GCSE Computer Science - paper 1

Central Processing Unit (CPU)

processes data and instructions by following the:

FETCH- DECODE- EXECUTE cycle

Control Unit (CU)

¬ executes program instructions by following FDE cycle

- controls data flow inside CPU to registers and outside CPU

- Overall control of CPU

Program Counter (PC)

holds memory address of the instruction for each cycle

cache

¬ very fast memory but slower than registers.

- Stores regularly used data to access quickly.

- low capacity but expensive

- different levels (l1 quickest but lowest capacity)

von neuman architecture

data and instructions stored together in memory

Memory Address Register (MAR)

holds the memory address about to be used by the CPU, which can point to specific data or CPU instructions

Memory Data Register (MDR)

holds the data or instructions fetched from memory or waiting to be written to memory

Arithmetic Logic Unit (ALU)

¬ carries out calculations and logical operations.

- contains accumulator which is used to store intermediate results and calculations

clock speed

¬ the speed which instructions are executed in cycles per second.

- measured in hertz

- 500MHz = 500 mill instructions

- 3GHz = 3 bill instructions

embeded systems

computers built into a larger system that perform specific tasks with one circuit board

accumulator

intermediate results of logic and arethmetic results are stored

core

¬ process data independantly

- more cores = instructions processed faster

Random Access Memory (RAM)

¬ main memory

- volatile (loses data when off)

- more RAM = better performance

- stores: applications, GUI, OS

Read Only Memory (ROM)

¬ CPU reads instructions from ROM

- non-volatile (keeps data when off)

- smaller capacity

- stores: BIOS

Dynamic Random Access Memory (DRAM)

used as main memory

Static Random Access Memory (SRAM)

¬ used for cache memory

- small capacity

- fast access

virtual memory

¬ memory temporarily created on storage drive

- used when RAM is full

Fetch-Decode-Execute cycle (fetch)

1# copy memory address from PC to MAR

2# copy instructions stored in MAR to MDR

3# increment PC to point to address for next instruction

Fetch-Decode-Execute cycle (decode)

4# instruction in MDR decoded by CPU

Fetch-Decode-Execute cycle (execute)

5#instruction performed

# load data, calculations, logic operations, hault program

flash memory

¬ programmed electronically

- non- volatile

- used in: SD cards, USB sticks...

- fast

- portable

- no moving parts

- more expensive

- capacity smaller than HDD

primary storage

¬ memory areas where CPU can access quickly

- fastest read / write speeds

- mostly volatile

- registers

- cache

- ROM

- RAM

secondary storage

¬ where data is stored when not in use

- non- volatile

- (HDD, SSD)

- read / write speeds much slower than primary storage

tertiary storage

¬ used for archives and back ups for large amounts of data

- non- volatile

- stores data long term

magnetic storage

- demagnetised (0)

- magnetised (1)

- moving parts to read / write disk

- LARGE capacity (3TB)

- low cost

- fast read / write time

- not very portable

- can be damaged (heat, magnetic field)

- generally reliable

Solid State Drive (SSD)

¬ used for internal storage

- no moving parts

- use flash memory

- back up and transport data

- much faster read/ write times than HDD

- up to 500GB

Hard Disk Drive (HDD)

¬ traditional internal storage for laptops / PCs

- made from stack of magnetised metal disks

- data stored magnetically in sectors within circular tracks

- heads on arms access sectors on disk

- portable HDDs back up and transport large data amounts

- long lasting (reliable)

- can be damaged by dropping

HDD advantages

# cheaper

# higher capacity

# longer read / write life

SSD advantages

# faster

# don't need defragmentation

# more shock- proof

# don't make any noise

optical discs

¬ data is held on a reflective disk

- laser beam shined on disk

- reflect (0)

- doesn't reflect (1)

- CD = 700MB

- DVD = 4.7GB

- Blu-Ray = 25GB

- CD-ROM = read- only

- CD-R = write- once

- CD-RW = rewritable

- cheap per GB

- portable

- robust (can easily be scratched though)

