Computing Revision YR8

Computational Thinking
1. A set of problem-solving methods involving understanding the problem, developing possible solutions and presenting them in a way a computer can understand
Decomposition
1. Breaking down a complex problem into smaller more manageable parts
Pattern Recognition
1. Looking for similarities/ trends in and among problems
Abstraction
1. Focussing only on important information and removing unnecessary details
Algorithm
1. Developing a step-by-step solution to the problem, or the rules to follow to solve the problem.
2. Code
  1. The implementation of an algorithm in a programming language
3. Searching Algorithm
  1. A set of instructions to conduct a search for data
4. Sorting Algorithm
  1. A set of instructions to put data in order
Binary Search
1. A method of searching which involves a data set being halved at each step
Linear Searching
1. A method of searching involving moving from one item to the next in sequence
Bubble Sort
1. A method of sorting involving repeatedly passing through a list, comparing, and swapping items in the wrong order
Micro:bit
1. A pocket sized computer that can be programmed
Programming
1. Designing and building an executable computer program
Sequencing
1. Carrying out instructions one after the other
Selection
1. A decision, or a question, that affects the output of the program
Iteration
1. The repetition of steps, often referred to as a 'loop'
Variable
1. An identifier for a storage location in memory which contains a value that can be changed (stores data in a computer program)
2. Data Types
  1. Character (single character)
  2. Real (decimal number)
  3. Integer (whole numbers)
  4. Boolean (true/false, yes/no)
  5. String (more than 1 character)
Networks
1. LANs
  1. A LAN is a network that is geographically confined to one building or site. Examples include networks employed by small businesses, small organisations, schools, colleges, universities and in homes.
  2. Connecting to a LAN: WIFI (It uses radio waves to connect computers to the LAN) and Ethernet Cables (A specification that enables computers to communicate with each other).
2. WANs
  1. A wide area network (WAN) is a network that is spread over a wide geographical area. It can cover more than one site, or be spread across a country, or even the world.
  2. Organisations that have more than one office or branch, such as banks, tend to use a WAN. The WAN allows the head office to communicate and share data with the sub-offices and branches. Communication is done through national telephone infrastructures or via wireless transmission. Each office or branch has its own LAN that is connected together using the WAN.
  3. Connecting to a WAN: Modems/ Routers, telephone connection, mobile data (GPRS) or cable/satellite
3. WPANs
  1. Wireless Personal Area Network, It allows us to pair devices over a small range. You can use bluetooth to connect to WPAN. Examples include connecting to Bluetooth speakers through a smartphone.
4. A network is two or more computers (or other electronic devices) that are connected together for the purpose of communication. They are connected by a wired medium such as cables, or by a wireless medium such as Wi-Fi.
5. Advantages:
  1. - File sharing = Users can share files with other users
  2. - Hardware sharing = Users can share hardware, such as printers
  3. - Communication = Users can communicate via email, chat, or by video
  4. - Roaming access = Users can sign in to any computer on the network and be able to access their files
  5. LARGER NETWORKS:
    1. - Centralised maintenance and updates = Network managers can apply software updates across a network, removing the need for a user to worry about having to do so
    2. - User monitoring - Network managers can monitor what users do on a network
    3. - Levels of access = Different users can be given different access rights. This gives network managers the ability to generally restrict user access to certain files, while granting permission to specific users
6. Disadvantages:
  1. - Cost = Additional equipment is needed to allow computers to communicate
  2. - Management = Networks require management by technical staff such as network manager
  3. - Spread of malware = Viruses and other forms of malware can easily spread across an improperly secured network
  4. - Hacking = Once a device is connected to another device, it is possible that data may be accessed without the device owner's permission
7. NETWORK HARDWARE COMPONENTS
  1. Network Interface Card (NIC)
    1. A printed circuit board or card that is installed in a computer so that it can be connected to a LAN
  2. Router
    1. A device for connecting devices together to form a network. It connects all devices to the modem by giving them an internal IP adress.
