Unit 1 Components Of A Computer

Question 1

Processor

Answer 1

The processor is the brain of a computer. It executes instructions which allows programs to run.

Question 2

The Arithmetic and Logic Unit

Answer 2

The ALU (Arithmetic and Logic Unit) completes all of the ​arithmetical and logical operations​. Arithmetical operations include all mathematical operations such as addition and subtraction on fixed or floating point numbers. Logical operations include boolean logic operations such as AND, OR, NOT, and XOR.

Question 3

The Control Unit

Answer 3

The Control Unit is the component of the processor which ​directs the operations of the CPU​. It has the following jobs:

• Controlling and coordinating the activities of the CPU
• Managing the flow of data between the CPU and other devices
• Accepting the next instruction
• Decoding instructions
• Storing the resulting data back in memory

Question 4

Registers

Answer 4

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 5

Program Counter (PC)

Answer 5

Is a register that manages the memory address of the next instruction to be fetched and executed.

Question 6

Accumulator (ACC)

Answer 6

These hold the data being worked on and the results of arithmetic and logical operations.

Question 7

Memory Address Register (MAR)

Answer 7

This holds the RAM address you want to read to or write from.

Question 8

Memory Data Register (MDR)

Answer 8

This temporarily stores the data you have read from RAM or want to write to RAM.

Question 9

Current Instruction Register (CIR)

Answer 9

Holds the ​current instruction​ being executed, divided up into ​operand and opcode​.

Question 10

Buses

Answer 10

Buses are a set of ​parallel wires​ which connect ​two or more components​ inside the CPU. There are three buses in the CPU: ​data bus​, ​control bus​, and ​address bus​. These buses collectively are called the ​system bus​.

Question 11

Data Bus

Answer 11

This is a ​bi-directional bus​ (meaning bits can be carried in both directions) used for transporting ​data​ and ​instructions​ between components.

Question 12

Address Bus

Answer 12

This is the bus 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 13

Control Bus

Answer 13

This is a ​bi-directional​ bus used to transmit ​control signals​ between internal and external components.

Question 14

The control signals include:

Answer 14

• Bus request: shows that a device is requesting the use of the ​data bus
• Bus grant: shows that the CPU has ​granted access​ to the data bus
• Memory write: data is written into the addressed location using this bus
• Memory read: data is read from a specific location to be placed onto the data bus,
• Interrupt request: shows that a device is requesting access to the CPU
• Clock: used to ​synchronise operations

Question 15

Assembly language

Answer 15

Assembly code​ uses ​mnemonics​ to represent instructions, for example ADD represents addition. This is a simplified way of representing ​machine code​.

Question 16

Fetch phase:

Answer 16

• 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

Question 17

Decode phase:

Answer 17

The instruction held in the CIR is decoded. The instruction is split into oppose and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it. The operand holds either:
. The address of the data to be used with the operation, which is the copied to the MAR, or
. The actual data to be operated on, which will be copied to the MDR
. The data to be operated on may be passed to the ALU/accumulator

Question 18

Execute phase:

Answer 18

• The appropriate instruction/opcode is carried out on the operand

Question 19

Clock speed

Answer 19

The clock speed is determined by the ​system clock​. This is an electronic device which generates signals​, switching between 0 and 1. All processor activities begin on a clock pulse, and each CPU operation starts as the clock changes from 0 to 1. Clock speed is the number of cycles that are performed by the CPU per second.

Question 20

Number of cores

Answer 20

A core is an ​independent processor​ that is able to run its own fetch-execute cycle. The number of cores indicates the number of processing units in a computer. 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. However, not all programs are able to utilise multiple cores efficiently as they have not been designed to do so, so this is not always possible.

Question 21

Cache Memory

Answer 21

Cache is a small amount of expensive, very fast memory inside the CPU. 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 22

Von Neumann Architecture

Answer 22

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. Von Neumann architecture is built on the stored program concept.

Question 23

Harvard Architecture

Answer 23

Harvard architecture has physically separate memories for instructions and data, more commonly used with embedded processors.This is useful for when memories have different characteristics​, i.e. instructions may be read only, while data may be read-write.