- slow transfer speed compare to SSD

Operating System (OS)

¬ runs and maintains a computer system

- provides a UI (GUI)

- command line interface is text based, specific commands and knowledge needed to understand

- can run multiple tasks

- handles files and disk management (defrag)

- allow single-user or multi-user (i.e windows 10 = 1, bank ATMs = multiple)

defragmentation

¬ reorganises data on HD by putting fragmented files together

- if files are all together, read / write times much quicker and easier to find

full back up

¬ copy of every file on system

- use lots of storage space

- faster to restore from

- slow process

incremental back up

¬ files created / edited from last back up are copied

- less storage space

- much quicker to create

- full system restore slow

compression software

¬ reduces file size for less disk space used

- need to be extracted before use

encryption software

¬ scrambles data

- stop third parties from accessing

- data decrypted using special key

open source software

- python,

✔ source code provided with software

✔ usually free download

✔ able to edit and distribute changes

✔ social support forums

✔ good for companies with small budgets

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✘ expert needed for debugging

✘ may need additiona support bought

✘ open to malicious code

✘ may take a while to fix

✘ no warranties

propietary software

- windows word

✔ free customer support

✔ professional standards

✔ tailored to market needs

✔ issues more likely to fix quicker

✔ may contain more features

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✘ expensive

✘ rely on one company

✘ not personalised to customers

✘ may be limited updates

network

two or more computers connected together to share information and resources

Local Area Network (LAN)

¬ covers small geographic area

- hardware owned by organisation who use it

- can share resources

- centralised management

- network manager needed

- security issues

- used in schools and homes

Wide Area Network (WAN)

¬ covers large geographical areas

- cables owned by others (BT, Vodafone...)

- connects LANs

- may be town, internet, different countries

cloud storage

¬ stores files and programs online

- infro can be shared

- may need to pay but unlimited

- speed depends on network

- only work on internet

- backup handled by provider (google, dropbox...)

- easier to hack

- google drive, dropbox...

bandwidth

amount of data transferred in a given time

network traffic

badwidth shared so slows network

latency

time delay between sending and receiving

what affects wireless network performance

# distance from Wireless Access Point (WAP

# physical objects (walls)

# interference from other devices

# weather

Wireless Access Point (WAP)

allows devices to connect to WAN using WiFi

router

connects two networks together (LAN and WAN) transmits data between them (packets)

Network Interface Card (NIC)

used to connect device to network by gaining MAC address

ethernet

twisted pair to reduced interference

fibre optic

data transmitted as light , fast but expensive. Longer distance = less interference

switch

connects to devices by getting MAC address to send data to correct device using internal index, reducing data collisions

coaxial cable

single copper wire covered in plastic for insulation with metal mesh to stop interference. Connect tv for freeview

hotspot

location to connect to WAP

WiFi

¬ standard use for wireless networks

- two radio frequencies (2.4GHz / 5GHz)

- split into bands covering small frequency range

- affected by interference from networks using close channels

client server

¬ network managed by a server

- files stored centrally

- stores user profiles, passwords, and access information

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1# clients send request to server

2# processes request and responds

peer to peer

¬ all devices equal

- devices connect directly to each other

- used at home to share files between devices or connect to printer

client server (advantages and disadvantages)

✔ easy to manage network security

✔ easier to track files (central)

✔ servers reliable and always on

✔ easy to update software

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✘ need it specialist to maintain

✘ expensive to set up

✘ may become overloaded if too many clients accessing at once

✘ dependant on server (if server down, clients lose access to work)

peer to peer (advantages and disadvantages)

✔ easy to maintain

✔ not deoendant on server

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✘ no central management

✘ file copies between devices = duplicates

✘ easy to lost track of what stored and which files up to date

✘ if one machine fail = data lost

✘ machines slow if other devices access

internet

worldwide collection of interconnected networks

Uniform Resource Locator (URL)

an address used to access web servers and resources

Domain Name Server (DNS)

a server that stores website domain names and IP addresses (like an address book for them)

domain name

the name of the website (google / youtube...)

