Paper 1

sample rate

number of samples per second

bit depth

the number of bits available to store amplitude measures

IPv4

• dotted decimal as separators

• 4 numbers

• each ranging from 0-255

IPv6

• colons as separators

• 6 pairs of hexadecimal digits

• each ranging from 00 to FF

switch

• provides a dedicated connection for each connected computer

• has a switching table that contains a list of its physical ports and the MAC addresses of the devices connected to those ports

• allows efficient data transfer by reducing collisions

router

• connects different networks together

• typically found at the boundary of the LAN to the Internet

• has a list of its physical ports and the IP addresses of other routers connected to those ports

• uses these to make decisions as to which port to send out a packet to

• address resolution, converts private IP addresses into public IP addresses

LAN

• Local Area Network

• small geographical area

• network hardware used is usually owned by organisation

WAN

• Wide Area Network

• large geographical area

• network hardware used is usually rented

topology

the physical arrangement of devices in a LAN

POP

• Post Office Protocol

• an email protocol

• it covers the transfer of emails from the server to the client

• removes (pops) the emails from the server as it does so

IMAP

• Internet Message Access Protocol

• an email protocol

• used for transferring emails from a server to a client

• does not remove the email from the server

SMTP

• Simple Mail Transfer Protocol

• an email protocol

• used for sending emails from the client to the server

HTTP

• Hyper Text Transfer Protocol

• used for the transfer of HTML pages (web pages) from a web server to a client

HTTPS

• Hyper Text Transfer Protocol Secure

• covers the transfer of encrypted web pages from a web server to a client

FTP

• File Transfer Protocol

• covers the transfer of files from a server to a client and vice versa

IP

• Internet Protocol

• covers addressing

TCP

• Transmission Control Protocol

• controls the volume of traffic on the Internet (flow control), error detection and correction as well as encapsulation of data into packets

Client server

• a model

• one computer (server) is typically more powerful, it provides a service to client computers

Peer to peer

• a model

• all computers have equal status

model

a conceptual arrangement of the roles of the devices

star topology

• has a switch in the centre

• if the switch fails, the whole network fails

• easy to add new nodes

mesh topology

• every node is connected to each other

• has a high redundancy, no effect on network if a single device goes down

• difficult to add new nodes and expensive to cable

protocol layers

• grouping protocols with similarities in their function

• done to facilitate development at a particular layer, without having to be concerned about the impact on other layers

• promotes interoperability

standard

• technical specifications that specify how software and hardware components must work

• each standard will include one or more sets of protocols

protocol

a set of rules that determine how two devices will communicate

Ethernet

• a protocol that specifies how devices should be connected in a wired LAN

• defines how data should be transmitted using MAC addresses to determine which device the data should go to

• also defines what should happen if a collision occurs on the network

Wi-Fi

• a set of protocols that specify how devices can communicate wirelessly using radio waves

• defines the frequency band and channel that should be used for communication as well as transmission rates and how devices authenticate

Bluetooth

• a wireless protocol

• much shorter range than Wi-FI

• uses ultra-high frequency radio waves

• typically used to transfer files between mobile devices and for headphones

secondary storage

non-volatile storage devices that retains data when power is turned off

types of secondary storage

magnetic, solid state, optical

characteristics of magnetic

• usually the highest capacity

• usually the cheapest

• if kept stable then reliable

• heavy and bulky

• moving parts

characteristics of solid state

• more durable, no moving parts

• portable (USB stick)

• limited lifespan

• quickest read/write speed

characteristics of optical

• relatively cheap

• light and portable

• drive used to read the disc is considered unreliable

encryption software

• encrypts plain text into cipher text

• cipher text cannot be understood

• decryption requires encryption key

defragmentation

moving separated parts of a file together in memory (secondary storage)

compression

when the file size if reduced so it either takes less storage or is faster to transmit/download/upload

lossless compression

• no data is lost upon compression

• decompressed file is identical to the original file

lossy compression

• data has been lost after decompression

• decompressed file will be lacking some data that was originally present

• decompressed file is smaller than lossless decompressed file

utility software

• small programs that assist the OS in its running

• they are often bundled with the OS, although they can be downloaded separately

types of utility software

• encryption software

• defragmentation

• data compression

what operating systems provide

• user interface

• memory management and multitasking

• peripheral management and drivers

• user management

• file management

user interface

provides a means for the user to interact with the computer

memory management and multitasking

• manages the allocation of RAM and the use of virtual memory as the RAM gets full

• controls multitasking, when the computer rapidly alternates between multiple tasks

peripheral management and drivers

• peripheral is any device that sits outside of a computer like a keyboard

• driver is a specific piece of software designed to the let the OS interact with the specified peripheral

user management

• provides basic security

• requires a password to authenticate the user

• different users can be assigned different levels of access

• user profiles can be created and deleted

CPU

• Central Processing Unit

• carries out the execution of instructions required for programs to run

• also takes part in FDE cycles

FDE cycle

• Fetch Decode Execute Cycle

• instructions are fetched (from RAM)

• instructions are decoded

• instructions are executed

• the process is repeated

common CPU components

• ALU

• CU

• Cache

ALU

• Arithmetic Logic Unit

• carries out addition, subtraction, shifts and logical operations such as NOT, AND and OR