    2. Routers are one of the most commonly used connection devices. They are used to send data signals across the internet. Routers work by collecting knowledge of available routes to transmit data. They then determine the most suitable route for sending data. Routers are also commonly used in homes. These types of router usually contain a hub and a WAP, enabling a small peer-to-peer network to be formed. Additionally, they contain a modem, which allows users to connect to the internet.
  3. Modem
    1. Stands for modulator/ demodulator. Sends/receives data between computers over telephone circuits, It converts the digital signals from the computer into audio tones for transmission over ordinary telephone lines and converts incoming audio signals into digital signals for the computer. Normally, they are built into free routers given out by Internet Service Providers (ISP)
  4. Hub
    1. A hub is a small device that allows wired devices to connect to a network. Hubs have no knowledge of the devices connected. Any signal (traffic) that arrives at the hub is transmitted to all connected computers. This affects network performance as many unnecessary signals are transmitted across its connections
  5. Wireless Adapter
    1. A printed circuit board with a built in transmitter/receiver for sending signals so that it can be connected to a LAN
  6. Switches
    1. Switches are similar to hubs, with one important difference - a switch records which computers are connected to which ports. When traffic is received, the switch forwards the traffic to its intended recipient only. This improves network performance by cutting down on unnecessary transmissions.
8. Security Measures:
  1. - Firewalls: It controls which program/ software may send/receive data packets from computer/networks. It also stops unauthorised/untrusted users from accessing your computer system and only authorised/trusted programs are allowed to send/receive data packets. Useful for keeping whatever comes from the internet and into our computer system secure; also makes sure that any dangerous malware doesn’t intrude over our activity.
  2. - Anti-Malware Software - It scans your computer system regularly to check if there’s any malware installed - then it moves it to the side (quarantines it) and doesn’t delete it - instead it asks permission from the user to delete it from your computer system. To be safe, you need to install an anti-malware software to scan the downloads and attachments that you receive. It also needs to be updated regularly to keep up with the latest threats. Thus, malware deletes, corrupts or cleans.
  3. - Encryption - It encrypts (scrambles) data packets using a cipher so that unauthorised users can not read it. A key is needed to decrypt (unscramble) the data packets in order to be read. The recipients (websites) need to have a ‘’https://’’ at the start of the URL to make sure that data packets are encrypted. Also WiFi connection should be encrypted to stop users accessing your network
  4. - Passwords - Passwords are basically a barrier between unauthorised users accessing your data and then your actual data. That barrier is you making a good password. A good password includes lower and upper case letters (alphanumeric). It may also include numbers and symbols ( , . / ; @).
9. Network Threats
  1. Phishing
    1. A cybercrime in which a target/s are contacted by email, telephone or text message by someone posing as a legitimate institution to lure individuals into providing sensitive data such as personally identifiable information, banking and credit card details and passwords
  2. Hackers
    1. Unauthorised access to our private information without accord anonymously
  3. Trojan Horses
    1. Pretending to be a trusted website/app when in reality, it's a type of malware causing harm to a computer system
  4. Zombies
    1. It's a computer connected to a network that has been compromised by a hacker, a virus or a Trojan. It can be used remotely for malicious
  5. Viruses
    1. It's a type of computer program that when executed, replicated itself by modifying other computer programs infecting them. (they need a host program)
  6. Spyware
    1. It is a malicious software which installed in a users OS, it can spy and record phone calls, have access to messages, photos and personal information like important documents etc.
