Digital Technology

Chapter 5 Computer Hardware
1. Central Processing Unit
  1. Control Unit
    1. Manages the execution of instructions, usually in some sort of order, using the fetch execute cycle
    2. Has 3 main jobs:
      1. 1. Decide which instructions to carry out next and fetch it from the memory.
        2. Decode the instruction.
        3. Execute the instruction.
  2. Arithmetic Logic Unit (ALU
    1. Processes data which requires arithmetic calculations to be solved.
    2. Also performs logical comparisons, e.g. AND, OR...
  3. Immediate Access Store (IAS)
    1. Stores all programs and data temporarily while they are in use.
  4. Registers
    1. Program Counter (PC) - A register that stores the address of the next instruction to be fetched. Every time an instruction is fetched, the program counter is incremented by 1.
    2. Memory Address Register - The address of the current instruction or data being executed is temporarily stored here.
    3. Memory Data Register (MDR) - Temporarily stores data being fetched from or written to the main memory.
    4. Instruction Register (IR) - Temporarily stores the current instruction to be decoded and then executed.
    5. Accumulator - A register contained in the ALU, results of calculations are initially stored here before being transferred and stored in the main memory.
  5. Cache Memory
    1. Can be used to store temporarily frequently used instructions and data. Situated between the RAM and CPU.
2. Computer Hardware Devices
  1. Microphone - Used to transfer sound or a human voice into a computer, also used to record music in analogue and store it in digital.
    1. Advantages - STT is faster than typing, hands free.
    2. Disadvantages - Recognition rate of SST can be slow if there is background noise, sound files are bigger than text.
  2. Mouse - When moved controls the 'pointer' on a VDU (Visual Display Unit), detects movement and sends those signals back to the computer.
    1. Advantages - Requires little training, quicker to select menus and icons compared to a keyboard
    2. Disadvantages - Not as fast as hotkeys, needs a flat surface.
  3. Touchscreen - Avoids the need for a mouse, touching the sensitive screen is the same as left-clicking. Touching the screen causes a change in voltage which is used to determine the point of contact
    1. Advantages - Little ICT competence needed, Selecting and entering faster than keyboard
    2. Disadvantages - Limited number of options on screen, screens can dirty quickly.
  4. Speaker - To output sound
    1. Advantages - Useful for visually impaired, natural way to communicate.
    2. Disadvantages - Speakers require desk space, can distract others in the same working environment.
  5. Laser Printers - Produce high quality text and graphics
    1. Advantages - Faster to bulk-print, high quality.
    2. Disadvantages - Colour laser printers are expensive, because they are non-impact printers, multipart stationery cannot be used.
  6. 3D Printer - Gradually prints 3D objects one layer at a time.
    1. Disadvantages - Not economical for large scale manufacturing, limited form of printing
    2. Advantages - Fast, cheap production due to time taken, can print onto a variety of surfaces
  7. Hard Disc Drive - Consists of a number of rigid discs stacked on a spindle in a sealed unit
    1. Advantages - Costs per Gb is cheaper than external drives, greater storage than SSD's
    2. Disadvantages - Prone to breaking down, slower than 'flash' memory.
  8. Extra Devices
    1. SSD's - No moving parts, non-volatile flash memory.
    2. Memory Cards - Electronic flash memory.
    3. Smart Cards - Bank cards use 'Chip and PIN', reliable, hotel door entry systems.
3. Internal Memory
  1. Random Access Memory (RAM) - Volatile, used to hold programs and data which are currently being used: parts of the OS, applications software and documents being edited.
  2. Read-Only Memory (ROM) - Can only be read from, not written to. Non-volatile, stores boot software.
  3. Cache Memory
Chapter 6 Network Topologies
1. Types of Networks
  1. Local Area Network (LAN) - Spread over a small geographical area, like a building or office.
  2. Wide Area Network (WAN) - Spread over a large geographical area, on a global scale and requires a telecommunications link. E.g. the Internet.
2. Pros and Cons
  1. Advantages
    1. Users can save work on file servers and retrieve it from other computers on the network.
    2. Expensive hardware devices can be shared by all computers on the network
    3. Files stored on the file server can be shared through the network.
    4. Files can be backed up from all computers to the file server, much more effective than individual backups.
    5. Security on the network can be managed centrally by controlling access to data and software amongst users.
  2. Disadvantages
    1. Viruses can spread through the network easily.
    2. If there is a limit on bandwidth, when multiple users are present the network can slow down
    3. Set-up costs can be expensive as additional hardware is required (file servers, NIC, switches and routers).
    4. Additional staff are required to keep up maintenance on the network.
3. WWW, Internet and Intranet
  1. Internet - Example of a WAN
  2. WWW - An application which uses the Internet
  3. Intranet - A private network set up as a secure website, owned and managed by an organisation, only authorised users with a username and password can access it
  4. 'Internet of Things' refers to the future impact that the internet will have on our lives, the scope of the IoT will increase as technology gradually becomes less expensive.
4. Acronyms
  1. WWW - World Wide Web
  2. URL - Uniform Resource Locator
  3. HTML - Hypertext Markup Language
  4. Http - Hypertext Transfer Protocol
  5. IoT - internet of Things
  6. Wi-Fi -Wireless Fidelity
  7. NIC - Network Interface Card
5. Network Communications Technology
  1. Wi-Fi - Wi-Fi connections are made possible through radio waves and a wireless router, so there is no need for cables
    1. Advantages - Networks can be set up without the need for cabling.
    2. Disadvantages - The broadband speed and signal strength begin to weaken the farther the device is from the wireless router
  2. Bluetooth - Uses short range radio waves to connect two devices together and allow them to share data. The devices communicate directly with each other so there is no need for a router.
  3. Optical Fibre - Technology that uses very thin strands of glass to send lots of data at high speeds. Cannot be interfered with by hackers. Requires 'repeaters' for data to travel over large distaces.
  4. Mobile Communications Network - 4G mobile-phone technology is capable of high-speed internet access on a global scale. Due to its cost, its coverage is mostly focused on areas with high population.
6. Network Resources
  1. NIC - An electronic circuit board that needs to be installed into a computer to enable it to be connected to a network.
  2. Network Cables - Generally connects computers to switch or other computers, generally made from copper.
  3. Switch - Checks where data is being sent from and where it is going, is a single connection point to connect to many computers.
  4. Router - Connects a number of networks together, whether wireless or wired, IP addresses are used to determine the route the data takes.
7. Network Topologies
  1. Bus Network - All computers are connected to the 'backbone' cable, computers are easily added, if the backbone fails, the whole network goes down.
  2. Star Network - All computers connected directly to the file server, if a single cable fails, the network should still work.
  3. Ring Network - No central computer. Each computer is connected directly to 2 other devices, if a cable fails, the whole network is affected. It is difficult to add more devices.

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