IGCSE CIE COMPUTER SCIENCE TERMS

ISP (internet service provider)

company charging monthly fee that provides internet access

IP (internet protocol) address

assigned by ISP, unique to each internet session

MAC address

number which uniquely identifies a device - 1st half = manufacturer, 2nd = device itself - made up of 6 groups of hex digits

HTML Structure

essential parts of document including semantics and structural markup

HTML Presentation

how the document looks/sounds

CSS - Cascading Style Sheet

contains everything that controls webpage presentation

HTTP - hypertext transfer protocol

a set of rules which must be followed when transferring files across the internet

HTTPS

a SECURE set of rules which must be followed when transferring files across the internet

web browser

software that allows a user to display a webpage on their screen - they interpret html code and show the result

URL - uniform resource locator

used to find/identify a webpage on the internet

cookies

packet of information sent from web server to web browser - creates anonymous user profile, and used in advertising

actuator

The actuator is a mechanical device or motor which carries out the action or decision made by the control system.

loudspeaker

output device that produces sound using voltages at different levels which vibrate a cone in speaker housing

LED

Used for backlighting a monitor/tv - they are thin, produce a white light, and do not require much power

CCFL

Old technology used for backlighting - took time to warm up, and produced yellow-ish lighting + required a lot of power

LCD

used in projectors - high intensity light beam was passed through display, then onto screen

OLED

new technology used for tv/monitor screens, using a cathode and anode. Flexible, no backlighting required.

DLP

light projector using mirrors to produce 1024 different grey shades. A bright white light source passed through colour filter allowing 16million colours to be created.

RAM

a type of memory that is read-write and volatile. Used for main memory

ROM

memory that is hard coded at time of manufacture. Stores start-up programs and BOOTSTRAP

volatile

memory that loses its contents when the power is off eg. main memory

non-volatile

memory that doesn't lose its contents when the power is off e.g. hard disk

secondary memory/storage

long-term, non volatile storage media e.g. hard disk

off-line storage

storage that can be physically moved away from a device and stored somewhere else e.g. CD, USB stick, DVD

virtual memory

part of the hard disk that is programmed to work as an extension of main memory

optical media

secondary storage that is read using lasers e.g. CD, DVD

solid state/flash memory

secondary storage with no moving parts; used in memory sticks, cameras and phones

FAT - file allocation table

a map of where each file is and which sectors on the magnetic disk are free

address bus

unidirectional, carries address related signals from the memory to processor

control bus

unidirectional, carries control related signals throughout the computer

data bus

bi-directional, carries data between memory and processor, and between input/output and processor

operating system

software running in the background of a computer system managing basic functions, and making the computer user-friendly

interrupt

signal sent from device/software to processor, causing it to stop what it is doing. Allows multi-tasking

buffers

temporary memory areas in a computer that allow the hard drive to continue to function while something loads from memory

program

our way of telling a computer what to do, how to do it, and when to do it

high level language

portable language designed with the programmer in mind - it is easy to understand and debug, but it needs to be translated in order for a computer to understand it

low level language

language relating to specific architecture and hardware of a particular device - can refer to assembly lang or machine code

assembly language

code that is specific to a particular hardware, but needs to be translated into machine code before it can run

machine code

the binary code that is specific to a machine and does not need translating in order to run

translator

program that changes higher level language into machine code

compiler

this translates HLL into machine code. Once it has done this, the program can be used multiple times without translating it again

interpreter

this translates HLL into machine code one line at a time.

assembler

this translates assembly language into machine code. Once it has done this, the machine code can be used multiple time without translating it again.

