Unit 1: Computer Components

Question 1

Describe the role of the Control Unit.

Answer 1

• Coordinates the activity of all other processor components
• Manages the phases of the Fetch-Execute cycle
• Decodes instructions received into the processor

Question 2

Name five registers used in the Fetch-Execute cycle.

Answer 2

• Program Counter (PC)
• Memory address register (MAR)
• Memory data register (MDR)
• Current instruction register (CIR)
• Accumulator (ACC)

Question 3

How is the Program Counter (PC) used in the Fetch-Execute cycle?

Answer 3

• Holds the address if the next instruction
• Incremented by one when the instruction is read, ready for the next cycle.

Question 4

How is the Memory address register (MAR) used in the Fetch-Execute cycle?

Answer 4

• Contains the address of the memory location from which data or an instruction is to be fetched.

Question 5

How is the Memory data register (MDR) used in the Fetch-Execute cycle?

Answer 5

• Temporarily stores the data being transferred to and from memory.
• It acts as a buffer, allowing the processor and memory units to act independently without being affected by minor differences in operation.

Question 6

How is the Current instruction register (CIR) used in the Fetch-Execute cycle?

Answer 6

Holds the instruction currently being decoded or executed.

Question 7

How is the Accumulator (ACC) used in the Fetch-Execute cycle?

Answer 7

Holds the result of an instruction.

Question 8

What is the purpose of the Arithmetic-Logic Unit (ALU) in the processor?

Answer 8

Used to carry out instructions received by the processor and produce the processed output.

Question 9

What is the System clock in the processor?

Answer 9

A continuously cycling signal that is used as a timing pulse for all processor components.

Question 10

What is a bus?

Answer 10

Buses are a set of ​parallel wires​ which connect ​two or more components​ inside the CPU.

Question 11

What does the system bus consist of?

Answer 11

The system bus consists of three separate buses carrying control signals, addresses and data

Question 12

What are registers?

Answer 12

Registers are ​small memory cells​ that operate at a ​very high speed​. They are used to temporarily store data​ and all ​arithmetic​, ​logical​ and ​shift​ operations occur in these registers.

Question 13

Describe the purpose of the Data Bus.

Answer 13

This is a ​bi-directional bus​ used for transporting ​data​ and ​instructions​ between components.

Question 14

Describe the purpose of the Address Bus.

Answer 14

Used to transmit the ​memory addresses​ specifying where data is to be sent to or retrieved from. The width of the address bus is proportional to the ​number of addressable memory locations​.

Question 15

Describe the purpose of the Control Bus.

Answer 15

This is a ​bi-directional​ bus used to transmit ​control signals​ between internal and external components. The control bus coordinates the use of the address and data buses and provides status information between system components.

Question 16

Name 7 control signals.

Answer 16

• Bus requests
• Bus grant
• Memory write
• Memory read
• Interrupt request
• Clock

Question 17

How is Assembly language processed by the CPU.

Answer 17

Assembly code​ uses ​mnemonics​ to represent instructions; the instruction is divided into ​operand​ and ​opcode​ in the Current Instruction Register. The operand contains the data or the ​address​ of the data upon which the operation is to be performed. The opcode specifies the ​type of instruction​ to be executed.

Question 18

What is Pipelining?

Answer 18

Pipelining is the process of completing the fetch, decode, and execute cycles of ​three separate instructions​ ​simultaneously​, holding appropriate data in a ​buffer​ in close proximity to the CPU until it’s required. While one instruction is being executed, another can be decoded and another fetched.

Question 19

What is the purpose of Pipelining?

Answer 19

Pipelining is aimed to reduce the amount of the CPU which is kept ​idle​. It is separated into instruction pipelining​ and ​arithmetic pipelining​.

Question 20

What is instruction pipelining?

Answer 20

Instruction pipelining is separating out the instruction into fetching, decoding, and executing.

Question 21

What is Arithmetic pipelining?

Answer 21

Arithmetic pipelining is breaking down the arithmetic operations and overlapping them as they are performed.

Question 22

Describe the sequence of operations in the Fetch-Decode-Execute Cycle.

Answer 22

Fetch phase:
- Address from the PC is copied to the MAR
- Instruction held at that address is copied to MDR by the data bus
- Simultaneously, the contents of the PC are increased by 1
- The value held in the MDR is copied to the CIR

Decode phase:
- The contents of CIR are split into operand and opcode

Execute phase:
- The decoded instruction is executed

Question 23

What three factors affect CPU performance?

Answer 23

Clock speed, number of cores and the amount and type of cache memory.

Question 24

How does Clock speed affect CPU performance?

Answer 24

All processor activities begin on a clock pulse, and the clock speed is the time taken for one clock cycle to complete. Consequently, the higher a system’s clock speed, the more instructions it can process over a given time.

Question 25

How does the Number of cores in a CPU affect it’s performance?

Answer 25

A core is an ​independent processor​ that is able to run its own fetch-execute cycle. A computer with multiple cores can complete ​more than one​ fetch-execute cycle at any given time. A computer with dual cores can theoretically complete tasks ​twice as fast​ as a computer with a single core in programs which are able to utilise multiple cores efficiently.

Question 26

How does the Amount and type of Cache Memory affect a CPU’s performance?

