collectively known as?

Answer 7

The system bus

Question 8

How are the system buses used collectively with the CPU and the main memory? (3 points)

Answer 8

1) When the CPU wishes to access a particular main memory location, it sends this address to memory on the address bus
2) The data in that location is then returned to the CPU on the data bus
3) Control signals are sent along the control bus

Question 9

What are the main components the system buses connect?

Answer 9

1) Processor
2) Memory
3) Input/Output controllers

Question 10

Each bus is a “shared transmission medium”, what does this mean?

Answer 10

Only one device can transmit along a bus at any one time

Question 11

What directions can the control signals travel between the processor, memory, and I/O controllers?

Answer 11

Both

Question 12

What directions can the data signals travel between the processor, memory, and I/O controllers?

Answer 12

Both

Question 13

What directions can the address signals travel between the processor, memory, and I/O controllers?

Answer 13

Only one way; the processor sends the address of an instruction, or of data to be stored or retrieved, TO memory, or TO and I/O controller

Question 14

Why is the control bus necessary?

Answer 14

The data and address buses are shared by all the components of a system, therefore control lines must be provided to make sure that access to and use of data does not lead to conflict

Question 14

What is the purpose of the control bus?

Answer 14

To transmit command, timing, and specific status information between system components

Question 14

What is the purpose of the data bus?

Answer 14

To move data and instructions between system components

Question 15

What are the 6 control lines and purpose?

Answer 15

1) Bus request - Indicates that a device is requesting the use of the data bus
2) Bus grant - Indicates that the CPU has granted access to the data bus
3) Memory Write - Causes data on the data bus to be written into the addressed location
4) Memory Read - Causes data from the addressed location to be placed on the data bus
5) Interrupt request - Indicates that a device is requesting access to the CPU
6) Clock - Used to synchronise operations

Question 16

What is a word?

Answer 16

Units that memory is divided up internally into, which are a fixed size group of digits handled as units by the processor

Question 16

Typically, how many bits are words?

Answer 16

8, 16, 32, or 64 bits

Question 16

Why would word size vary?

Answer 16

Different types of processors have different word sizes

Question 16

What does the address bus do?

Answer 16

Transmits the memory address of words that are used as operands in program instructions, so that the data can be retrieved and sent back to the processor.
However, when an instruction has been performed and the result is to be stored at a particular memory location, it is transmitted via the data bus.

Question 17

What does the ALU do? Give 3 examples.

Answer 17

The ALU performs arithmetic and logic operations on the data.
1) ARITHMETIC - It can perform instructions such as ADD, SUBTRACT, MULTIPLY, or DIVIDE on fixed or floating point numbers
2) SHIFT - It can also perform shift operations, shifting bits to the left or right in a register
3) LOGIC - It can carry out Boolean logic operations, comparing two values using operators such as AND, OR, NOT, or XOR

Question 18

What is a register?

Answer 18

A special memory cell that operates at a very high speed

Question 19

Where do all arithmetic, logical, and shift operations take place?

Answer 19

Registers

Question 19

Typically, how many registers are in the CPU?

Answer 19

16

Question 20

What is the accumulator?

Answer 20

A register, or a memory location used to store the intermediate results of arithmetic and logical operations.

Question 20

Why do some special purpose computers still use a single accumulator?

Answer 20

In order to simplify the design

Question 21

What does the accumulator do?

Answer 21

Takes the place of the general purpose registers.
For simplicity, we assume that all calculations take place here

Question 22

What does the PC do?

Answer 22

Holds the address of the next instruction to be executed.
This may be the next instruction in a sequence of instructions, or if the current instruction is a branch or jump instruction, then it may the the instruction to jump to (copied from the CIR to the PC)

Question 22

What is operand?

Answer 22

Part of the instruction which holds either:
- The address of the data to be used with the operation, which is then copied to the MAR
- The actual data to be operated on, which will be copied to the MDR
- The data to be operated may be passes on to the ALU/accumulator

Question 22

What is opcode?

Answer 22

Part of the instruction that is used to determine the type of instruction and what hardware to use to execute it

Question 22

What 2 things are instructions divided into?

Answer 22

Operand and Opcode

Question 23

What does the CIR do?

Answer 23

Holds the current instruction being executed

Question 23

What does the MAR do?

Answer 23

Holds the address of the memory location from which data (or an instruction) is to be fetched or to which data is written

Question 23

What does the MDR do?

Answer 23

Used to temporarily store the data read from or written to memory (also can be known as the memory buffer register)

Question 24

What are the 3 phases a sequence of operations involved in executing an instruction divided up into?

Answer 24

Fetching
Decoding
Executing
This cycle repeats over and over as each instruction of the program is executed

Question 25

What happens in the fetch phase of the FDE cycle?

Answer 25

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 MDR. Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction
3) The contents of the MDR are copied to the CIR

Question 25

What happens in the decode phase of the FDE cycle?

Answer 25

4) The instruction held in the CIR is decoded. The instruction is split up into opcode and operand.

Question 26

What happens in the execute phase of the FDE cycle?

Answer 26

5) The appropriate instruction/opcode is then performed on the operand