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components of a computer system Flashcards

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1
Q

what is the purpose of a computer?

A
  • to take data, process it, then output it, and doing this more efficiently than humans.
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2
Q

what does a computer system consist of?

A
  • consists of hardware and software that work together to process data / complete tasks.
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3
Q

what is hardware?

A
  • the physical stuff that makes up your computer system, like the CPU, motherboard, monitor and printer.
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4
Q

what is software?

A
  • the programs or applications that a computer system runs e.g. an OS, a word processor or video game.
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5
Q

what are peripherals?

A
  • external pieces of hardware like the keyboard, mouse and printer.
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6
Q

what are the different types of computer system?

A
  • general purpose: designed to perform many tasks like PC’s and tablets.
  • dedicated systems: designed for one particular function like controlling traffic lights or an aeroplane.
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7
Q

what are embedded systems?

A
  • computers built into other devices, like dishwashers, microwaves and TV’s.
  • usually dedicated systems.
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8
Q

what is the purpose of embedded systems?

A
  • usually used as control systems (monitor and control machinery in order to achieve a desired result).
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9
Q

embedded vs. general

A
  • embedded systems are dedicated to a single task so are usually easier to design, cheaper to produce and more efficient at doing their task than a general purpose computer.
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10
Q

what are the main hardware components of a computer and what do they do?

A
  • power supply: supplies power to motherboard, optical and hard drives, and other hardware.
  • case cooling fan: extracts hot air from the computer case.
  • CPU heat sink and cooling fan: keeps CPU at steady temperature as they generate a lot of heat.
  • CPU (under heat sink): does all processing and is most important component.
  • graphics card.
  • motherboard: main circuit board in computer, where the hardware is connected.
  • hard disk drive: internal secondary storage.
  • RAM sticks: computer memory.
  • optical drive: for read/writing of optical disks.
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11
Q

what is the purpose of the CPU?

A
  • processes all of the data and instructions that make a system work, and carries them out.
  • is the brain of the computer system.
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12
Q

what are the main components of the CPU?

A
  • the control unit (CU).
  • the arithmetic logic unit (ALU).
  • the cache.
  • various registers.
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13
Q

what does CPU stand for?

A
  • central processing unit.
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14
Q

what does the CU do?

A
  • in overall control of the CPU.
  • main job is to execute program instructions by following the fetch-decode-execute cycle.
  • controls flow of data inside the CPU (to registers, ALU, cache) and outside CPU (to main memory and input/output devices).
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15
Q

what does the ALU do?

A
  • does all calculations (simple addition and subtraction, compares size of numbers and can do multiplications and divisions using repeated addition and subtraction).
  • performs logic operations such as AND, OR and NOT and binary shifts.
  • contains accumulator register.
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16
Q

what is cache?

A
  • very fast memory in the CPU.
  • slower than registers but faster than RAM.
  • stores regularly used data so CPU can access it quickly when next needed (when CPU requests data, it checks cache first to see if data is there, else, it fetches it from RAM).
  • very low capacity and expensive compared to RAM and secondary storage.
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17
Q

what are the different levels of cache memory?

A
  • L1 is quickest but has lowest capacity.
  • L2 slower but can hold more.
  • L3 slower but can hold more.
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18
Q

what are registers?

A
  • in CPU, and temporarily hold tiny bits of data needed by CPU.
  • super quick to read/write to (way quicker than any other form of memory).
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19
Q

what is Von Neumann architecture?

A
  • describes a system where the CPU runs programs stored in memory.
  • programs consist of instructions and data which are stored in memory addresses.
  • came up with his design in 1945.
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20
Q

what are the features of Von Neumann architecture?

A
  • program counter (PC) in CU.
  • accumulator in ALU.
  • registers: memory address register (MAR) and memory data register (MDR).
  • only uses one memory for both the data and the instructions.
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21
Q

what is the PC?

A
  • holds memory address of the instruction for each cycle.
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22
Q

what is the accumulator?

A
  • stores intermediate results of calculations in the ALU.
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23
Q

what is the MAR?

A
  • holds any memory address about to be used by the CPU.

- the address might point to data or a CPU instruction.

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24
Q

what is the MDR?

A
  • holds the actual data or instruction, which may have been fetched from memory, or be waiting to be written to memory.
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25
Q

how does the CPU run?

A
  • fetch-decode-execute cycle.
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26
Q

what is the fetch instruction?

A

1) copy memory address from PC to the MAR.
2) copy instruction stored in the MAR address to the MDR.
3) increment (increase) the PC to point to address of next instruction ready for the next cycle.

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27
Q

what is the decode instruction?

A

1) the instruction in the MDR is decoded by the CU.

2) CU may prepare for next step e.g. loading values into the MAR or MDR.

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28
Q

what is the execute instruction?

A

1) instruction is performed, which could be: load data from memory, write data to memory, do a calculation or logic operation (using ALU), change the address in the PC, or halt the program.

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29
Q

what affects CPU performance?

A
  • clock speed.
  • number of cores.
  • cache size.
  • however, by increasing the above, the CPU will be more expensive.
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30
Q

how does clock speed affect CPU performance?

A
  • this is number of instructions a single processor core can carry out per second (Hz), usually 3.5 GHz.
  • higher clock speed = greater number of instructions that can be carried out per second.
  • some CPU’s can be overclocked to make them run faster than the factory-set rate but is risky (CPU can overheat, causing crashes or permanent damage to the system so high performance cooling systems (e.g. water cooling) usually needed.
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31
Q

how do the number of cores affect CPU performance?

A
  • each core in a CPU can process data independently so more cores = more instructions can be carried out at once.
  • PCs and smartphones have 4 or more cores usually.
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32
Q

how does cache size affect CPU performance?