Answer 26

Cache memory is the ​CPU’s​ ​onboard memory​. Instructions fetched from main memory are copied to the cache, so if required again, they can be accessed quicker. As cache fills up, unused instructions are replaced.

Question 27

What are the three types of Computer Architecture?

Answer 27

• Von Neumann Architecture
• Harvard Architecture
• Contemporary Processing

Question 28

Describe Von Neumann Architecture.

Answer 28

This architecture includes the basic components of the computer and processor (single control unit​, ​ALU​, ​registers​ and ​memory units​) in which a ​shared memory ​and ​shared data bus​ is used for both data and instructions.

Question 29

Describe Harvard Architecture.

Answer 29

Harvard architecture has physically separate memories for instructions and data, more commonly used with embedded processors.

Question 30

Name two advantages of Von Neumann Architecture.

Answer 30

• Cheaper to develop​ as the control unit is easier to design.
• Programs can be ​optimised in size.

Question 31

Name two advantages of Harvard Architecture

Answer 31

• Quicker execution​ as data and instructions can be fetched in parallel.
• Memories can be different sizes​, which can make more efficient use of space

Question 32

Describe the difference in the devices used between Von Neumann and Harvard architecture.

Answer 32

Von Neumann architecture is used in PCs, laptops, and servers whereas Harvard architecture is used in digital signal processing, microcontrollers, and in embedded systems.

Question 33

Describe the processors in Reduced Instruction Set Computers (RISC).

Answer 33

In these processors, there is a ​small instruction set​. Each instruction is approximately ​one line of machine code​ and takes one clock cycle.

Question 34

Describe the processors in Complex Instruction Set Computers (CISC).

Answer 34

In these processors there is a ​large instruction set​. The aim is to try and accomplish tasks in as few lines of assembly code as possible. These instructions are built into the hardware​.

Question 35

What are the three main advantages of Complex Instruction Set Computers (CISC)?

Answer 35

• Quicker to code programs
• The compiler has less work to translate high level code into machine code
• Less RAM is required since code is shorter

Question 36

What are the three main advantages of Reduced Instruction Set Computers (RISC)

Answer 36

• The hardware is simpler to build
• Pipelining is possible because each instruction takes the same amount of time
• Better performance processors come at less cost due to RISC use of RAM and software

Question 37

Describe a Graphics Processing Unit (GPU).

Answer 37

A graphics processing unit (GPU) is a ​co-processor​ which has lots of​ independent processors​ working in parallel making it very efficient at tasks such as image processing, and machine learning.

Question 38

Describe how Multi-core CPUs can have higher performance.

Answer 38

Multi-core CPUs have ​multiple independent cores​ that can complete instructions separately which results in higher performance.

Question 39

Describe how Parallel systems can have higher performance.

Answer 39

Parallel systems accomplish a similar task however instead of requiring multiple cores they can complete tasks with a single core, by using ​threading​.

Question 40

Name the three main storage device types.

Answer 40

• Optical
• Magnetic
• Flash

Question 41

Describe how optical storage devices function.

Answer 41

Optical devices are read from and written to using ​lasers​. Information is represented by portions of the disc which either ​reflect ​or ​scatter the incident laser light written in spiral tracks on the disc’s surface.

Question 42

Describe an example of an optical storage device.

Answer 42

CDs - Small, thin, portable disc used to store small quantities of information, usually audio files. However, they are easily damaged, have limited storage capacity and slow transfer speeds.

Derivatives include DVDs and Blu-Ray.

Question 43

Describe how magnetic storage devices function.

Answer 43

Devices which store information magnetically represent binary information using ​two magnetic states​ which represent ​1​and ​0​, allowing any information to be represented in binary form.

Question 44

Describe an example of a magnetic storage device.

Answer 44

Hard Disk Drives (HDDs) - Hard disk drives typically have​ high capacities​ and work by rotating magnetic platters at high speeds under a read/write head on an actuating arm which allows the read/write head to access any part of the platter.

Disadvantages of HDDs include their somewhat ​slow data transfer speeds​ and their tendency to become damaged by movement. The combination of brittle platters and moving parts results in a delicate device.

Question 45

Describe how flash storage devices function.

Answer 45

The technology makes use of silicon ​semiconductors ​forming the logic gates NAND and NOR to store electrical charge in one of two states: high or low. These two states represent the binary values True and False, which can be used to represent information.

Question 46

Describe an example of a flash storage device.

Answer 46

Solid State Drives (SSDs) - Extremely​ light and portable​, while having no moving parts meaning they are much more resistant to damage from movement than HDDs. SSDs have very high data transfer rates, with primary disadvantage being cost.

Question 47

What is RAM?

Answer 47

Random access memory is a type of ​fast ​main memory used to store data and programs that the computer is currently using.
This speeds up the computer’s execution as RAM has higher access speeds than even flash memory.
RAM is significantly more expensive per gigabyte​ than secondary storage devices, and it is volatile; it loses its information when power is lost.

Question 48

What is ROM?

Answer 48

Read only memory, as the name suggests, ​cannot be modified​. Once programmed, the state of the memory cells inside does not changed. ROM is non-volatile, so it retains its data even when the computer is powered off.