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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
Note 
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