  7. Adware
    1. It's a malicious software that automatically displays or downloads advertising material such as banners or pop-ups when a user is online and when clicked, it steals personal data
10. Connection Types + Adv & Disadv
  1. - WiFi: Advantages: Good for connecting to portable devices like smartphones etc. Disadvantages: Slower data transfer that Ethernet, can be hacked and has a small range
  2. - Ethernet: Advantages: Faster data transfer than WiFi (100 meter range) Disadvantages: The cables can be more expensive than a WiFi connection
  3. - Bluetooth: Advantages: 7 devices can be connected at once. Disadvantages: range is short and can be hacked
  4. - GPRS: Advantages: Good for mobile devices and can be used on the move. Disadvantages: It's expensive (requires SIM card), connection is slower in some areas
Computer Hardware
1. CPU
  1. The purpose of a CPU is to process data using the Fetch, Decode, Execute cycle. - It's the cycle that the CPU follows from boot-up until the computer is shut down in order to process instructions. It firstly fetches data packets from the RAM, the the CPU itself makes sense of it and tries to 'decode' it and then gets executed (sent away to the output devices e.g.monitor)
  2. Clock Speed
    1. The clock speed measures the number of fetch, decode, execute cycles in the CPU executed per second. Measured in GHz
    2. The higher the clock speed, the more instructions can be executed per second so the performance of the computer will be improved and programs and data will load faster.
  3. Cores
    1. Cores are small CPUs or processors built into a big CPU or CPU socket. It can independently perform or process all computational tasks simultaneously.
    2. If there are more cores, more programs will be opened at the same time which will mean t hat the CPU will execute more instructions every second so the computer's performance will be improved
    3. Dual core means 2 independent processors. Quad core means 4 independent preocessors
  4. Cache
    1. Cache is a storage hardware that allows to help websites, browsers and apps load faster. A cache makes it easy to quickly retrieve data, which in turn helps devices run faster
    2. Cache memory stores frequently-used instructions. Cache memory is faster and more expensive than RAM. If there is a larger amount of cache memory storage, a greater number of frequently-used instructions can be stored. This means that programs will load faster which also means that more instructions can be accessed quickly, which will improve the performance of the computer
2. RAM
  1. It's purpose is to store the programs/apps/ parts of the OS and data files we are currently using. It is volatile, meaning that the data is not stored when t he computer system is switched off.
  2. Virtual Memory
    1. Virtual memory is used when there is insufficient RAM to open the programs and files. Virtual memory is stored on the secondary storage
    2. If you upgrade it to more RAM, this means that you don’t have to use virtual memory as much. This is an advantage because RAM is also faster at accessing data than virtual memory. Disadvantage: virtual memory is slower to access data compared to RAM. This will make loading programs slower compared to using RAM
  3. The greater the amount of RAM, the more instructions and data can be stored and processed while a program is running which will also mean that more programs can be opened at the same time. This means that less instructions will be stored in the much slower virtual memory and will therefore improve the performance of the computer and you won't need to rely on virtual memory as much.
3. Secondary Storage
  1. Optical Storage
    1. Is any storage method in which data is written and read with a laser. CDs, DVDs and Blu-Ray are examples of this type of storage.
      1. Advantages: Cost effective and very portable
        Disadvantages: Not very durable and has a limited capacity
  2. Magnetic Storage
    1. Data is stored by magnetising the surface of flat, circular plates called platters. These platters rotate at a very high speed.
      1. Advantages: Cost effective due to having a larger capacity than solid state.
        Disadvantages: Not as durable due to moving parts and reads/writes data slower in comparison to solid state.
  3. Solid State Storage
    1. Uses microchips to store data instead of magnetised disks and do not contain any moving parts.
      1. Advantages: More durable and can read and write data much faster than magnetic storage. It is also more energy efficient.
        Disadvantages: Less cost effective in comparison to magnetic because it has a much smaller capacity. It also has a limited read/write lifespan.
4. Embedded Systems
  1. Embedded systems are computers built into other devices. They are often used as control systems - they monitor and control machinery. They are dedicated systems which means that they are designed for a single task. A they are dedicated to a single task, they are much easier to design, cheaper to produce and more efficient at doing their task.