A
  • larger CPU cache gives the CPU faster access to more data it needs to process.
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33
Q

what is the difference between RAM and ROM?

A
  • ROM is non-volatile and RAM is volatile.

- ROM can only be read, RAM can be read and written to.

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34
Q

what is the purpose of ROM in a computer system?

A
  • ‘read only memory’.
  • can only be read, not written to.
  • comes on small, factory-made chip built into mother board.
  • contains all instructions a computer needs to boot up properly. these instructions are called BIOS (Basic Input Output System).
  • as soon as computer is powered on, CPU reads instructions from ROM. this tells CPU to perform self checks and set up the computer.
  • often use flash memory.
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35
Q

what is the purpose of RAM in a computer system?

A
  • ‘random access memory’
  • can be read and written to.
  • when computer boots up, OS is copied from secondary storage to RAM.
  • when software applications, documents and files are opened, they are copied from secondary storage to RAM. they stay in RAM until files or applications are closed.
  • RAM slower than CPU cache but way faster than secondary storage.
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36
Q

what does volatile mean?

A
  • temporary memory.

- requires power to retain its data.

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37
Q

what does non-volatile mean?

A
  • permanent memory.

- keeps contents even when it has no power.

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38
Q

what is virtual memory?

A
  • computers have limited amount of RAM, so when it fills up, the computer needs somewhere else to put its application data (moves recently unused data to location on secondary storage called virtual memory).
  • may be needed if too many apps open at once or if a particularly memory-intensive app is being used.
  • if CPU needs to read data stored in virtual memory, it must move back to RAM (slow data transfer/ to respond as constantly switching between virtual memory and RAM).
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39
Q

what is flash memory?

A
  • non-volatile memory that stores data in electrical circuits by trapping electrons.
  • used in ROM, SD cards, USB sticks, SSDs. SD cards and USB sticks are solid-state storage, but are much slower than SSDs and have a much shorter read/write life.
  • used to expand storage capacity of small devices like cameras, smartphones and tablets which are too small for SSDs and HDDs. their capacity is very high relative to their tiny size.
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40
Q

how can you improve system performance?

A
  • more RAM so less virtual memory used (so can run more apps/memory-intensive applications). just have to replace RAM sticks with higher capacity/speed ones.
  • GPUs (graphic processing units) are specialised circuits for handling graphics and image processing (relieve processing load on CPU).
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41
Q

what is secondary storage?

A
  • non-volatile.
  • where all data (OS, applications, user files) stored when not in use.
  • includes: magnetic hard disk drives, solid state drives, CDs and SD cards.
  • read/write speeds are much slower compared to primary storage.
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42
Q

what is primary storage?

A
  • refers to memory areas that the CPU can access very quickly eg. CPU registers, cache, ROM and RAM.
  • has fastest read/write speeds and is mostly volatile.
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43
Q

what are magnetic hard disks?

A
  • traditional internal storage in PCs and laptops
  • made of a stack of magnetised metal disks spinning at a rate of between 5400 and 15000 rpm (revolutions per minute).
  • data is stored magnetically in small area called sectors within circular tracks. Read/write heads on a moving arm are used to access sectors on the disk.
  • generally very long lasting and reliable, but can be damaged by large impacts eg. dropped.
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44
Q

what are solid state drives(SSDs)?

A
  • storage devices with no moving parts. most are a type of flash memory, and are used for internal storage.
  • faster read/write times than HDDs -> much quicker booting up time and opening programs and files.
  • portable SSDs can be used to back up and transport data.
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45
Q

what are hybrid drives?

A
  • use solid state storage for the OS and programs, and hard disk for data.
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46
Q

HDDs vs SSDs

A
  • HDDs are cheaper, have higher capacity, longer read/write life (SSDs can only been written a certain number of times before they begin to deteriorate).
  • SSDs are faster, don’t need defragmenting, more shock-proof, silent (HDDs make some noise).
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47
Q

what are optical discs?

A
  • CDs(can hold 700MB), DVDs(can hold 4.7GB) and Blu-Ray discs(can hold 25GB).
  • data is stored as microscopic indentations on the shiny surface of the disc, and is read by shining a laser beam on the surface and detecting changes in the position of the reflected beam.
  • come in 3 forms: read-only(eg. CD-ROM), write-once(eg.CD-R), rewritable(eg. CD-RW)
  • use is declining: streaming and download websites on the internet, modern devices don’t have optical drives.
  • very cheap(per GB), portable, won’t be damaged by water or shocks, but are easily scratched.
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48
Q

what are magnetic tapes?

A
  • used for archiving by large organisations in archive libraries to store large amounts of data frequently.
  • much greater storage capacity than HDDs and extremely low cost per GB.
  • come in plastic cassettes which require a specific tape-drive for read/writing.
  • tape is read/written sequentially (from beginning to end or until stopped by computer), so very slow when finding specific data stored on it, but has a fast read/write speed once it is in the correct place to begin reading/writing.
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49
Q

average cost per GB (priciest first)

A
  • SSD
  • memory card
  • HDD
  • optical disc
  • magnetic tape
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50
Q

average read/write speed (fastest first)

A
  • SSD
  • HDD
  • magnetic tape
  • memory card
  • optical disc
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51
Q

average capacity (highest first)

A
  • magnetic tape
  • HDD
  • SSD
  • memory cards
  • optical disc
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52
Q

what are the 2 types of networks?

A
  • LAN (local area network)

- WAN (wide area network)

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53
Q

what is a LAN?

A
  • local area network.
  • covers a small geographical area located on a single site eg. schools, businesses, unis.
  • all hardware is owned by the organisation that uses it.
  • either wired (eg. Ethernet cables) or wireless (using WiFi)
  • lots of homes have a LAN to connect various devices eg. PCs, tablets, smart TVs and printers.
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54
Q

why use a LAN?