hosting

register a unique domain name and pay to place content on webserver

mesh network

¬ devices connected directly to each other

- send data along fastest route

- expensive, lots of cables needed

star network

¬ connected to central switch or server

- device / cable failure doesn't affect rest of network

- easy to add more devices

- better performance

- problem with server affects whole network

- every device needs cable to server

virtual network

¬ software based network

- can exist on same physical network

- Virtual Private Network (VPN) sends data securly over large network (internet)

- has own security (specific login details, firewall)

the cloud

✔ users can access files from any connected device

✔ easily increase storage capacity

✔ no expensive hardware

✔ IT staff not needed

✔ provides security and backups

✔ updated automatically

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✘ need internet connection

✘ dependant on host for security and backups

✘ data vulnerable to hackers

✘ unclear ownership

✘ subscription fees may be expensive

protocol

set of rules how devices communicate and how data is transmitted across a network from start to end and how it should be organised

MAC address

a unique identifier assigned to a device that can't be changed.

- 64 bit binary number

- converted into hexadecimal

Transmission Control Protocol (TCP)

# how devices connect on network

# checks data sent and delivered correctly

# splits data into packets

Internet Protocol (IP)

#responsible for packet switching

Simple Mail Transfer Protocol (SMTP)

# sends emails

# transfer emails between server

Hyper Text Transfer Protocol (HTTP)

# communicate with web servers

# used by web browsers to access websites

Hyper Text Transfer Protocol Secure (HTTPS)

# secure version of HTTP

# encrypts all information sent and received

Post Office Protocol (POP3)

# retrieves emails

# server holds email until downloaded then is deleted

File Transfer Protocol (FTP)

# access, edit and move files

Internet Message Access Protocol (IMAP)

# access emails from server

# copy stays on server until you delete

Layer 1 (Data Link Layer)

# ethernet protocol

- how bits are sent as electrical signal over cables

- passes data over physical network

Layer 2 (Network Layer)

# IP protocol

- used by router

- makes connections between networks

- directs data packets and traffic handling

Layer 3 (Transport Layer)

# TCP protocol

- splitting data into packets

- controlling data flow

- check packets are sent and delivered correctly

Layer 4 (Application Layer)

# HTTP, FTP, SMTP protocols

- turning data into websites and other applications

Packet switching

1# sending device splits data in packets to send across network, each with packet number to show order of data

2# router reads packet header and decides where to direct packet according to IP rules

3# network traffic affects packet path so different routes taken, if too many sent router prioritises

4# packets arrive in wrong order from different journeys, receiving device puts in right order with packet number

5# receiving device checks all packets received, if no then time out message sent

6# receipt sent to sending device if all date there

SQL injection

malicious code inserted into database field on website to corrupt or steal data

phishing

emails or texts from well known companies with links designed to steal money and details

malware

deletes files, lock files, moniter actions, alter permissions, open backdoors

viruses

installed without user knowledge and will replicate

worms

like viruses but self replicate and spread quickly. find weakness in network security

trojans

desguised as software and users install without realising purpose

passive attack

someone moniters data travelling on a network and intercepts sensitive information using packet sniffers

active attack

an attack to a network using malware

insider attack

someone within an organisation exploits their network access to steal information

brute force attack

try to guess passwords and usernames by trial and error by using software to produce likely passwords

denial of service attack (DOS)

a hacker tries to stop users accessing part of a network or website by flooding a network with useless traffic and making it slow and inaccessable

social engeneering

# phishing, over phone

influencing people to give over sensitive information by pretending to be companies over phone

network policy

a set of rules and procedures the organisation follows to ensure their network is safe from attacks and unauthorised access

penetration testing

specialists stimulate potential attacks on their network to identify possible weaknesses

network forensics

investigations to find cause of attacks by having a system of capturing data packets as they enter a network

passwords

prevent unauthorised access by using many characters and a combination of letters numbers and symbols and changing regularly

user access level

which part of the network different groups of people can access, business managers likely to have high access level to access more sensitive data to help prevent insider attacks