Computer science AS level

Allows user to interact with the system allowing user to install and do what they want

Provides an interface for program to interact with the hardware so applications can access hardware to run through OS

Hardware is limited as such memory must be allocated and managed as to not run out

memory protection making sure processes cant be overridden by a program

Used to access external devices through drives allowing communication between computer and peripheral which enables the sending and receiving of data as well as handling buffer and interrupts from I/O port

Storage space is divided into file allocation units space is allocated to a particular file, creates and maintains directory structures

OS controlling what can be accessed by whom i.e clearance

When there is an error it will halt the program and save as much data possible then restart

Delete storage and check if everything is readable and writable then reinstalls

Fragmented data has a slower access time as such it is moved together by the HDD defragmenter to reduce access time and make the data contiguous

creates backup files at regular intervals

data compression method where the logical size of a file is reduced to save and facilitate faster data transmission, usually computer comes with lossy compression as most information is represented in a format where data cannot be lost

protect the computer from viruses scans files to protect computer system

the practice of using a network of remote servers hosted on the Internet to store, manage, and process data, rather than a local server or a personal computer.

• Used to connect to a network wirelessly

• via the use of an antenna

• can decode packets

• can encode packets

regenerates signal

functions as a central connection point within a LAN which broadcasts messages to all devices within the network

Connects two LANs of the same protocol

to recieve transmission from devices and forward them to their destination, allowing 2 or more devices to communicate with eachother

connects 2 networks of different protocols

allow connection of devices using radio signals

• recieve packets from the internet or external networks

• forward packets to their destination

• assign private IP's in a LAN

• Store a routing table

• finds most efficient route to destination

• implements firewall

• the list of shapes involved in an image // a list that stores the command/description required to draw each object

Data about the shapes, defines one aspect about the obejct being drawn

Data about a bitmap image for example number of colours

The rate at which amplitude of the sound is recorded (at regular intervals)

• Less quantization errors (diff between real and recorded sound)

• Less gaps in the sound wave as such the sound is recorded more often
  Disadvantages:

• Increased File size

• Not all audio playback devices support higher sample rates

Number of bits used to represent sound amplitude (also known as bit depth) Advantages of increasing

• More amplitudes can be recorded

• quantisation errors are smaller Disadvantages

• increased file size

Local Area Network

• Covers a small geographical area

• Uses dedicated infrastructure // company owned infrastructure

Wide Area Network

• Covers a large geographical area

• Not owned by an organisation or company

All computers use unique security to keep their data, devices both consume and produce resources, clients and server are not differentiated

• Parts of a file can be downloaded separately

  Disadvantages

• There is reduced security

• There is no centralised server, disorganised

Networking system whereby client computers rely on servers to perform their processing tasks.

Networking system where the client computer completes the majority of the processing and minimal processing is done by there server

Twisted pair has the lowest cost but also lowest bandwidth the need for attenuation increases with higher frequency, and is worst affected by interference, it needs repeaters often
Coaxial has relatively cheap cost but low bandwidth and need for attenuation increases a lot with higher frequency can recieve some interference and needs repeaters more often than not
Fibre optic cable
has the highest cost but highest bandwidth and is least affected with higher frequencies, there is little interference and does not need a lot of repeaters

Carrier Sense Multiple Access/Collision Detection Procedure:

1. Check if there is voltage in transmission medium

2. if there is activity wait a random amount of time and check again

3. if no activity is detected start transmission

4. continuously check for a collision

5. if no collision is detected continue transmission

6. if a collision is detected stop transmission of the message and transmit a jamming signal to warn all end stations after a random amount of time try again

When a call is placed a private cable is connected between the dialler and the reciever via circuit switching this is open indefinitely

IPv4: 32 bit long address represented as 4 groups of 8 bits represented as their denary character IPv6: 128 bit long address represented as 8 16 bit segments represented as 8 sets of 4 hexadecimal characters seperated by a colon

• The computer broadcasts a request for an IP address

• Assigns IP from within its scope

• The IPS's assigned is as a lease

The first IP address of the device that a client computer will look for when attempting to gain access outside the local network.

Process of dividing a network into multiple logical subnetworks when representing the subnets IP address a portion of the Host Id must be sacrificed

Adjusting the size of a network to be more realistic by reducing the amount of network or host id bits this change is shown as a prefix at the end of the IP address defining the length of the network id

Computing services over the internet or private internal network, only available to select users and not the general public, dedicated system only accessible for the organisation

Computing services offered by 3rd party provider over the public internet, open to anyone with appropriate equipment

incoming data is received into a buffer media player takes data from buffer and plays it
Advantages
Can be accessed at the users convenience
not as susceptible to having weak connections
Disadvantages:
Can lack real time interaction

content is being delivered the same its being generated, data is given to provider servers which compress it then to the users
Advantages
Allows for real time communication