A
  • sharing files is easier (network users can access the same files, work collaboratively on them and copy files between machines).
  • can share same hardware (eg. printers)
  • internet connection can be shared between every device.
  • can communicate with LAN users cheaply and easily (eg. instant messaging)
  • user accounts can be stored centrally, so users can log in from any device on the network.
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55
Q

what is a WAN?

A
  • wide area network.
  • connects LANs that are in different geographical locations eg. a business with offices in different countries would need a WAN for all their devices to connect together.
  • organisations hire infrastructure (eg. communication lines) from telecommunications companies, who own and manage the WAN, as a WAN is much more expensive to set up than a LAN.
  • may be connected using fibre or copper telephone lines, satellite links or radio links.
  • the internet is the biggest WAN.
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56
Q

what factors affect the performance of networks?

A
  • bandwidth (amount of data that can be transferred in a given time eg. 500 Mbps - megabits per second). greater bandwidth = better performance.
  • available bandwidth shared between users of a network so too many users or heavy use (eg. streaming video) may cause congestion and slow the network, so can limit bandwidth available to individual users to address this.
  • wired connections are generally faster and more reliable than wireless. fibre optic cables give much better performance than copper cables. wireless performance depends on signal quality so is affected by the range of the device, amount of interference from other devices, and physical obstructions like thick walls.
  • choice of hardware and network topology also have a big effect.
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57
Q

what are client-server networks?

A
  • managed by a server and the devices connected to the server are clients.
  • files and software usually stored centrally on server rather than on individual client devices.
  • clients send requests to server, the server processes the request and responds. this is the client-server relationship.
  • server stores user profiles, passwords and access information, so may request a password before fulfilling certain requests or deny requests to users without right access level.
  • most internet work on client-server relationship eg. websites hosted on web servers. web browsers are client programs which send requests to web servers, which fulfill requests for thousands of clients.
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58
Q

pros and cons of client-server networks

A
  • PROS: easier to keep track of files as they are centrally stored, easier to perform backups, easier to install and update software, easier to manage network security (eg. anti-malware software and user access levels), servers are very reliable and are always on.
  • CONS: expensive to set up and needs IT specialists to maintain the network and server. server dependence (if server goes down all clients lose access to work). server may become overloaded if too many clients are accessing it at once.
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59
Q

what are peer-to-peer (P2P) networks?

A
  • all devices are equal, connecting directly to each other without a server.
  • you store files on individual devices and share them with others.
  • may use at home to share files between devices, or connect devices to a printer.
  • some P2P networks on the internet like video calling (Skype) and file sharing (usually illegal sharing of copyrighted material).
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60
Q

pros and cons of P2P networks

A
  • PROS; easy to maintain (don’t need expertise or expensive hardware). no dependence on server (if one device fails the whole network isn’t lost).
  • CONS: no centralised management (devices need their updates and security installed individually) backups are more complicated. copying files between devices creates duplicate files (easy to lose track of what’s stored where and which files are up-to-date). peer machines are less reliable and data may be lost if one fails. machines are prone to slow down when other devices access them.
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61
Q

what hardware can be used to connect devices to LAN?

A
  • NICs, switches, routers, wireless access points, transmission media(cables and radio waves/wireless).
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62
Q

what are NICs?

A
  • network interface controllers are internal pieces of hardware that allows a device to connect to a network.
  • can be used on separate cards, but nowadays they are built into the motherboard.
  • exist for both wired and wireless connections.
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63
Q

what are switches?

A
  • connect devices to LAN. they receive data (in units called frames) from one device and transmit this data to the device on the network with the correct MAC address.
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64
Q

what are routers?

A
  • responsible for transmitting data between networks (always connected to at least 2 networks).
  • have a crucial role on the internet, directing data (in units called packets) to their destination.
  • used in homes and offices to connect LAN to internet.
  • home routes are actual routers, switch and WAP all-in-one.
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65
Q

what are the different cables?

A
  • ethernet cables connect devices in a LAN (eg. CAT 5e or CAT 6). they are ‘twisted pair’ cables, containing 4 pairs of copper wires which are twisted together to reduce internal interference.
  • coaxial cables are made of a single copper wire surrounded by a plastic layer for insulation and a metallic mesh which provides shielding from outside interference.
  • fibre optic cables transmit data as light. they are high performance and therefore expensive cables, as they don’t suffer interference and can transmit over very large distances without loss of signal quality.
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66
Q

how does a wireless connection work?

A
  • use radio waves to transmit data.
  • to set up a wireless network, you need a wireless access point (WAP) device. a WAP is basically a switch that allows devices to connect wirelessly.
  • hotspots -> locations where you can connect to a WAP.
  • to connect, devices need wireless capability, which is usually built-in, but if not, use a USB dongle. HDMI dongles are popular for TVs.
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67
Q

how does Wi-Fi work?

A
  • uses two radio frequency bands (2.4 GHz and 5 GHz). 2.4 GHz has a greater range and is better at getting through walls and other obstructions, while 5 GHz is faster over short distances.
  • the bands are split into numbered channels that each cover a small frequency range. the channels in 2.4 GHz band overlap.
  • performance affected by interference between networks using adjacent channels. To avoid problems, only certain channels that are spaced apart tend to be used. the 5 GHz band has more non-overlapping channels than the 2.4 GHz band, so there is less chance of interference.
  • the data is encrypted.
68
Q

what is the internet?

A
  • the internet is a network of networks (WAN which connects devices and networks from all over the world).
  • based around the protocol TCP/IP.
69
Q

what is the world wide web?

