computer science year 10 mock

computers built into other devices 

usually control systems- monitor and control

• dedicated to 1 task 
• easy to design
• cheaper to produce
• more efficient

defragmentation 

• files moved, deleted change size, so gaps appear, 
• defragmentation is putting them back together.

volatile memory requires power.

Fetch

• copy memory adress to PC to MDR
• instruction stored in MAR to MDR
• increase PC to point to adress (next instruction)

Decode

• instruction MDR =decoded by CU
• CU prepares for next step

Execute

• instruction performed

Primary storage= memory areas CPU accesses v. quickly, ( RAM/ROM / cache) - fastest read/ write time , mostly volatile.

Secondary storage = non-volatile, all data (OS, apps/user files) stored. 

• Hard Disk Drives-internal storage in PCs.
• stack of magnetised metal disks, spin at 5400-15000 rpm
• data stored magnetically in sectors within tracks. Read write head on moving arm used access sectors
• Portable HDD for backing up large amounts of data.
• V. long lasting + reliable.

SSD's

• no moving parts
• faster
• silent

RAM-if needs extra storage uses virtual memory (v. slow)

ROM- non-volatile, read x write

contains instructiona comp. need to boot up, using Basic Input Output System.

More RAM = faster/smoother system.

GPU's help CPU'S process images

• comp. already have basic ones, but you can upgrade if play games .design software

Optical disks= cheap and robust secondary storage

• CD's ( 700MB), DVD (4.7GB)
• streaming and download services removed need for tehm
• water -proof
• data stored in indentations only laser reads it

Magnetic tapes -archiving + (low cost/GB) =plastic cassettes

power supply- supplies power to motherboard.

case cooling fan- extracts hot air from computer case

CPU heat/cooling sink/ fan -keep CPU at steady temp

CPU =under heat sink 

motherboard- main circuit board, where hardware is connected.

CPU to Var.registers = super quick read/write

prossesing power depends on clock speed/ no. caches /no. cores

CU - fetch decode execute cycle + control flow of data inside + outside CPU

ALU = all calcs. +_/x, logic operations (and/or/not) + binary shifts

• v.fast memory, slower than registers, faster than RAM.
• stores regularly used data, low capacity
• levels: L1=quickest, low capacity/ L2 = slower, mid capacity/ L3= slowest, high capacity.

clock speed

• no. instructions a core carry out/s= Hz. desktop has 3.5 billion Hz.
• higher clock speed, Higher no. instructions /s
• some CPU = overclocked to make run at clock speed = risky CPU could overheat.

high performance cooling systems e.g water cooling needed

multitasking- 4 cores= 4 instructions at once.

larger CPU cache= faster access to CPU to more data to process.

More RAM =faster smoother system

less RAM = slow due to use of virtual memory

Data is sent between networks, in equal sized packets.

Each packet has header( adress (source and destination and number).

Packet's payload= "letter"( part of email,document, web page.)

Include checksum no. =validation, to check hasnt been corrupted.

Packet switching used by routers to direct data packets across internet. 

• sending device splits data into packets, each with packet no. to order data.
• each router reads header, decides which way to send it , according to IP rules.
• way data sent changes on traffic. if router too many packets, prioritise them.
• can arrive in wrong order. recieving device uses packet numbers to put in correct order.
• sometimes packets= missing, recieving devices checks all packets, if not sends timeout message to sending device.
• if all data recieved + checksums match, receipt confirmation sent to sending device

TCP/IP =protocol how data sent between networks.

Transmission Control Protocol (TCP)= sets rules for how devices connect on network, charge of splitting data to packets + reassembling packets, checks data sent and delivered.

Internet Protocol (IP)= responsible packet switching.

HTTP(S)- Hyper Text Transfer Protocol (Secure).- used by web browser to access websites (encrypts all information).

Layer is group of protocols, have similar functions.

Layers = self contained - each layer does job, without need to know what other layers do. Each layer serves layer above it.

Layer 1-Data link layer =passes data over physical network, Layer 2= Network layer- making connections between networks, Layer 3-transport layer-controlling data flow,

Layer 4= Application layer turning data into websites.