CU

• Control Unit

• carries out the decoding of instructions

Cache

• memory with very fast read-write speed

• temporarily holds recently/frequently used instructions

Von Neumann architecture (registers)

• PC

• ACC

• MAR

• MDR

PC

• Program Counter

• temporarily holds the address of the location of the next set of instructions/data to be fetched

• increments each FDE cycle

ACC

• Accumulator

• temporarily holds the results of calculations that have been carried out by the ALU

• also temporarily holds data that has been inputted or is about to be outputted

MAR

• Memory Address Register

• holds the memory location/address of the next instruction to be fetched

MDR

• Memory Data Register

• holds the data that has been fetched or is being sent to memory

embedded system

a computer system with a single function, inside a larger mechanical unit

examples of embedded systems

• microwave

• washing machine

• cars

properties of embedded systems

• highly efficient

• reliable

• cheap to produce

• compact in size

• low in power consumption

purpose + characteristics of embedded systems

• designed to carry out a limited number of tasks

• built within a larger device

• use a micro controller

• use firmware

units of data

• bit (0 or 1)

• nibble (4 bits)

• byte (8 bits)

• kilobyte (1000 bytes)

• megabyte (1000 KB)

• gigabyte (1000 MB)

• terabyte (1000 GB)

• petabyte (1000TB)

purpose of binary format

CPU is made up of many very small switches which are either on (1) or off (0), the states of these switches are represented with binary

sound file size

sample rate x duration (s)

image file size

colour depth x image height (px) x image width (px)

text file size

bits per character x number of characters

CPU characteristics that affect performance

• clock speed

• number of cores

• cache size

metadata

data about data

examples of metadata

resolution, colour depth, file size

left shift

• multiplication

• leftmost bit is discarded

• all bits move to the left

right shift

• division

• rightmost bit is discarded

• all bits move to the right

overflow

when the result of binary addition exceeds the available bits

loss of precision

when multiplying binary values and the overflow is lost

primary storage

• holds the data and instructions that the CPU needs to access while the computer is turned on

• includes RAM and ROM

RAM

• Random Access Memory

• holds the instructions that are currently in use

• is volatile, contents are lost when power is turned off

• has very fast read-write speed

• larger capacity than ROM

• can be edited

ROM

• Read Only Memory

• holds the first instructions a computer needs in order to start up

• contains BIOS (Basic Input Output System) and stores boot sequence

• fast read-write speed but slower than RAM

• is non-volatile, contents are not lost even when the power is turned off

• is read only, data can only be read and can’t be edited

virtual memory

• an extension of RAM located in secondary storage

• when RAM is close to being full, virtual memory is used so the computer remains operational

• data currently not in use is transferred here

• much slower read-write speed and negatively impacts system performance

factors that affect network performance

• number of users

• bandwidth

• latency

• error rate

• transmission media

number of users

too many users can slow down the network if there is not enough bandwidth for all the users

bandwidth

• the amount of data that can be sent and received at any given time

• measured in bits per second (bit rate)

latency

the delay between data being send and received

error rate

the measure of how many packets do not reach their destination

transmission media

• the type of cable used in wired connections

• wired connections offer a higher bandwidth than wireless connections

types of transmission media

• UTP

• coaxial

• fibre optic cable

WAP

• Wireless Access Point

• allows wireless devices to connect to a LAN

• it can share out its allocated frequency range amongst connected devices

NIC

• Network Interface Card

• can be wired or wireless

• provides the connection between the computer and a network

• stores the MAC Address

DNS

• Domain Name System

• a system for resolving a URL to an IP address

• needed because humans work with URLs whilst computers work with IP addresses

how DNS works

• a website is hosted on a computer called a web server

• a computer that accesses th website is the client

• the user enters a web address (URL) into the web browser

• the web browser send a request to a DNS server for the matching IP address

• if found, the IP address is returned to the user computer which then uses it to send a webpage request to the web server

hosting

typically storing data online (e.g. One Drive)

cloud services

other online servers that provide software as a service

cyber attack examples

• hacking

• malware

• data interception

• DoS and DDoS attacks

• brute force attacks

• SQL injection

• social engineering

• physical threats

hacking

gaining or seeking to gain unauthorised access to a computer, a network or its data

penetration testers

• preventative method for hacking

• legally ‘hack’ into a system and report suggestion on how the organisation can improve their cyber security

malware

• software designed to do harm to computer, a network or its data

• there are various types e.g. ransomware, viruses

anti-malware software

• preventative method for malware

• automatically scans any files downloaded to check they are not harmful and report if there is a risk

data interception

when data streams conveyed over a network are intercepted and usable data is captured

encryption

• preventative method for data interception

• prevents the hacker from being able to interpret intercepted data

DoS attack

• Denial of Service attack

• a deliberate attempt to stop users of a network accessing the services provided by overloading it with network traffic

DDoS attack

• Distributed Denial of Service attack

• computers from all over the world are innocently hijacked to take part in a DoS attack, each sending only a small part of the flood

• hijacking is usually done with malware

brute force attack

where the hacker makes repeated attempts to gain entry to a computer or a network, commonly by repeatedly trying to guess their password

strong password

• preventative method for brute force attacks

• one that is not easily guessed or discovered

• should contain: upper and lowercase letters, digits, special characters, and minimum 8 character in length