A
  • the world wide web (www) is a collection of websites that are hosted on web servers and accessed through the http protocol.
70
Q

what are URLs?

A
  • addresses used to access web servers and resources on them.
71
Q

what is a domain name server (DNS)?

A
  • translates a website’s domain name (eg. www.bbc.com) into its IP address.
  • the internet has a network of domain name servers, meaning you don’t need to remember IP addresses to access websites, you can use domain names instead.
72
Q

what is hosting?

A
  • when a business uses its servers to store files of another organisation.
  • the traditional use for this on the internet is the hosting of websites.
  • a relatively recent use of internet hosting is for general storage of user files and also providing online software - cloud computing / ‘the cloud’
73
Q

what is the cloud?

A
  • a relatively recent use of internet hosting is for general storage of user files and also providing online software - cloud computing / ‘the cloud’
  • acts like an extension of a traditional client-server network where user files are stored centrally on a network server.
74
Q

pros and cons of the cloud

A
  • PROS: users can access files from any connected device, easy to increase how much storage is available, no need to by expensive hardware to store data, no need to pay IT staff to manage hardware, cloud host provides security and backs up for you, cloud software will be updated automatically.
  • CONS: need connection to the internet to access files, dependent on host for security and back-ups, data in the cloud can be vulnerable to hackers, unclear who has ownership over cloud data, subscription fees for using cloud storage and software may be expensive.
75
Q

what are virtual networks?

A
  • a network that is entirely software-based.
  • created by partitioning off some of a physical network’s bandwidth to form a separate network.
  • several virtual networks can exist on the same physical network. these networks all share the same hardware, making virtual networks more efficient than standard physical networks.
  • each virtual network has its own security, including its own firewall, so can only be accessed by using certain software or login information (other people could be using the same physical network and not have access to the virtual network, or even know it exists).
76
Q

what are virtual private networks?

A
  • VPNs are a type of virtual network that can be used to send data securely over a large network, like a WAN or the internet eg. between 2 offices on different sites, or to set up a school intranet that all students can access from home.
77
Q

what is a virtual LAN?

A
  • allows you to split a LAN into several separate networks using the same hardware.
78
Q

what is a star network topology?

A
  • all the devices are connected to a central switch or server that controls the network.
  • the central switch allows many devices to access the server simultaneously.
  • may be wired or wireless.
79
Q

pros and cons of a star topology

A

PROS: if one device fails or a cable is disconnected, the rest of the network is unaffected. simple to add more devices to the network. better performance than other setups (data goes straight to central device so all devices can transmit data at once unlike ring network, and very few data collisions, unlike bus network).
- CONS: in wired networks, every device needs a cable to connect to the central switch or server, which can be expensive eg. office with 50 terminals. if there is a problem with the switch or server then the whole network is affected.

80
Q

what is tertiary storage?

A
  • used for long term data storage.

- mainly used for archives and back-ups of massive amounts of data.

81
Q

what are traditional network setups?

A
  • bus topology: all devices arranged in a line connected to a single backbone cable. devices send data in both directions which can cause data collisions, slowing the network.
  • ring topology: data moves in one direction around the ring preventing collisions, but only one device can send data at a time and data passes through many devices before reaching its destination.
82
Q

what is a mesh network topology?

A
  • relatively new network layout.
  • decentralised -> networking devices are either directly (full mesh topology) or indirectly (partial mesh topology) connected to every other one without the need for one central switch or server.
  • work by sending data along the fastest route from one device to another.
83
Q

pros and cons of mesh topologies

A
  • PROS: no single point where where network can fail (if one device fails, data sent along different route).
  • very expensive (need a lot of wire to connect so many devices together), but now people are using wireless technology, so mesh networks are a more practical option.
84
Q

what is ethernet?

A
  • network protocol used on LANs.
85
Q

what is a protocol?

A
  • set of rules for how devices communicate and how data is transmitted across a network.
  • cover how communication between two devices should start and end, how the data should be organised, and what the devices should do if the data goes missing.
86
Q

what are MAC addresses?

A
  • used for communication on the same network.
  • every device needs a unique identifier so it can be found on a network, so MAC addresses are assigned to all network-enabled devices by the manufacturer.
  • unique to the device and cannot be changed.
  • 48 or 64-bit binary numbers, and to make them easier to use, they’re converted to hex.
  • mainly used by Ethernet protocol on LANs. LAN switches read the MAC addresses and use them t direct data (sent in frames) to the right device.
87
Q

what are IP addresses?

A
  • used for communication between different networks.
  • used when sending data between TCP/IP networks eg. over the Internet.
  • aren’t linked to hardware. are assigned either manually (static) or automatically (dynamic) before the device can access the network.
  • can be either 32 or 128-bit binary number, depending on the IP version you are using. 32 -> converted into 4 denary numbers. 128 -> converted into 8 hex numbers.
  • the data is sent in packets and directed by routers using IP addresses.
88
Q

static vs. dynamic IP addresses

A
  • static IP addresses are permanent addresses. they’re used to connect printers on a LAN, and for hosting websites on the Internet (companies don’t want their IP address changing). static IP addresses on the Internet can be very expensive.
  • dynamic IP addresses are assigned when a device logs on to a network, meaning that it may have a different address every time it connects. Internet Service Providers (ISPs) commonly use dynamic IP addresses ad they are more cost effective and can be reused.
89
Q

what are the different protocols?

A
  • TCP/IP (most important)
  • HTTP
  • HTTPS
  • FTP
  • POP3
  • IMAP
  • SMTP
90
Q

what is TCP/IP?

