Section One - Components of a Computer System

will be updating weekly with more questions https://knowt.com/folder/49ce6500-b988-4e7b-80d1-418b6bfacb79

What is a computer?

A computer is a machine that processes data

What is the purpose of a computer?

To take data, process it and produce an output

What is hardware? 2 examples

The physical things that make up a computer. Examples: Monitor and CPU

What is software? 2 examples

The programs and applications that a computer system runs. Examples: Operating System and Word Processor

What is an embedded system?

Computers that are built into other devices that are often used to control and monitor machinery

Pros of embedded systems

Easier to design, cheaper to produce and more efficient as they’re dedicated to a single task

Cons of embedded systems

Less functionality, less variability in the things it can do

What does CPU stand for?

Central Processing Unit

What does the CPU do?

It processes all of the data and instructions in order to make the computer functional

What affects the CPUs processing power?

Clock speed, number of cores, cache size

What is the main computer architecture?

Von Neumann

What are the three main parts of the CPU?

Control Unit, Arithmetic Logic Unit, Cache

What does the Control Unit do?

It controls the flow of data inside the CPU (to registers, etc) and outside the CPU (to main memory, etc) and manages the fetch-execute cycle

What does the ALU do?

All the calculations, logic operations and binary shifts

Which register does the ALU house?

The accumulator

What is cache?

On board memory for the CPU, faster than the RAM but slower than registers

Why is cache useful?

It stores regularly used data to allow faster access times when the data needs to be retrieved

What are the downsides to cache memory?

They are low capacity and expensive compared to slower memory forms (RAM, secondary storage)

What are the levels to cache and their characteristics?

L1, L2 and L3, L1 has the lowest capacity but fastest access times whereas L3 has the highest capacity but slowest access times

What are registers and what do they do?

They temporarily hold data needed by the CPU, they are extremely fast and small pieces of onboard memory, crucial in the fetch-execute cycle

Example of registers

Program Counter, Accumulator, Memory Address Register, Memory Data Register

Program Counter - where is it and what does it do?

In the Control Unit, it holds the address in memory of the instruction for each cycle

Accumulator - where is it and what does it do?

In the ALU, it stores the results of calculations performed in the fetch-execute cycle

Memory Address Register - what does it do?

It holds any memory address (for data or an instruction) about to be read by the CPU

Memory Data Register - what does it do?

It holds the data or instruction after being read from or about to be written to memory

How does the CPU carry out the fetch-execute cycle? (common 6 mark question)

FETCH

• Read and copy memory address from the Program Counter to the MAR

• Read and copy the instruction stored at the address in the MAR to the MDR

• Increment the Program Counter to point to the memory address of the next instruction

  DECODE

• The instruction in the MDR is decoded by the Control Unit

• The Control Unit may then prepare for the next stage by loading certain values into the MAR/MDR

  EXECUTE

• The instruction is performed, which could be loading data from the memory, writing data to the memory, perform a calculation or logic operation, change the address in the PC or halt the program altogether

What is volatile memory? (1 Example)

It is temporary memory, it needs power to retain the data inside. Example: RAM

What is non-volatile memory? (1 Example)

It is permanent memory, keeps its contents even without power. Example: ROM

RAM - what is it and what is it used for?

Random Access Memory, it is high speed volatile memory often used as the main memory in a computer system. It can be read and written to and is where all data, files and programs are stored while in use.

What is virtual memory and when is it used?

A place in secondary storage where data can be moved if the RAM fills to capacity, it is used when too many programs/data/files are open at once or one particularly memory intensive program is being run

How does virtual memory work?

The computer moves data that hasn’t been recently used from the RAM into a place in secondary storage. When the CPU needs to read the data stored in the virtual memory, it has to move it back to RAM

Disadvantage of virtual memory and why

Can make a computer slow to respond when switching between applications or running a memory intensive program, this is because the access time for secondary storage vs RAM is significantly slower which in turn increases the process time for each instruction

What happens when a computer boots up?