• star topologies- all devices connected to centre
• advantages - if device fails, network= unaffected + easy to add more devices, all devices can transmit data at one
• disadvantages - every device needs cable= expensive, if switch fails whole network = affected.
• bus terminal -arranged in a line, connected to sing cabl, devices send data both direction= data collisions.
• ring topology -data moves in one direction, only one device sends data at time + data passes through many devices before reaching destination.
• mesh topology- devices are directly/indirectly connected, so no switch/server. no single point where network can fail. if one device fail, data sent along different route. you can use wirless technology, so removes expense

• = a set of rules for how devices communicate + how data is transmitted across a network.
• protocols cover how communication between 2 devices start + end, how data is organised and what devices do if data goes missing

Communication on the same network uses MAC adresses

• every device need unique identifier so can be found on network.
• MAC adress = assigned to all network-enable devices ( by manufacturer), cannot be changed. also are 48 to 64- bit binary numbers, converted to hexidecimals.

Communication differs between networks using IP adresses 

• IP adresses use when sending data between TCPIP. Unlike MAC adresses, IP isnt linked to hardware assigned mannually (static)/ automatically (dynamic).
• Static = permenant, where companies dont want IP adresses changing, can be v. expensive.
• Dynamic are assigned to device by network server, meaning devices have different IP adresses every time log on. Internet Service Providers use dynamic as = cost-effective and reusable.
• IP addresses =32 /128 bit binary numbers. 128 bit=8 hexidecimal numbers. 32 bit= 4 hexi... no.s.

• Internet= network of networks, its a WAN, based around TCPIP
• www=collection fo website hosted on web servers and accessed through http
• URL's = adresses to access web servers.
• Domain Name Server = translates websites domain name to IP adress.

Cloud uses internet to store files adn applications.

• hosting= business use its servers to store files 
• pros- easy access, no expense for storage hardware, no IT staff, cloud host provides security for you
• cons- easy for hackers, unclear who has ownership over cloud data, subscription fees for using cloud storage and software may be expensive.

Virtual Networks= networks entirely software based, created by partitioning off some physical networks bandwidth to form network.

each has security (firewall), only accessed through certain software or login information.

• passive attack = someone monitors data travelling on network and intercepts sensitive info.
• active attack= someone attacks a network with malware
• insider attack= someon within organisation exploit network access to steal info
• brute force attack= type active attack to gain information by cracking passwords through trial and error, using automated software.
• denial-of-service attack = hacker tries to stop users from accessing a part of network. involve flood network with useless traffic.
• malware = software installed on device without permission, actions = deleting files, scareware,ransomware, spy ware, rootkits.
• asses your files by worms, viruses to emails. trojans.

social engineering = ganing sensitive info by influencing people by telephone, phishing (email, pretending to be well known company.

SQL injections, Structured Query Language. If website SQL code = insecure, easy hackers to get through firewall.

Good network policy will .. test nework for weakness. use passwords /enforce user access levels, install anti_malware. Encrypt sensitive data.

Penetration testing, to stimulate potential attacks on network

Network Forensics- organisation to have system capturing data packets,

password to prevent unauthorised user access network, passwords should be strong, number, letters, symbols.

user access levels- limit no.of people with access to important data.

Anti-malware software - stops malware damaging organisations network.

firewalls to block unauthorised access.

• ethical issues -right or wrong by society
• legal issues - right /wrong eyes of law
• cultural issues - groups of people with particular beliefs/ practices/ languages may be affected/
• enviromental issues= impact natural world.

Stakeholders

• people who are affected by particular scenario (actions of company)
• may be owner/ employees/customers.
• each stakeholder has different priorities which may conflict with own.

when make/use  devices uses lots of energy + natutral resources.

e-waste = big problem (20-50 million tonnes/ year

device manufacturers make it cheaper to replace than repair+ small warranty.

Waste Electric/ Electronic Equipment , rules for disposing e-waste safely. some cut costs send to Africa where laws less strict, most end in landfill, toxic chemicals released

• Copyright Designs and Patents Acts 1988- protect intellectual property
• Copyright covers written/recorded content. Act illegal to share copyrighted files, without permission, use unlincesed software/ plagiarise. Copyright holders make fee to grant permission.
• Patents cover new inventions, protect ideas and concepts.
• Internet makes harder to protect copyrighted content due to file sharing.
• Harder to enforce if content held on servers in different countries/
• Illegal file sharing happens on peer-to -peer networks.

Creative commons allows you to legally share media and software. 

Use to build upon own work 

• Four main types Attribution, - copyrighter credited, work shared.
• Share Alike- modified work only distributed with same license terms,
• Non-commercial- not for profit to use work.
• No deriative work, cannot be modified, but can be copied.

Some in public domain, Uk copyright expires 70 years after creators death.