computer science

RAM

Random Access Memory

- temporarily stores data and programs currently in use

- more RAM = more apps open

- storage measured in gigabytes

CPU

Central Processing Unit

- calculations and operations

speed measured in gigahertz

- faster CPU = faster response from computer

HDD

Hard Disk Drive

- non volatile, stores data outside of computer

- bigger HDD = more data storage

- has moving parts

SDD

Solid State Drive

- non volatile storage

- no moving parts

- read/write quicker than HDD

- low power consumption

ASCII

American Standard Code for Information Interchange

- substitutes a number for each character

- stored in binary using 7 bits

- 128 characters

colour depth

(bit depth)

- number of bits assigned to each pixel

- higher = more colours = larger file size

resolution

number of pixels

sound (data representation)

- microphone converts sound to electrical signal

- analogue to digital converter (ADC) digitises the signal

- via sampling the analogue signal

sampling frequency

how often the analog signal is measured

- determines sound quality and file size

lossy compression

- discards data

- reduces file size

- data to discard is chosen by algorithm

lossless compression

- reduces file size by storing data more efficiently

- original file can be recreated or uncompressed afterwards

Computer Networks

local area network (LAN)

- house or small company

wide area network (WAN)

- over 1km size

- across city or continents

non connected computers are standalone

network media

- Ethernet cables

- fibre optic

- wireless access points

- undersea cables

benefits of networking computers

- files can be accesses on any computer on the network quickly

- no download required

- peripherals (eg, printers) can be shared

- internet connection and email can be shared

- user profiles/security has centralised management

- centralised backup

software can be installed across a network

disadvantages of networking computers

- management is complicated and expensive

- viruses can infiltrate one computer and spread across network quickly

topology

layout or map of the different parts of a network

node

a client (computer) on a network

router

hardware that routes packets across a wide area network

server

central controlling computer on network

protocol

set of rules for communicating across a network

packet

what large data items are split into for sending across a network

ISP

chunk of info that can be sent of a network

larger files are broken into packets

IP adress

and internet protocol address

unique for each device connected to a network

encryption

used to protect data in case it is hacked or illegally hacked

ciphertext

an encrypted message

key

a sequence of numbers used to encrypt/decrypt

encryption algorithm

method used for encrypting the plain text

penetration-testing

pen testing

- professional security experts try to hack their own system

firewall

a securirty device

- monitors incoming and outgoing traffic

-can block access

network policies

in school sand businesses

- policies to keep network safe

- rules to guide users

malware

malicious software

- any program or file that is harmful to a computer user

- includes computer viruses, worms, Trojan horses and spyware

phishing

- sending emails pretending to be from reputable companies

- to sneak personal information

eg, passwords and credit card numbers

DOS attack

Denial Of SErvice attack

- spamming a website with packets do deny real users access

- crashes server

SQL injection attack

- users enter a SQL statement into a form in which they are supposed to enter a name or other data

eg, username == true

cores

- where instructions are executed in CPU

- cpu can have multi-core

- 2 cores may result in double the speed (other factors may change this)

- effects cpu speed

quartz clock

- vibrations per second (Hz)

- 1M Hz executes 1M instructions per second

- clock speed effects CPU speed

cache in CPU

- expensive

- super fast

- small amount of memory on processor chip

- holds commonly used instructions