AS theory

which logic gate doesn’t use two inputs

the NOT gate

what is data redundancy

having multiple copies of data, and depending on purpose, this can be good or bad

how may an AND gate be written

A.B

how may an OR gate be written

A+B

how may a NOT gate be written

Ā

what logic gate is this

a NAND (NOT AND) gate, output is 1 if any output is 0

what logic gate is this

a NOR (NOT OR) gate, output only true when all inputs are false (0)

what logic gate is this

a ZOR (or XOR) gate, for a positive output there can only be one positive input

what gate is 1 when only one input is 1

a XOR gate

0.A=

0

0+A=

1

1.A=

A

1+A=

1

A+A’=

1

A.A’=

0

A.A and A+A=

A

A+ A’.B

A+B

A+A.B

A

A.(A+B)

A

what are kilobytes and what are kibibytes

kilobytes are 1000 bytes and kibibytes are 1024. It goes KB, MB, GB, and TB

what is hexadecimal

base 16, it uses MAC addresses, used in colours and it’s more efficient when representing large binary numbers / are easier for people to read

how do we convert hexadecimal to denary

the most right value is multiplied by 16^0, the next, by 16^1 etc. and are then added together

what are binary coded decimals

when each digit is split and represented as 4 bits

when are binary coded decimals applied

financial calculations as it errors/ ensures accuracy, electronic displays as it’s a visually simpler way of showing bits/ make conversion to and from denary easier, same with storage of date and time in the BIOS

what is 1’s complement

a method of representing signed binary numbers where positives are shown in the standard form, and negatives are produced by inverting each bit of a positive number

what’s two’s complement

the same as one’s complement, but this time a one is added at the end to make arithmetic operations easier

what’s the smallest / largest two’s complement binary number

the smallest is 10000000 and the largest is 01111111

what’s another way of subtracting binaries

adding them and then using two’s complement

what is ASCII and what’s its downside

it consists of 128 characters, each represented by 7 or 8 unique bits and stored in the order of the word, but it’s limited to the Latin alphabet. Note extended ASCII is made up of 256 characters

what’s unicode

essentially a larger version of ASCII, supporting over 150 scripts (i.e. multiple languages), and characters are represented using 8 to 32 bits but it also takes up more space than ASCII

what is an overflow in bits

when the number of bits a register can hold is exceeded, the overflowing bit is normally discarded

what are bitmap images

grids of pixels, each with its own colour and intensity, used in digital photography, web graphics, and desktop applications in formats like JPEG/ PNG

what is colour/ bit depth

the number of bits used to represent the colour of a single pixel/ the number of colours that can be used to represent an image. The higher this is, the better the colour quality

what is a pixel

the smallest part of an image

what is a file header

data stored with the file that contains information about it, like image dimensions, colour depth, and compression type

what is image resolution

the total number of pixels (bits) in an image, typically represented as width x height

what is screen resolution

the (max) number of pixels able to be displayed on screen, it affects how bitmapped images are rendered

how is file size calculated

width of pixels x height of pixels x bit depth if provided. If we want it in bytes rather than bits, this number is divided by 8, then 100 if we further want KB etc.

how is bitmap image quality affected when factors are increased

an increase in pixels makes the image look more detailed, as will increasing image resolution, higher screen resolution means a better display of images (making them sharper/ more detailed), and colour depth allows for a greater range/ accuracy of colour

what happens when factors are decreased in bitmap images

quality is worsened, looking more pixelated , less realistic and can result in banding (visible steps between colours), but file size is smaller

what’s bad about better image quality

more pixels, mean more bits need to be stored, increasing file size. Resolution, however, does not impact file size

what are vector graphics

images created using mathmatical formulas to define shapes, lines, colours etc. they’re commonly used for logos/ illustrations because of their scalability, and in formats like SVG

how do vector images differ from bitmap ones

they are resolution-independent meaning they can be scaled to any size without losing quality, but it requires expensive equiptment

how may vector images be compressed

reducing drawing list properties and removing unused data (?)

what are vector graphics composed of

a drawing list, a group of commands used to define a drawing object and its properties (allowing it to be scalable and not lose quality)

what is a drawing object

a basic element like a shape or line that’s defined mathematically

what is a property

attributes of a drawing object like colour or line thickness

how are sound files recorded and encoded

via an analogue to digital conversion (ADC), which uses sampling. This is where the amplitude of the sound wave is measured at regular intervals, and these sample amplitudes are rounded (quantised) and used to help the computer fill in the rest. This is then encoded, given a binary number, which is saved in sequence

a higher sampling rate / resolution means what

a more accurate version of the sound wave will be represented // less errors will be produced, as more data is recorded, but it will take up more space/ more time to load

what does sampling rate mean

the number of samples taken per second

what does sampling resolution (bit depth) mean

the number of bits used to represent each sample’s amplitude

analogue vs digital data

analogue is continuous sound signals representing vibrations in air pressure, its sound graph is smooth whereas digital data is numerical representations of sound and can be used by digital systems

how do we figure out file size for sound

if it’s in kHZ, multiply it by 1000 to get HZ, which represents bits per second, and then multiply that by the length (in seconds) and the sampling resolution

why is compression needed

high-resolution images can be stored in a smaller size without losing quality and saving storage, data will be transmitted faster (less buffering if a video), and it helps website performance by improving load time, which enhances user experience

what is lossy compression

where data is removed to create a smaller file size and is irreversible. It’s used when data can be lost, like in images or videos

what is lossless compression

where an algorithm is used to reduce file size and is reversible. It’s used when no data can be lost, like in text or software as all data is required, but will generate a bigger file than lossy

what is run-length encoding (RLE)

a form of data compression where consecutive repeated values are stored as a single value, i.e. AAAA would be 4A

how may a sound file be compressed

run length encoding where sounds are grouped (lossless), or removing frequencies outside human range (lossy)

how may an image be compressed

by cropping the image / decreasing the colour depth (lossy) or RLE (lossless)