• The CPU reads the BIOS instructions from ROM which tells the CPU to perform self-checks such as test memory, hardware checks, etc

• The OS is copied from secondary storage to RAM allowing the user interface to load and the computer to start running

ROM - what is it and what is it used for?

Read Only Memory, it is a small factory-made chip built into the motherboard of the computer that contains the instructions the computer needs to boot up (BIOS). As it is read-only, the chip cannot be written to but it is possible to update (flash) the BIOS

what are the 3 factors that affect CPU performance?

clock speed, number of cores and cache size

Clock speed - what is it and how does it affect the CPU performance?

The number of instructions a single processor core can carry out per second. Higher clock speed means instructions are carried out faster

What is overclocking a CPU and how can it be dangerous?

When a CPU is made to run at a higher clock speed than the factory set rate, if not done properly the CPU can overheat causing permanent damages to the system, to prevent this high performance cooling systems are usually needed

Number of cores - what is a core and how does this affect CPU performance?

They are each individual processing unit in a CPU that can process instructions independently. The more cores in a CPU the more instructions that can be carried out at once. Most PCs and smartphones have 4 or more cores.

why doesn’t increasing the number of cores automatically increase the performance?

software needs to be designed to use multicore processing meaning some data and instructions won’t benefit from more cores. also, instructions that are dependent on one another will stall a core, waiting for the other data to be processed which reduces efficiency

Cache Size - how does it affect CPU performance?

A larger CPU cache gives the CPU faster access to more data needed to process instructions

RAM - how does increasing it affect the overall performance of the computer?

The more RAM available, the more programs or more memory intensive programs can be run smoothly, leading to better performance. However, if a computer already has enough RAM to run everything the user wants, increasing RAM will make no difference to the performance

GPUs - what are they and what are they used for?

Graphics Processing Unit, they are specialised circuits for handling graphics and image processing in a CPU, which frees the CPU to process other data. Dedicated GPUs (graphics cards) can be used to increase the graphics quality for purposes such as PC gaming and design software

what is primary storage?

The memory areas that the CPU can access very quickly, they are often volatile eg. register, cache, RAM

what is secondary storage?

non-volatile storage where all data is stored when not in use eg. SSDs, HDDs, CDs

Hard Disk Drives - what are they?

A stack of magnetised metal disks that spin thousands of times a second, data is stored magnetically in small areas on the disks’ circular tracks, a movable arm can access these areas to read or write data

Advantages of HDDs (versus SSDs)

• Cheaper

• High Capacity

• Long lasting + reliable

Disadvantages of HDDs

• Easily damaged by impact

• Slower access times

• Need defragmenting

• Susceptible to strong magnets corrupting data

• Noisy

Solid State Drives - what are they?

A storage device that uses flash memory (non-volatile RAM) to store data, other common types of flash memory are USB sticks and SD cards

Advantages of SSDs (versus HDDs)

• Faster read/write times

• Don’t need defragmenting

• More durable

• Not susceptible to magnets

• Silent

Disadvantages of SSDs

• Expensive

• Shorter life

Optical Discs - what do they include and how do they work?

Include CDs, DVDs and Blu-Ray discs, each with increasing capacity. Optical devices (that read/write data to the discs) use a laser to scan the surface of the discs where there are tracks, each with areas of lands and pits indicating binary values 1 and 0 based on the reflection of light from the laser to the sensor, lands reflect the light back (1) where pits scatter the light (0)

what are the different forms of optical discs and what are they used for?

ROM media has data pre-written onto it, and cannot be overwritten. Used for games, music and film

R media has data written on it only once and cannot be written to again. Used for copies of data

RW media can be written to over and over. Used for anything

Advantages of Optical Discs

• Very cheap per GB

• Portable

• Can’t be damaged by water or shocks

DIsadvantages of Optical Discs

• Relatively low capacity

• Slowest read/write speed

• Can be easily scratched

Magnetic Tapes - what are they and what are they used for?

