summary

• Von Neumann Architecture


  The stored program concept where instructions are moving between memory and the CPU
• Components of the CPU

  • Control Unit
  • Arithmetic and Logic Unit
  • Cache
  • Registers
• Control Unit


  Oversees the FDE as well as other components of the CPU
• Arithmetic and Logic Unit


  Responsible for the calculations performed by the CPU
• Cache


  High speed small storage memory used for storing frequently used instructions
• Registers


  • Program Counter
  • Memory Address Register
  • Memory Data Register
  • Accumulator
• Program Counter


  Holds the memory address of the next instruction to be carried out
• Memory Address Register


  Stores the memory addresses of instructions being searched for
• Memory Data Register


  Holds the data/instructions that are to be read/written to memory
• Accumulator


  Holds the result of any calculations performed by the ALU
• Fetch-Decode-Execute (Repeat) Cycle


  1. Fetch - Instruction is fetched from the Memory Address which the Program Counter is currently holding, one this is passed over the Program Counter increases by 1

  2. Decode - The Memory Address provides the location of the Memory Data to be used which is decoded by the Control Unit

  3. Execute - The instruction is carried out and the result stored in the accumulator with any Memory Data Register being updated as needed
• Embedded Systems


  A device with a specific purpose that is built into a larger device. These systems are built for reliability and generally use Read-Only Memory to avoid their purpose being changed
• Embedded Systems


  • Dishwasher
  • Washing Machine
  • MP3 Player
• Clock Speed


  Increases performance by performing more instructions per second - measured in Hertz. Higher values are always preferable
• Cache Size


  High speed small storage memory that holds frequently used instructions which make routine processes faster. However, too much Cache memory is bad as you only want a small set of frequent instructions else it takes too long to search
• Number of Cores


  The more cores in theory means the more instructions carried out but not every program is optimised for this and it isn't a direct doubling of speed from 2 to 4 cores
• Core


  A processing unit found within the Central Processing Unit
• Binary


  Conversion to and from denary values, this will be 8 bit values but do double check the question
• Hexadecimal


  • Conversion to and from binary/denary
  • 0-9 are the same
  • 10-15 are A to F
  • Hexadecimal is used as it is a shorter method of displaying data that is easier to remember, it still needs to be converted back to binary
• Binary Addition


  1. Adding two values together

  2. Overflow is always the problem, caused by having too many digits for the bits available
• Binary Shifts


  1. The act of increasing or decreasing a value by shifting

  2. Left shift increases the value

  3. Right shift decreases the value
• Characters


  • ASCII is 7 bit, Extended ASCII is 8 bit
  • Each character will take up potentially 7 or 8 bits (1 byte) per – spaces etc. are included in these calculations
  • Unicode is another character set available
  • Character set is a term that refers to all the characters a computer can use, each represented by different binary values
• Images


  • These are made up of pixels, each pixel has a binary value attached to it
  • Resolution is the term for the width x height of a screen / image
  • For calculations you will need to times the total amount of pixels by the bit depth
  • 8 colours can be represented by 3 bits
  • More bits available = higher quality, bigger file
• Sound


  • Sampling is taking a measure of the height/amplitude of a wave at a set interval
  • More samples = higher quality, bigger file
• Lossy Compression


  • This can be done by removing pixels (condensing the size of the image) or removing the amount of colours available
  • Lossy results in permanent reductions in file size and it cannot be put back to the original size once it has been compressed
  • Used on Sound/Images to make them faster to send/quicker to download online
• Lossy Compression Example


  • RRRRGGRRBBBBB becomes RRRGRBBB
• Lossless Compression


  • This is a process of marking up data in a format that means it can be unpacked back into the original size later
  • Generally used on software applications
• Lossless Compression Example


  • RRRRGGRRBBBBB becomes 4R2G2R5B
• Local Area Network (LAN)

  Covers a small geographic area using their own equipment
• Wide Area Network (WAN)


  Covers multiple sites that uses third party connections (e.g. the internet) to connect to each other
• Factors that impact network performance

  • Bandwidth (Maximum amount of data that can be transmitted at once)
  • Number of devices connected
  • Distance from Router if Wireless
  • Obstacles such as walls if Wireless
• Client-Server


  Clients request services from the servers, Servers provide them to the clients
• Hardware required


  • Router – Records IP addresses, allows internet access and records destinations
  • Switch – Uses MAC addresses, forwards information as needed
  • WAP – Wireless Access Point, as it says!
  • NIC – Network Interface Card
• Transmission Mediums


  Connecting method used, e.g. fibre optic cabling
• Domain Name Servers (DNS)

  1. Check database for IP address when requested URL

  2. If found, return IP address to client

  3. If not found, ask other DNS until found or return not found
• Star Topology


  • Switch in the middle, Easy to add new devices, Single Point of Failure
• Mesh Topology


  • Self-healing network, Lots of cabling/redundant connections
• Full Mesh Topology


  • All devices connected to each other
• Partial Mesh Topology


  • Most devices connected to each other
• Wired vs Wireless


  Wired is faster and more secure but less portable than wireless, Wireless is able to get around physical barriers and has many frequencies to allow people to connect to