What's a wide area network

a network that covers a wide geographic scale by combining LANs

what are the pros of using a WAN

wider reach, resources like server databases can be shared, and they’re easy to expand, but it has a low transfer rate

what are some cons of using a WAN

expensive to set up as dedicated lines and routers needed, more complex to manage, weaker security

What's a local area network

networks that cover a small geographical area, like a single building

what are benefits of a LAN

resources can be shared, it’s more secure due to it’s smaller size, it has a high data transfer rate, it has central management

what are some cons to using a LAN

hacking can affect the entire network, it’s harder to manage,the range is limited and it can depend on a single server

what are the benefits of networking computers and devices 

data and resources can be shared (i.e. files or hardware like printers), which reduces cost, it provides better communication/ collaboration (through shared applications), and it increases security as a network manager can oversee networks and apply/ restrict access

what are computer networks made up of

the nodes, transmission data that can be wired (i.e. cables) or wireless (i.e. Wi-Fi), and network devices (like routers/ switches) that allow communication to take place

what are WAPs 

wireless access points, which are devices that allow devices to connect wirelessly to a network/ LAN. Note: because of its limited range, places like airports would need several WAPs to ensure no interruption  

what technology do wireless access points use

spread spectrum technology or infrared

what's a client server 

a server-based network where devices (clients) request information from the main/ central server which then sends the data

what are the pros of using a client server

it has centralised management, it’s easier to manage/ monitor resources or access rights, increasing security, and it ensures data consistency as all clients can access the same data

what are some cons of using a client server

it’s more expensive to set up and maintain, if the server(s) go down, so does the network, and clients are dependent on the server for resources

what's a peer-to-peer model

its a decentralised network type, meaning it has no central server; instead, peers are connected and are of equal status, sharing resources directly.

Note: not good for scenarios with more than 10 devices

what are the cons of a peer-to-peer model

it has weaker security as it’s harder to enforce policies, data consistency is difficult because it’s distributed, and the network’s performance depends on the peers’ capability

what are some benefits of a peer-to-peer model

it’s cheaper to install/ maintain as it doesn’t use a dedicated server; if one peer goes down, the network still works, it’s easier to expand as peers can just join, and no central server increases privacy

what two client types does the client-server model offer 

thin clients and thick clients 

what's a thin client 

A software that relies on a central server to perform tasks and won’t work without one. Most of the processing occurs on a remote server and needs a good/stable connection. e.g. Google docs 

pros of a thin client 

It’s easier/ less expensive as updates/ managements are central, which can offer protection against hacking/ malware, and cheap devices can be used

cons of thin client

high reliance on server - if the server goes down/ break in communication link, devices cannot work, and startup costs are higher than for thick clients 

what can be said about thin clients’ resources

they require minimal local storage

what's a thick client 

a client (device) that does some of the processing itself and the system can work offline or online. It relies heavily on local resources but is more tolerant of a slow network connection. e.g. outlook 

pros of  a thick client

more robust and clients have more control as they can store own data/ files 

cons of a thick client

they're less secure as it relies on clients to keep their own data secure and each client needs to update data/ software individually 

What's a bus network topology 

all devices are connected to a single, central cable. Data only goes one way and terminators are needed at each end to prevent signal reflection.

what are the advantages of a bus network

it's easy to expand, requires little cabling, and if one node fails network continues to function

what are the disadvantages of a bus network 

if main cable fails the whole network goes down, heavy loading decreases performance of network and network is not secure since each packet passes through every node 

how are bus topologies in terms of scalability

it’s less suitable for large networks as collision likelihood is increased while performance is decreased

how are packets sent/ data transmitted in a bus network 

each node looks at packet and determines whether packet address matches its own, leading to potential data collisions and retransmission

what's a star network topology 

where all devices are connected to a central hub or switch, which manages data transmission

what are the advantages of a star network 

it’s easy to add/ remove devices because each device is connected directly to a central switch. The central switch makes the network easy to manage and troubleshoot, lowering collision risk. It’s more secure, and if one connection is broken, it only affects one of the hubs 

what are the disadvantages of a star network  

initial installation costs are high and if central hub/switch fails the whole network goes down 

how are packets handled in a star network if central nod is a switch 

packets are only sent to nodes where the address matches the address in packet.

how are packets handled in a star network if central nod is a hub 

all packets are sent to all device/ node on star network. if address matches it's accepted, if not, it's ignored 

how is data generally transmitted in a star topology

data from any device is sent to the central hub, which routes it to the destination device, reducing likelihood of data collision

how are star topologies in scalability

star topologies are suitable as adding or removing devices is simple and won’t affect the rest of the network. may see this network type in hospitals

what is a mesh topology

A group of devices is connected, creating multiple paths for data transmission (as it can communicate directly or through other nodes), enhancing redundancy and reliability

what are the disadvantages of using a mesh network 

large amount of cabling needed, which is expensive/ time consuming and set up/maintenance is difficult 

what are the advantages of a mesh network 

easy to identify where faults have occured, broken links don't affect other nodes, good privacy/ security and easy to expand 

how are packets handled/ data transmitted in a mesh network 

best route is determined and each packet of data is transferred from the node that recieved it to the node closest to the destination, but it could take several other paths, reducing the chance of network failure, and improving fault tolerance

how are mesh networks in terms of scalability

it’s highly scalable and can handle large amounts of traffic volume but it’s complex and expensive due to it’s extensive cabling / hardware needed