Unique hardcoded identifier

BENEFITS

• Increases the number of allowed hosts in a LAN

• Decreases volume of broadcast and network traffic

• It enhances routing efficiency

• Improves network security and organisation

• Reduces network strain and congestion

1. User opens their browser and types URL

2. Browser asks the DNS server for the IP address

3. The DNS server checks its database to locate the IP or requests another DNS if it cant find it, it checks other DNS servers

4. The IP address is sent back to the users browser

5. The browser now sets up communication with the website server and required pages are downloaded

6. The browser interprets the HTML code and displays website on users screen

Pros and Cons

applications and services that are accessed, managed, and stored online through remote servers, providing users with flexibility, scalability, and accessibility from any device with an internet connection.

assembly instructions which cause data to change place

transferrence of data between the computer program an external sources such as keyboards
ex, INPUT AND OUTPUT

manipulation of numbers

Doing something if a certain condition has been met or doing it regardless

compares two different values

The address location is the operand

Using the address inside the memory location

Accessing the data inside an address + the value in the index register

Accessing data of the value proceeding the #

Accessing the address inside a given register

checks the environment for change when it notices a change it performs some sort of output

checks the environment for change if it notices change then it may record it or report it

a device that causes a machine or another device to do an action as a result of detecting an input

A portion of the output is fed back into the input, feedback ensures that a system operates within set criteria by enabling system output to effect subsequent system input thus allowing conditions to be automatically adjusted

Built in functions available when programming in a particular language

Advantages
- Saves time as you dont need to code your own functions
- Saves time as you dont have to error check these functions as they have most likely already been tested
- can perform complex calculations that the programmer may be unable to do

A shared library can be used in multiple programs simultaneously, If the library is updated it is updated in every program which uses it.

Advantages:
memory requirements of program is reduced as DLL is only loaded once
A single DLL file can be made available to multiple programs saving memory

Making sure data is accurate and up to date

Protecting data from loss / corruption

Ensuring data can not be accessed by unauthorised users

Mistreatment
Internal mismanagement
Natural disasters
Unauthorised intrusion into system
malware

may steal of encrypt sensitive data, may alter computer functions

Weak passwords
Not recognising phishing or pharming attack
may introduce malware accidently (downloaded files, email attachement)

increased security complexity means vulnerabilities may be overlooked in OS
App packages allowing macros to spread
Buffer overflow

Mayor updates can create vulnerabilities as such it will need to be checked

checks if user is authorised in a multiuser system normally via username or password

Not leaving computer on when unattended or allowing someone to observe computer access

A form of data verification used for error detection by adding a digit based on the previous digits in the string on the end of a string of bits

A method to check for data corruption from flipped bits by checking if the number of 1s has become even or odd

the formal and legal right of ownership which stops others from reproducing work without authorisation

Requires users to pay for a license to recieve the program, you are not given the source code and it is illegal to redistribute software

Free software available for a trial period or with limited capabilties

You are given the software as well as the source code as to allow the user to change and distribute it

free software which can be altered in anyway you wish and redistributed aims to improve software rather than earn any monetary value

Stores the current instruction while it is being decoded and executed

Stores a value; only used for indexed addressing

Stores the address of a memory location or an I/O component which is about to have a value read from or written to

Stores data that has just been read from memory or is just about to be written to memory

Stores the address of where the next instruction is to be read from

Contains bits that are either set or cleared which can be referenced individually

its sole function is to transfer an address for a location from the program counter or I/O component, to be loaded into the MAR

function is to carry data which may be a instruction address or value it is bidirectional

Connected to the CU and is bidirectional transmits signal from CI, part of the bus architecture carries commands from processor and receives status signals from components connected to the computer system, transmits clock interrupt and read write signals

electrical impulses which dictate the amount of F-E cycles per second,

Amount of cores affects the number of instructions which can be executed in a given amount of time can allow the user to run multiple programs at once with minimal performance issues, does not inherently double speed as they must communicate

The amount of bytes the system considers as one unit as such higher word lengths can contain more information as such more information can be executed per cycle

An interrupt is handled with the following steps

• Interrupts are checked for at the start/end of each F-E cycle

• Contents of PC and other registers stored safe in stack

• Appropriate interrupt handler or interrupt service routine initiated by loading start address into PC

• When the ISR program has been executed there is a check to see if there are further interrupts

• Further interrupts are dealt with by repetition of the ISR program

• If there are no further interrupts the stored contents of registers are restored to the Cpu and the originally running program is resumed.

There is no way to validate data entry, sensitive data may be accessed without the correct clearance may result in a loss of referential integrity

there are no repeating groups the fields are atomic

All attributes depend on all parts of a compound key

All data is fully dependent on the primary key, there are no many to many relationships, no non key dependencies, there are no repeated attributes

Allows users to enter criteria searches for data which matches the entered criteria organises results to be displayed to the user