A
  • protocol which dictates how data is sent between networks eg. over the internet. it is made up of two protocols.
  • TCP (transmission control protocol) sets rules for how devices connect on the network. it’s in charge of splitting data into packets and reassembling the packets back into the original data once they reach the receiving device. it’s also responsible for checking the data is correctly sent and delivered.
  • IP (internet protocol) is responsible for packet switching.
91
Q

what is the HTTP protocol?

A
  • hyper text transfer protocol.

- used by web browsers to access websites and communicate with web servers.

92
Q

what is the HTTPS protocol?

A
  • HTTP Secure.

- a more secure version of HTTP. it encrypts all information sent and received.

93
Q

what is the FTP protocol?

A
  • file transfer protocol.
  • used to access, edit, and move files between devices on a network, eg. to access files on a server from a client computer.
94
Q

what is the POP3 protocol?

A
  • post office protocol version 3.
  • used to retrieve emails from a server. the server holds the email until you download it, at which point it is deleted from the server.
95
Q

what is the IMAP protocol?

A
  • internet message access protocol.
  • used to retrieve emails from a server. the server holds the email until you actually delete it (you only download a copy).
  • used by most web-based email clients.
96
Q

what is the SMTP protocol?

A
  • simple mail transfer protocol.

- used to send emails and also used to transfer emails between servers.

97
Q

what are layers?

A
  • group of protocols which have similar functions.
  • are self-contained (protocols in each layer do their job without needing to know what’s happening in the other layers).
  • each layer serves the layer above it (does hidden work needed for an action on the layer above eg. when you send an email on layer 4, this triggers actions in layer 3, then layer 2, and then layer 1).
  • data can only be passed between adjacent layers.
98
Q

what occurs in layer 4?

A
  • aka application layer.

- protocols cover: turning data into websites and other applications and vice versa eg. HTTP, FTP, SMTP.

99
Q

what occurs in layer 3?

A
  • aka transport layer.
  • protocols include: controlling data flow eg. splitting data into packets and checking packets are correctly sent and delivered eg. TCP.
100
Q

what occurs in layer 2?

A
  • aka internet layer.
  • protocols include: making connections between networks, directing data packets and handling traffic. used by routers eg. IP.
101
Q

what occurs in layer 1?

A
  • aka link layer.
  • protocols include: passing data over the physical network. responsible for how bits are sent as electrical signals over cables, wireless and other hardware eg. Ethernet.
102
Q

what are the advantages of using layers?

A
  • breaks network communication into manageable pieces. this helps developers concentrate on only one area of the network without having to worry about the others.
  • as layers are self-contained, they can be changed without the other layers being affected.
  • having set rules for each layer forces companies to make compatible, universal hardware and software, so different brands will work with each other and always work in basically the same way.
103
Q

what are data packets?

A
  • data sent between networks, eg. on internet using TCP/IP, is split into equal-sized packets.
  • each packet has a header, containing control information (which includes the packet’s destination address, source address and packet number).
104
Q

what is the data packet’s payload and checksum number?

A
  • the data packet’s payload is the thing a person is likely to read eg. part of an email, document, web page or streamed video.
  • checksum number -> form of validation used to check that the payload data hasn’t been corrupted during transit. the sending and receiving devices both calculate a checksum value by performing a function on the payload data. if the values match then the data has been received correctly.
105
Q

what is packet switching?

A
  • used by routers to direct data packets on the Internet and other IP addresses.
  • the sending device splits the data into packets to be sent across the network. each packet is given a packet number to show the order of the data.
  • each router reads the packet header and decides which way to send the packet next, according to the IP rules.
  • the way the data is sent changes depending on network traffic so the packets can take different routes. if a router receives too many packets at once it may prioritise some over others.
  • as the packets take different routes, they can arrive in the wrong order. the receiving device uses the packet numbers to reassemble them in the right order.
  • if all the data is received and the checksums match, a receipt confirmation is sent to the sending device.
106
Q

what happens if packets go missing?

A
  • sometimes packets go missing in transit so the receiving device checks periodically that all the packets have been received. if it hasn’t been received in a certain time, it sends a timeout message back to the sending device.
107
Q

pros of packet switching

A
  • efficient use of the network as there are so many routes that data can take (packets can reach their receiving device even if there’s heavy traffic).
108
Q

what is a system software?

A
  • software designed to run and maintain a computer system.

- most important is the OS, and there is also the utility software.

109
Q

what is the OS including the main functions?

A
  • operating system.
  • complex piece of software found on most computer systems.
  • main functions: provide a user interface (allowing a user to interact with the computer and vice-versa), provide a platform for different applications, allow the computer to multi-task by controlling memory resources and the CPU, deal with file management and disk management, manage system security and user accounts.
110
Q

what is a user interface(OS)?

A
  • allows users to interact with a computer system.
  • GUI (graphical user interfaces) are most common: designed to be easy for everyday users by making the visual, interactive and intuitive.
  • GUIs are optimised for specific input methods. in the past, they have been WIMP-based (windows, icons, menus and pointer). iOS and Android were created for touchscreen devices, using finger gestures in place of a mouse.
  • a command-line interface is text based. the user enters specific commands to complete tasks. command-line interfaces are less resource-heavy than GUIs, but aren’t suitable for everyday users. however, for advanced users, they can be more powerful and efficient than a GUI. they can be used to automate processes using scripts (simple programs).
111
Q

what are device drivers and peripheral management(OS)?

A
  • OS uses device driver software to communicate with internal hardware or peripherals connected to the computer system.
  • every piece of hardware connected to the computer system requires a device driver, which act as translators for the signals between the OS and hardware.
  • when a computer is booted up, OS will choose the correct device drivers for the hardware it detects. if new hardware is connected to the computer, the system will install the new, matching driver.
  • driver manufacturers may release updates to device drivers in order to fix bugs, add features or improve the performance of their hardware. updates may be installed automatically by the OS or manually by the user.
112
Q

what is memory management/multi-tasking(OS)?