Reels of tape that can be magnetised to store data, used by large organisations for archives of large amounts of data

Advantages of Magnetic Tape

• Massive storage capacity

• Extremely low cost per GB

• Fast read/write speeds

Disadvantages of Magnetic Tape

• Needs specialist equipment to read/write data

• Slow searching for specific data

Order of secondary storage for read/write speed (fastest to slowest)

1. SSD

2. HDD

3. Magnetic Tape

4. Memory Cards

5. Optical Discs

Order of secondary storage for average cost per GB (lowest to highest)

1. Magnetic Tape

2. Optical Discs

3. HDD

4. Memory Card

5. SSD

Order of secondary storage for average capacity per unit (highest to lowest)

1. Magnetic Tape

2. HDD

3. SSD

4. Memory Card

5. Optical Discs

OS - what is it and what does it do?

A complex piece of software found on most computer systems. They exist to:

• communicate with internal and external hardware (via device drivers)

• provide a user interface

• provide a platform for applications to run on

• allow the computer to multitask (through memory management and controlling the CPU)

• deal with file and disk management and organisation

• manage system security and user accounts on the device

Device Drivers - what are they and what do they do?

Pieces of software that act as translators for the signals between the OS and the hardware. The OS chooses the right device drivers in accordance with the hardware detected, if a new piece of hardware is detected, the relative device driver is installed

UI - what is it and what does it do?

User Interface, allows the user to interact with a computer system

what are the two types of UI

GUI - Graphical User Interface

CLI - Command Line Interface

GUIs - what are they?

They are user interfaces that rely on visual stimulus to prompt the user's input, they have been WIMP-based in the past, but Android and iOS have adapted that for touchscreens

WIMP

Windows, Icons, Menus, Pointers

A guide to key elements of GUIs

Advantages of GUIs

• Easy to understand for everyday users

• Intuitive

• Interactive

• Less prone to errors

CLIs - what are they?

A text based interface where the user enters specific commands to complete tasks

Advantages of CLIs

• More efficient for advanced users

• Less resource heavy

• Can be used to automate processes

How does the OS allow for multitasking?

By managing memory and CPU processing time:

• when an application is opened the OS will decide when and which parts need to be moved to memory and will continue throughout the programs runtime

• when multiple applications are opened, the OS allocates certain memory addresses to certain applications to ensure data is not overwritten

• it also organises instructions into the most efficient order to be processed (by the CPU) in

what is file management?

the organisation of data into a usable hierarchical structure, deals with the naming, saving, movement, editing and deletion of data

how does the OS manage the hard disk?

it splits the disk into storage sectors, writes data to the disk in given sectors and keeps track of free space on the disk. it also organises and maintains the hard disk with utility software

what is a single user OS?

an operating system that only allows one user to use the computer at once eg. Windows

what is a multi user OS?

an operating system that allows several users to use the computer at the same time, these are often on mainframes and give simultaneous access eg. ATMs allow many people access to the bank's mainframe at the same time

how does the OS ensure data is kept private for each user on a system?

it allows each user to have access to only specific data that has been approved and their own personal data

often anti-theft measures are in place to prevent other users from accessing data they shouldn’t do such as password protected user accounts

Defragmentation - what is it?

putting broken up files stored in memory back together

why does defragmentation need to happen?

as files are moved, deleted and change size, gaps appear in the memory

these gaps are then filled by new data being written to the disk but that can further fragment the overall data on the hard disk causing the time needed to read/write data to the disk to increase

what does defragmentation software do?

reorganises data on the hard drive to put fragmented files back together, it also puts the free space together to reduce further fragmentation

why does defragmentation only need to happen on hard disks (rather than SSDs)?

SSDs have no moving parts and use flash memory so data can be found quickly wherever it is stored, defragmentation can sometimes shorten the lifespan of SSDs

Compression Software - what is it and what does it do?

a piece of software that reduces the size of files by permanently or temporarily removing data from them, these compressed files are quicker to download and take up less disk space

Encryption Software - what is it and what does it do?

a piece of software that encrypts and decrypts data to stop unwanted third parties from accessing it

to decrypt the data, the computer uses a unique key and a set of instructions to unscramble the data so it can be understood