Von Neumman Architecture

Memory

Performance

Magnetic Storage: Greatest storage, lowest cost per GB Not portable, moving parts so damage risk Used by large organisations Comes in plastic cassettes or disks Disk spins around, tracks and sectors are either magentsied (1) or not (0) RW arm over disk (Actuator) to get/set magnetic charge

Optical Storage: Use light to store data, by burning into disk, restart needs a whole layer burnt off Pit = 0, Land = 1 (land has reflection) cheap, portable, little space taken up Slow write speed, damaged/scratched easily, less storage capacity (blu ray up to 50GB)

SSD: Solid State Drives: Non volatile flash memory used Fast RW times, durable as no moving parts More expensive than magnetic disks but same storage Electrons either charged/trapped (0) or not (1)

Binary is Base 2 8-bit numbers (0 and 1) B->D: Make a table: 128|64|32|16|8|4|2|1 and then write 0 and 1 values underneath then add D->B: make table and go from left to right subtracting numbers, eg 79 would be 64,7,4,2,1 to get to 0.

Binary Addition: 1+1 = 0 carry 1 1+1+1 = 1 carry 1 you can get overflow of most significant value, and loss of data

Binary Shifts: Left Shift multiplies x2 each time its shifted (so 3 shifts is 2x2x2 = 8) Right shift divides by 2 each shift When calculating, fill gaps with 0s

Hexadecimal: 1-9 = 1-9, 10-15 = A-F H->D: 87 = 8x16 + 7x1 when you make table : 16|1 D->H: 106: 106/16 = 6 r 10 = 6A H->B: turn hex to denary then use tables: 8|4|2|1 8|4|2|1 B->H: use tables: 8|4|2|1 8|4|2|1 to get denary then turn to binary

Characters: Character sets are collections of characters that a computer recognises from their binary representation Eg Ascii

Storing Images: Images stored as Pixels Number of colours in an image = number fo bits So B&W will have 1 bit, either 0 or 1 so 2 colours 2 bit image = 00,01,11,10 so 4 colours Total number of colurs = 2 to the power of n, (n=bits per pixel, bpp) File size (in bits) = image resolutuion (widthxheight) x colour depth Metadata is data about data

Storing Sound: recorded by a microphone as analogue, continually changing. Digital is read by computers, sodata is converted by an analouge to digital converter (ADC), this processs is called sampling Digital accuracy can be improved 9matched closer to analogue) by increasing sample rate (taking samples more regularly) File size = sample rate (Hz) x bit depth x length higher sample rate = bigger file size

Compression: Smaller files take up less storage, streaming quiker (less bandwidth needed), web pages load quicker

LAN: local area network spans a small geographical area less than a mile. Infrastructure owned by organisation, relatively cheap WAN: Wide area network, connects LANS (internet). businesses would hire organisations to wire it, too expensive otherwise. WAN connected by satelite/ radio links, telephone lines

Factors affecting Network Performance: Bandwidth: the amount of data that can be transferred in a given time Wired wuicker than wireless, wirelesss depends on range +signal quality

Hardware: NIC allows device to connect to a network Switches connect devices on a lan Routers transmit data between networks Wired ethernet connections (Cat 5e and 6) are twisted pair of 4 copper wires. fibre optic cables transmit light. high performance and expensive Blutooth is a direct connection between 2 devices, 10m range so used for headphones Wi-Fi Can be used by many devices connected to a LAN at the same time. 40m-100m range so used in homes. Higher bandwidth vs BT

Client-Server Model Managed by a server, files/software stored centrally Clients send requests to server, server responds Easy to keep track of files, easy to backup, easy to manage network security, reliable and always on servers Expensive, need IT specialist, server dependant, server can become overloaded

Peer-to-Peer Model Networks are equal, connect directly (no server) Store files on individual devices rather than server Easy to maintain, no server dependance No centralised management, copying files creates duplicates, peer machines are less reliable as data is lost if one fails, machines slow down when other devies cross them, harder to do backups

The Internet: Domain Name Server (DNS) translates websites domains names into IP addresses so we dont need to remember Ip addresses

Star Topology: All devices connected to central switch/server If one device fails, ret of network is unaffected. better peformance as data goes straight to a central device, few data collisions (unlike bus topology)

Mesh Topology: Decentralised, all deviced connected to each other. No single point of network failure, if a network fails, data takes different route Partial mesh: not all devices fully connected Both expensive, used in the army

A network protocol is a set of rules used to govern communication and is therefore used to define rules for data transmission over a network (eg speed of transmission)

Addressses MAC: 16 bit chunks separated by a colon (:) IPV4 uses 32 bits, so 4 billion adresses, IPV6 has 128 bits

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Attack types: Passive: someone moniters data, using packet sniffers Active: someone attacks with malware Insider attack: Someone in an organisation exploits their network access Brute force attack: USe automated software to trial and error passwords Denial of service attack (Dos): hacker floods derver with useless info. making network slow DDoS: distributed DDos, many hackers, infect computers which are then called "zombies" SQL Injections: when a malicious SQL query (command) is entered into a data input box, insecure websites will allow access to private info.

Malware types: Scareware - scares owner Ransomware: encypte=s files unless large money sum is payed Spyware: Records users key strokes Viruses attatch by copying themsleves to files Worms attatch by self replicating, spread quickly Trojans are malware desquised as legitimate software.

People are often easy targets, hackers call them to get access by tricking them, or phishing emails. Can spot by anti-fishing, or grammar checing as they are often poorly written

Safety: Organisations should: regularly test the network, use passwords, install antimalware and firewalls, encyption

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