A
  • OS provides a platform to run applications (by configuring hardware so they can use it, and giving access to the CPU and memory).
  • operating systems that can run multiple applications at the same time are called multi-tasking OSs.
  • the OS helps the CPU carry out multi-tasking by efficiently managing memory and CPU processing time: when app opened, OS moves necessary parts to memory, followed by additional parts that aren’t required. the OS decides if applications or features have been used recently - if not, they may be removed from memory.
  • to run multiple applications, OS makes sure the applications don’t overwrite or interfere with each other. a memory manager allocates certain applications certain memory addresses, to make sure their processes are placed into separate locations.
  • only one application is processed by the CPU at a time, so the other processes must wait. OS divides CPU processing time between open applications and my prioritise certain processes in order for instructions to be executed in the most efficient order.
  • when required, OS organises the movement of data to-and-from virtual memory.
  • it seems like many applications are processed at the same time, but in reality, the CPU switches between each one extremely quickly.
113
Q

how does the OS deal with user accounts?

A
  • OS may be single-user(eg. Windows 10 and OS X - one user to use the computer at once) or multi-user (eg. UNIX sever - allow several users to use the computer at the same time). multi-users OSs are often used on mainframes (huge supercomputers) and give many users simultaneous access eg. ATMs allow thousands of people access to large bank’s mainframe at the same time.
  • OS responsible for user account control. user accounts allow different users to be granted access to specific data or resources on a computer system. on most desktop OSs, each user has access to their own personal data and desktop or resources on a computer system, but can’t access other users’ personal data.
  • OS may have anti-theft measures to prevent other users from accessing locked devices or accounts to steal information. user accounts may be password or pin protected. some devices also require a user to draw a specific patter on a screen or have fingerprint or retina scanners.
114
Q

what is file and disk management(OS)?

A
  • computers store data as files. images, music, videos and spreadsheets are all just collections of data. file extensions (eg. .jpg, .mp3, .mpeg) tell the computer which software should be used to open the file.
  • file management: organisation of data into a usable hierarchical structure. it also deals with movement, editing and deletion of data.
  • OS manages hard disk. it splits physical disk into storage sectors, decides which sectors to write data to, and keeps track of free space on the disk. ideally, the data for a single file would be placed in adjacent sectors, but this isn’t always possible.
  • the OS also organises and maintains the hard disk with utility software eg. defragmentation software.
  • utilities like file explorer allow users to navigate and edit file structure or access their files.
115
Q

what is utility system software?

A
  • helps maintain or configure a computer. many are installed with the OS, but extra utility software can be installed to perform additional tasks.
  • eg. defragmentation utilities, backup utilities, compression software and encryption software.
116
Q

what are defragmentation utilities?

A
  • files are stored on a hard disk in available spaces. ideally, entire files would be stored together, however, as files are moved, deleted, change size, lots of small gaps begin to appear on the disk.
  • when writing files to disk, OS splits files into smaller blocks to fill up the gaps.
  • over time the disk becomes more fragmented, making reading and writing files slower as the red/write head has to move back and forth across the disk.
  • defragmentation software recognises data on the hard drive to put fragmented files back together. it also moves all files to collect all the free space together. this prevents further fragmentation.
117
Q

why is defragmentation not used on SSDs?

A
  • as SSDs use flash storage with no moving parts, fragmentation doesn’t cause any problems - they can access data just as quickly however it’s arranged.
  • SSDs have a limited number of read/writes so defragmentation can shorten their lifespan.
118
Q

what are backup utilities?

A
  • backup utility is software with facilities such as scheduling of regular backups, creating rescue disks, disk images, and options for full or incremental backups.
119
Q

what is a backup?

A
  • a backup is a copy of a computer’s system files and settings stored externally, so data can be recovered in the event of data loss eg. fire, theft, flood, malware, hardware failures etc.
120
Q

what are the types of backups?

A
  • full: a copy is taken of every file on the system. often take a lot of storage space and can take a long time to create, but are faster to restore from. to restore from full backups, only the latest back-up is needed.
  • incremental: only files created or edited since last backup are copied. they use less storage space and are quicker to create, but a full system restore is slow as the last full backup + every incremental backup since that point must be restored.
  • business may have a backup regime where full backup is taken every week, with incremental backups every day.
121
Q

what is compression software?

A
  • reduces the size of files so they take up less disk space.
  • used a lot on the internet to make files quicker to download.
  • standard file formats include .zip or .rar.
  • compressed files need to be extracted before they can be used.
122
Q

what is encryption software?

A
  • encrypts data to stop third-parties from accessing it.

- encrypted data can be decrypted using a special key.

123
Q

what is open source software?

A
  • software where source code (programming code) is made freely available. users may legally modify source code to create own spin-off software, which can be shared under the same licence and terms as the original software eg. Mozilla Firefox, Apache HTTP server, GIMP and VLC media player. Linux-based OS developed as Android, UBUNTU and Debian.
  • users actively help improve software by suggesting bug fixes and improvements to original developers.
124
Q

pros and cons of open source software

A
  • PROS: usually free, made for greater good, not profit (benefits everyone, encourages collaboration, sharing of ideas), software can be adapted by users to fit needs, wide pool of collaborators can be more creative and innovative that the programmers of one company. popular software is very reliable and secure (any problems are quickly solved by the community).
  • CONS: small projects may not get regular updates so could be buggy or have unpatched security holes. may be limited user documentation, no warranties, no customer support (but community forums often make up for this), companies may not want competitors to see source code.
125
Q

what is proprietary software?