Question 24

Advantages of Von Neumann Architecture

Answer 24

Cheaper to develop​ as the control unit is easier to design

Programs can be ​optimised in size

Question 25

Advantages of Harvard Architecture

Answer 25

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 26

Reduced Instruction Set Computers (RISC)

Answer 26

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

Question 27

Complex Instruction Set Computers (CISC)

Answer 27

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 28

RISC Processors

Answer 28

The compiler has to do more work to translate high level code into machine code.

More RAM is required to store the code.

Pipelining is possible since each instruction takes one clock cycle.

Question 29

CISC Processors

Answer 29

The compiler has less work to translate high level code into machine code.

Less RAM is required since code is shorter.

Many specialised instructions are made, even though only a few of them are used.

Question 30

Graphics Processing Unit (GPU)

Answer 30

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 31

Multi-core and Parallel Systems

Answer 31

Multi-core CPUs have ​multiple independent cores​ that can complete instructions separately which results in higher performance. Parallel systems accomplish a similar task however instead of requiring multiple cores they can complete tasks with a single core, by using ​threading​. Overall, in larger projects, multi-core systems perform better than parallel systems.

Question 32

Optical

Answer 32

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 33

CDs

Answer 33

CD stands for ​compact disc​. They use optical technology to store​ small quantities​ of information. Most commonly used for​ audio files​, CDs are small, thin and light which makes them very portable.

Their disadvantages include being​ easily damaged​ by scratches, their​ limited storage capacity ​and ​relatively slow transfer speeds​.

Question 34

DVDs

Answer 34

DVD stands for ​digital versatile disc​ or​ digital video disc​. Similar to CDs, DVDs are also optical devices which have a​ higher storage capacity than CDs​, making them suited to storing digital videos which require more storage space than audio files or photos.

Question 35

Blu-Ray

Answer 35

An advancement over DVDs, blu-ray discs have ​more than five times as much storage​ than traditional DVDs, making them useful for storing high-resolution films.

Question 36

Magnetic

Answer 36

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 37

Hard Disk Drives

Answer 37

HDD, hard disk drives typically have​ high capacities​ of between 500GB and 5TB. They 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 38

Magnetic Tape

Answer 38

Wound onto reels, long stretches of tape were passed through readers which would check the polarity of the tape and read off a binary value. Tape was a ​bulky ​way to store data and the technology was superseded by more modern technology.

Question 39

Flash

Answer 39

Flash storage is​ fast and compact​. 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 40

Flash memory

Answer 40

Flash memory can be erased and reprogrammed ​electronically​, and is ​non-volatile​, meaning it stores its data even when power is lost.

Question 41

Solid State Drives

Answer 41

Often referred to as SSDs, solid state drives are currently one of the most popular forms of data storage. They are extremely​ light and portable​, while having no moving parts - this makes them much more resistant to damage from movement than hard disk drives, which are packed with moving parts. Furthermore, SSDs are renowned for their high data transfer rates. The primary disadvantage of SSDs is their ​cost​, which continues to decrease as they become more common.

Question 42

RAM

Answer 42

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 more expensive per gigabyte​ than secondary storage devices, so computers often have only 4 or 8 GB or RAM compared to 100s or 1000s of GB of secondary storage.
RAM is volatile, meaning that it loses its information when power is lost.

Question 43

ROM

Answer 43

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.

Question 44

Virtual Storage

Answer 44

Virtual storage is the name given to storing information ​remotely ​so that it can be accessed by any computer with access to the same system, for example over the Internet. Examples of virtual storage include ​cloud storage services ​like Google Drive and Microsoft OneDrive as well as networked storage used in offices and schools.
As internet speeds increase, virtual storage is becoming a more popular method of storage thanks to the convenience of files being available “in the cloud” on any device connected to the Internet.
While virtual storage is ​convenient ​to access and share, its disadvantages include limitations of a user’s network speed and​ high costs

Question 45

Pipelining

Answer 45

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 46

Why is Pipelining used

Answer 46

Pipelining is aimed to reduce the amount of the CPU which is kept ​idle​. It is separated into instruction pipelining​ and ​arithmetic pipelining​. Instruction pipelining is separating out the instruction into fetching, decoding, and executing. Arithmetic pipelining is breaking down the arithmetic operations and overlapping them as they are performed.