UPS

uninterruptable power supply

hacking

gaining illegal access to a computer/computer system

cracking

editing source code with malicious intent

viruses

program or code that can replicate itself with intention of deleting files, corruption or malfunction. Not always malicious

phishing

using legitimate - looking emails to trick users and gain personal information from them

pharming

a piece of software leading a user to a bogus website - used to gain personal information

wardriving

stealing someone's WiFi

spyware/key logging software

hardware or software that can be used to monitor key presses and gain information.

firewall

this examines traffic between a user's computer and the internet by checking what is/isn't allowed and blocking traffic that does not meet certain criteria

proxy server

this filters web traffic, keeps the IP address secret, and, using a cache, speeds up access to websites that have been visited before

SSL

this is used on web browsers to allow data to be sent/received securely. It encrypts data so that only the sender and receiver can understand the information being transmitted

TLS - Transport Layer Security

this is a form of secure data transmission made up of 2 layers: the record protocol, and the handshaking protocol. It is very secure and fairly new, and can make use of session caching, which improves performance. It involves many complicated encryption algorithms.

session caching

this is used in TLS to avoid using too much computer time; TLS is able to attempt to resume an existing session, which increases speed.

symmetric encryption

this uses a secret key that could be a combination of characters. The same key is needed by both sender and receiver to encrypt and decrypt the message

asymmetric encryption

this is a type of encryption using both a public and a private key. The public key can be seen by anyone, and used to encrypt messages to the receiver. The private key is used by the receiver to decrypt the message sent to them.

plain text

text/data before it has gone through encryption algorithm

cypher text

output from encryption algorithm

authentication

used to verify that data comes from a reliable source; used with encryption to strengthen internet security

denial of service attack

attempting to prevent a user from accessing part of a network (usually the server); this is usually temporary, but may be very damaging, or a big security breach

computer ethics

this considers 3 factors; intellectual property rights, privacy issues, and a computer's effect on society. It is a set of principles that regulates the use of a computer

code of ethics

this is a set of rules set up by the ACM and IEEE to ensure that computers are used correctly, and to avoid plagiarism.

free software

software that is free to run, copy, change or adapt, and share with friends, family or colleagues.

freeware

software that a user can download for free from the internet, but they are not allowed to edit the source code

shareware

software that users are allowed to try out, free of charge, for a certain period of time. It often lacks certain features that can be downloaded in the full, paid version.

4 uses of hexidecimals

- debugging

- MAC addresses

- HTML colours

- assembly language and machine code

Parity Checking

used to check whether data has been changed or corrupted following transmission from one device to another

Automatic Repeat Request (ARQ)

method to check if data has been transmitted correctly

Checksum

Data is sent in blocks and an additional value sent at the end of the block

Echo check

When data is sent to another device, this data is sent back again to the sender, then the sender compares the two sets to check if any errors occurred

Lossless data compression

All the data bits from the original file are reconstructed when the file again is uncompressed

Lossy data compression

The file compression algorithm eliminates unnecessary bits of data like MP3 and JPEG formats

Serial data transmission

one bit at a time over a single wire

- longer distance

-slower

Parallel data transmission

1 byte of data is sent down several wires at the same time

- short distance

- faster

Simplex data transmission

one direction only

Half-duplex data transmission

both directions but not at the same time

Full-duplex data transmission

in both directions simultaneously

Stored program concept

program instructions and data are stored in main memory and instructions are fetched and executed one after another

capacitive touchscreens

Electrical current is sent from the four corners of the screen. When your finger (or stylus) touches the screen, the current changes. This allows the location of the touch to be calculated

capacitive touchscreens a/d

adv- very durable surface

- allows for multi-touch

disadv- cannot be used wearing standard gloves

- glass screen can easily break/shatter

resistive touchscreens

These use multiple layers of material that transmit electrical currents. When the top layer of the screen is pushed/touched into the bottom layer the electrical current changes. This allows the location of the touch to be found.

resistive touchscreens a/d

adv- inexpensive to manufacture

- Can use stylus, finger, gloved finger or pen to

operate

disadv- Vulnerable to scratching

- Wears through time

- Does not allow multi-touch

infra-red touchscreens

These use a pattern of LED infra-red beams to form an 'invisible' grid on the screen. Sensors detect where the screen has been touched by detecting a break in the infra-red beams. The position of touch is then calculated.

infra-red touchscreens a/d

adv- good durability

- Allows multi-touch

- Can use stylus, finger, gloved finger or pen to

operate

disadv- expensive to manufacture

- sensitive to dust and dirt

- breaks easily

Why do computers use binary?

To store data

What is a byte?

The byte is a unit of digital information that most commonly consists of eight bits.

advantages/dis of parallel

ad-fast

disadvantages-expensive,short distances

usb transmission method

asynchronised