A
  • software where only compiled code (final file) is released and the source code kept a secret.
  • proprietary software licenses restrict the modification, copying and redistribution of the software. it’s usually paid for eg. Microsoft, Adobe.
  • businesses often use proprietary software instead of open source and tend to have better customer support options.
126
Q

pros and cons of proprietary software?

A
  • PROS: comes with warranties, documentation, and customer support. should be well-tested and reliable as the companies reputation dependent on this. fixes and updates will come regularly. usually cheaper for companies than developing own custom-built software.
  • CONS: expensive,software may not exactly fit user’s needs and they can’t do anything about it, software companies may not maintain older software after warranties expire (want people to buy latest product).
127
Q

what are the different types of issues?

A
  • ethical: what’s considered right and wrong by society.
  • legal: what’s actually right and wrong in the eyes of the law.
  • cultural: how groups of people with particular beliefs, practices or languages may be affected.
  • environmental: impact on natural world.
  • privacy: how safe your data is being stored.
  • if a company acted legally but not ethically, it would lose public trust, so many companies have a code of conduct to show they take ethical issues seriously (may invent own code or agree to follow standard one).
128
Q

what are stakeholders?

A
  • individuals or groups of people who have an interest in or are affected by a particular scenario eg. actions of a company or development of new technology.
  • may include company’s owners, employees, shop that sells company’s products, customers, company’s hardware suppliers and local community.
  • each group of stakeholders has different priorities which my conflict with those of others.
129
Q

what are privacy issues?

A
  • many websites require users to provide personal information in order to set up an account, and social media websites encourage you to post about personal life. cloud computing websites allow users to upload personal files to servers.
130
Q

what are privacy issues?

A
  • many websites require users to provide personal information in order to set up an account, and social media websites encourage you to post about personal life. cloud computing websites allow users to upload personal files to servers.
  • companies may make your personal information available to their website users or the whole internet, and may sell them to other organisations (eg. targeted adverts and spam emails) if within bounds of privacy agreement, which few people read so are unaware, and even if they do read the terms, they have no choice but to agree if they want to use the website or software.
  • users can change their privacy settings, but websites often have relaxed privacy settings by default, or the privacy settings can be hard to find and understand.
  • users have to trust companies to keep their information secure, but this doesn’t always happen (various high profile cases where customer data held by large companies have been leaked or stolen).
  • also issues around having so much personal information accessed via mobile devices, which may be stolen.
131
Q

what is internet censorship?

A
  • when someone tries to control what other people can access on the Internet.
  • eg. UK gov restricts access to pornography, gambling and other inappropriate websites to protect children.
132
Q

what is computer surveillance?

A
  • when someone monitors what other people are accessing on the internet.
  • eg. government intelligence agencies may use packet sniffers and other software to monitor internet traffic, certain key words and phrases that may alert illegal activities.
  • in some countries, Internet Service Providers (ISPs) keep a record of all websites visited by all its customers for a certain amount of time.
133
Q

for and against censorship and surveillance:

A
  • FOR: protect children and stop terrorism.

- AGAINST: cyber censorship and mass surveillance.

134
Q

what is the impact of new technology on social well-being?

A
  • companies release new technology regularly and pay for advertisements to promote it, to influence and pressure people into buying / upgrading.
  • increased peer pressure (children pressured to own latest device, parents pressured into buying them).
  • smartphones make it easier for people’s work to intrude personal life (can be contacted at any time), so stressful.
  • face-to-face social interaction neglected.
135
Q

what is cyber bullying?

A
  • when somebody uses social media to deliberately harm someone else.
  • includes trying to intimidate or insult them, or humiliate or defame them.
  • can cause serious distress -> suicide.
136
Q

what is trolling?

A
  • when someone tries to cause public arguments with others online.
  • trolls do this for their own amusement or to gain attention.
137
Q

cyber bullying, trolling, sexting etc.

A
  • cyber bullying and trolling may be a result of the anonymity that the Internet gives people.
  • Internet made it easier for children to access inappropriate material -> parents and schools can use parental-control software to stop this.
  • sexting (sending sexually explicit messages of images) is more common due to video messaging applications becoming more popular, but is dangerous as the mages can be forwarded. there are now laws to prevent this.
138
Q

what health problems are caused by technology?

A
  • eyestrain from looking at a device for too long (bad lighting, flickering screen, sunlight glare on screen -> suitable lighting, screen at distance from eyes and take regular breaks).
  • repetitive strain injury (RSI) is when body parts become damaged due to repetitive movements over a long period of time (corrected with proper posture, arranging desk properly, take regular breaks).
  • back problems due to poor posture (corrected with adjustable chair, foot rest and adjustable monitor).
139
Q

how have technology and the internet shaped our culture?

A
  • selfies really popular -> makes people more attention-seeking and self-obsessed.
  • viral (videos, images or messages that have rapidly spread over social media) -> promotional campaigns.
  • social media and blogging websites allow people to publish writing, art and other media -> voice to those ignored by mainstream media.
140
Q

how do we do business with new technology?

A
  • music and television streaming services allow customers to listen and watch media for less money using a subscription service (but some unhappy eg. musicians don’t think they get paid enough)
  • sharing economy is name given to services which use new technology to let people make money from things they already own eg. Uber and Airbnb.
  • cheap, but draw customers away from taxi firms and hotel owners and more risky eg. sharer may not know safety regulations they should follow so insurance policy won’t cover is there’s damage or theft.
141
Q

what is the digital and global divide?

A
  • the digital divide created by the fact that some people have greater access to technology than others eg. those without the Internet at a huge disadvantage.
  • the global divide is created by the fact that the level of access to technology is different in different countries. (richer countries = greater access, so increased the inequality between poorer and richer countries).
142
Q

what is being done to reduce the digital divide?

