Components of a Computer

Question 1

What is the Purpose of the Address Bus?

Answer 1

The address bus carries memory addresses of data for retrieval to the main memory.

Question 2

What is Virtual Memory and what are its Disadvantages?

Answer 2

Virtual Memory is used when data needs to be added to RAM, but it is full. In this case data not being currently used will be offloaded to the secondary storage to free up space in RAM.

This process is very inefficient - often leading to “disk thrashing” when the system is spending most of it’s time swapping data in and out of RAM.

Question 3

What is the Accumulator?

Answer 3

The Accumulator (ACC) stores the results of all operations carried out in the Arithmetic Logic Unit, and acts as a buffer between the CPU and RAM.

Question 4

What is the relationship between the address bus and the size of the system memory.

Answer 4

The address bus transmits memory locations. Since a larger memory means a larger range of memory addresses, more memory means a larger address bus is required.

Question 5

What is the Program Counter?

Answer 5

The Program Counter holds the address of the next instruction to be executed.

Question 6

What are the jobs of the Control Unit?

Answer 6

• Co-coordinating access to the system memory and buses.

- Decoding Instructions.

Question 7

What is Pipelining?

Answer 7

Pipelining is a technique used by CPUs to allow multiple instructions to be processed at the same time by ensuring that there is always one instruction being fetched, decoded and executed.
This allows instructions to move through the processing stages like an assembly line.

Question 8

What are Registers?

Answer 8

Registers are high speed temporary data storage locations inside the CPU.

Question 9

What is the Arithmetic Logic Unit?

Answer 9

The Arithmetic Logic Unit performs arithmetic and logical operations on the data stored in the registers.

Question 10

What is Cache Memory?

Answer 10

Cache is a small high speed storage location inside the CPU, used to temporarily store recently fetched instructions, in case they are required again.
Fetching these instructions from cache is far faster than fetching them from RAM again.

There are three different levels of cache:

• Level 1: Extremely Fast but Small
• Level 2: Fairly Fast and Medium-Sized
• Level 3: Slower but Larger

Question 11

What is RAM?

Answer 11

RAM is a temporary storage location used to hold data and instructions currently in use.

Question 12

What Factors Affect CPU Performance?

Answer 12

• Clock Speed
• Numbers of Cores
• The Level of Cache Memory

Question 13

What is the Current Instruction Register?

Answer 13

The Current Instruction Register holds the instruction currently being executed.

Question 14

What is the Memory Address Register?

Answer 14

The Memory Address Register holds the address of the memory location from which data or an instruction should be read from or written to.

Question 15

What are CPU Buses?

Answer 15

A CPU Bus is a set of parallel wires connecting computer components.

Question 16

What is the Memory Data Register?

Answer 16

The Memory Data Register holds the data read from memory or to be written to memory.

Question 17

What Architecture is used in Contemporary CPUs.

Answer 17

Modern processors use both the Harvard and Von Neumann Architecture.

The RAM holds both instructions and data, however the cache is divided into two separate memories for data and instructions.

Question 18

What is the Data Bus?

Answer 18

The Data Bus is a Bi-Directional Bus used to transfer data and instructions between system components.

Question 19

What are the lines of the Control Bus?

Answer 19

Bus Request - used by a device to request access to the data bus.
Bus Grant - used to grant a device access to the data bus.
Memory Write - Causes the data on the data bus to be written to the memory address stored in the address bus.
Memory Read - Causes the data at the address on the address bus to be copied to the data bus.
Clock - synchronizes system processes.

Question 20

How can a devices performance be improved?

Answer 20

Upgrade CPU
Add More RAM
Upgrade GPU
Upgrade to faster Secondary Storage
Upgrade OS
Check for Viruses

Question 21

What is the Central Processing Unit?

Answer 21

The CPU executes instructions stored in memory.

Question 22

What is the Stored Program Concept?

Answer 22

The Stored Program Concept is the idea of a machine that fetches and executes instructions serially using a processor that performs arithmetic and logical instructions.
(Also referred to as a Von Neumann Machine)

Question 23

What is the System Clock?

Answer 23

The system clock generates an oscillating signal which schedules the CPU, as every instruction starts on a new clock pulse.

Question 24

Compare the Von Neumann and Harvard Architectures.

Answer 24

The Von Neumann Architecture stores data and instructions in the same memory, meaning there is only one data bus and address bus. Programs written for this architecture can be optimised in size easily. PCs and Servers use this architecture.

The Harvard Architecture stores data and instructions in separate memories, meaning there are two sets of data and address instructions. Programs written for this architecture seem to be larger. Often used by embedded systems.

Question 25

What is the relationship between the data bus size and word size.

Answer 25

The data bus transfers data a word at a time, this means that a larger word size requires a larger data bus.

Question 26

How does the Number of Cores affect the Speed of a Computer?

Answer 26

Theoretically multiple cores should allow many multiple operations to take place simultaneously, greatly increasing processor speed.
However multi-core processors can be slowed down when an instruction in one core depends on the result of an instruction in another core and a lot of software isn’t designed to take advantage of these extra cores.

Question 27

What are the stages of the Fetch-Decode-Execute cycle?

Answer 27

Fetch:

• The address of the next instruction is copied from the PC to the MAR.
• The value stored in the MAR is copied to the address bus.
• Read signal sent on the control bus.
• Instruction at this address is copied to the MDR and the PC is incremented.
• Contents of the MDR is copied to the CIR.

Decode:

• The Control Unit decodes the instruction held in the CIR.
• The opcode is stored in the MDR and the operand is stored in the MAR.

Execute:
- The opcode is carried out on the operand.

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