  2. Washing Machine:
    1. The embedded system in a washing machine will:
      1. - Control the water pumps so that they do not overflow
        - Control the water release mechanisms
        - Control the washing powder tray release
        - Lock the washing machine door until washing cycle has finished
        - Control the temperature for the different wash cycles
Increment
1. When a variable increases in value (e.g. score increments by 100)
Decrement
1. When a score decreases in value (e.g. libes decrements by 1)
Flowchart
1. An algorithm which is a visual representation of the steps needed to solve a problem
2. - Input/Output = This shows something that is going in our out the system
3. - Terminator= This either contains START or END
4. - Process= This shows something that is happening
5. - Decision = We use these when we need to make a choice. Decisions must have two exits. YES and NO
6. - Connector= Shows the direction of data through the flowchart
Pseudocode
1. An algorithm which uses text to show the steps needed to solve a problem
Data Representation
1. Bit
  1. A single 1 or 0
2. Nibble
  1. 4 bits
3. Byte
  1. 8 bits
4. Kilobyte
  1. 1024 bytes
5. Megabyte
  1. 1024 Kilobytes
6. Gigabyte
  1. 1024 Megabytes
7. Terabyte
  1. 1024 Gigabytes
8. Binary
  1. A number system that contains two symbols, 0 and 1. Also known as base 2. All information that is processed by a computer is in the form of a sequence of 1s and 0s. Therefore, all data that we want a computer to process needs to be converted unto binary
    1. Base 2
      1. The binary counting system uses 2 symbols - 0 and 1
9. Denary/Decimal
  1. The number system most commonly used by people. It contains 10 unique digits 0 to 9. Also known as decimal or base 10
    1. Base 10
      1. The denary counting system uses 10 symbols - 0 to 9
10. ASCII
  1. A 7-bit character set used for representing English keyboard characters
11. UNICODE
  1. A 16-bit character set. Is capable of representing 65,536 different and a much wider range of characters
12. Binary Addition
  1. Binary Addition Rules
    1. 0+0=0
    2. 1+0=1
    3. 1+1 = 0 (carry the 1)
    4. 1+1+1 = 1 (carry the 1)
  2. Binary addition is a simple mathematical operation used to add two binary numbers together. It involves adding two or more binary numbers together.
  3. Overflow error
    1. Sometimes, when adding up two binary numbers we can end up with an extra digit that doesn't fit. This is called an overflow error.
    2. An overflow error occurs when the largest number that a CPU register can hold is exceeded
13. Images
  1. Pixel
    1. A single point in an image
  2. Resolution
    1. The number of pixels that make up an image e.g. 800x600
  3. Colour Depth
    1. The number of bits used to store each pixel is called the colour depth. Images with more colours need more pixels to store each available colour. This means that images that use lots of colours are stored in larger files. E.g. 8 bit colour and 24 bit 'True Colour'
  4. Image Quality
    1. Image quality is affected by the resolution of the image. The resolution of an image is a way of describing how tightly packed pixels are. In a low-resolution image, the pixels are larger so fewer are needed to fill the space. This results in images that look blocky or pixelated. An image with a high resolution has more pixels, so it looks a lot better when you zoom in or stretch it. The downside of having more pixels is that the file size will be bigger, taking more storage space.
  5. Images also need to be converted into binary in order for a computer to process them so that they can be seen on our screen.. Digital images are made up of pixels. Each pixel in an image is made up of binary numbers. If we say that 1 is black (or on) and 0 is white (or off), then a simple black and white picture can be created using binary. To create the picture, a grid can be set out and the squares coloured (1 - black and = - white). But before the grid can be created, the size needs to be known. This data is called metadata and computers need metadata to know the size of an image. If the metadata for the image to be created is 10x10, this means the picture will be 10 pixels across and 10 pixels down
  6. 00 - white
  7. 01 - blue
  8. 10 - green
  9. 11 - red
  10. 1 bit per pixel (0 or 1):two possible colours
  11. 2 bits per pixel (00 or 11): four possible colours
  12. 3 bits per pixel (000 or 111): eight possible colours
  13. 4 bits per pixel (0000 or 1111): 16 possible colours
  14. DPI
    1. Dots per inch; number of individual dots that can be placed in a line within the span of an inch

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	Created by Darius C almost 3 years ago