A
  • projects eg. One Laptop Per Child is charity which provides laptops to children in Africa, Central Asia and South America.
  • British community projects aimed at improving internet coverage in rural areas.
143
Q

what causes digital divide?

A
  • some don’t have enough money.
  • urban areas are likely to have greater network coverage than rural areas.
  • some don’t know how to use the internet so are shut to the opportunities they offer eg. older people as have limited experience.
144
Q

what are character sets?

A
  • collections of characters that a computer recognises from their binary representation.
  • contain alphanumeric characters and special characters which do certain commands, eg. space, enter and delete.
  • number of characters in character set = how many bits you’ll need.
145
Q

how do keyboards work?

A
  • when you press a button on your keyboard, it sends a binary signal to the computer telling it which key you pressed.
  • the computer then uses the character set to translate the binary code into a particular character.
146
Q

what is ASCII?

A
  • most commonly used character set in the English-speaking world.
  • each ASCII character is given a 7-bit binary code, meaning ti can represent a total of 128 different characters, including all letters in the English language, numbers, symbols and commands.
  • and extra bit (0) is added to the start of the binary code for each ASCII character, so each ASCII character fits nicely into 1 byte.
147
Q

what is extended ASCII?

A
  • character set which gives each character an 8-bit binary code, allowing for 256 characters to be represented. The first 128 characters are in exactly the same order as the ASCII characters.
  • useful for many European languages eg. French and German which include accents on some of the vowels.
148
Q

what is Unicode?

A
  • comes in several forms and tries to cover every possible character that may be written.
  • most common forms are 16-bit and 32-bit binary codes.
  • covers all major languages, even those that use a completely different alphabet.
149
Q

how are images stored?

A
  • bitmap images are made of pixels, and the colour for each pixel is represented by binary code.
  • number of colours available = number of bits the code has.
  • greater range of colours and shades = increase number of bits for each pixel.
  • most devices use 24-bit colour depth, with 8 bits used to indicate levels of red, green and blue needed for each pixel. it is estimated that the human eye can see 10 million different colours, so 24-bit colour depth should cover every colour that you could possibly see.
150
Q

what is colour depth?

A
  • number of bits used for each pixel.

= 2 to the power of bpp (number of bits per pixel)

151
Q

what is resolution?

A
  • density of pixels in an image, measure in dots per inch (dpi).
  • higher resolution = more pixels in certain area = better quality image.
  • increasing resolution or colour depth means there are more bits in the image, improving image quality but increasing file size.
152
Q

what is metadata?

A
  • information stored in an image file which helps the computer recreate the image on screen from the binary data in each pixel.
  • eg. image’s file format, height, width, colour depth and resolution. can also include extra information eg. time and date that the image was created or last edited.
  • without metadata, devices would not be able to display the image on screen as intended.
153
Q

how is sound stored?

A
  • sound is recorded by a microphone as an analogue signal (pieces of continually changing data), which is converted into digital data (done by analogue to digital converters).
  • the process of converting analogue to digital is called sampling: sample the amplitude of the continuous analogue sound wave at regular intervals -> digital curve is created, this is the same shape as the analogue sound wave, but it is not continuous and so has lost data.
  • the amplitude can only take certain values depending on the bit rate.
  • digital data can be improved by taking samples more regularly.
154
Q

what are sampling intervals?

A
  • gaps between each of the points where the analogue recording is sampled eg. sampled every 5 milliseconds, so the sampling interval would be 5 ms.
155
Q

what is sampling frequency/sample rate?

A
  • how many samples you take in a second.

- usually measured in kilohertz (kHz).

156
Q

what is sample size?

A
  • number of bits available for each sample.
    bit rate = sampling frequency x sample size
  • measured in kilobits per second (kbit/s)
157
Q

what happens is you increase sampling frequency?

A
  • analogue recording is sampled more often = sample sound will be better quality and will more closely match the original recording.
  • the digital file will pick up quieter sounds, even if they are happening at the same time as louder ones = sampled sound is closer quality to the original recording.
  • increasing sampling frequency and sample size increases bit rate -> increase number of bits in the sound file so larger file.
158
Q

what is data compression?

A
  • it is when we make file sizes smaller, while trying to make the compressed file as true to the original as possible.
159
Q

what are the uses for data compression?

A
  • smaller files take up less storage space on a device.
  • streaming and downloading files from the Internet is quicker as they take up less bandwidth.
  • it allows web pages to load more quickly in web browsers.
  • email services normally have restrictions on the size of the attachment you can send, so compression allows you to send the same content with a much smaller file size.
160
Q

what is lossy compression?

A
  • works by permanently removing data from the file, which limit the number of bits the file needs and so reduces it’s size.
  • eg. MP3 (audio), AAC (audio), JPEG (image).
161
Q

what is lossless compression?

A
  • makes the files smaller by temporarily removing data to store the file and restores it to its original state when it’s opened.
  • eg. FLAC (audio), TIFF (image), PNG (image).
162
Q

what are the pros of lossy compression?

A
  • greatly reduced file size, meaning more files can be stored.
  • lossy files take up less bandwidth so can be downloaded and streamed more quickly.
  • commonly used so lots of software can read lossy files.
163
Q

what are the cons of lossy compression?

A
  • loses data and the file cannot be reverted back to its original.
  • can’t be used on text or software files as these files need to retain all the information of the original.
  • worse quality that the original, but this loss in quality is normally unnoticeable.
164
Q

what are the pros of lossless compression?

A
  • no reduction in quality as the data is only temporarily removed, so should look or sound like the original.
  • can be decompressed (turned back into the original).
  • can be used on text and software files.
165
Q

what are the cons of lossless compression?

A
  • only a slight reduction in file size, so still take up quite a bit of space on your device.

computer science (2 decks)

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