Computing

• Boolean logic is true or false statements represented by binary numbers 1 and 0
• A logic gate is a device performing a boolean logic operation on one or more binary inputs.
• In an AND gate both inputs must be true
• 1 = true and 0 = false
• In an OR gate either 1 input or both inputs must be true (both inputs must be 1)
• Combining OR gates and NOT gates means that the output is always the opposite of C.
• The operating system controls all the basic functions of your computer.
• An operating system and software applications that are running all need to be loaded into memory before they can be used.
• Computer systems consist of hardware and software.
• Hardware are the physical components of your computer.
• The CPU is the brain of your computer which receives input from some device, carry’s out a calculation and then sends the output to the device
• Index is always in alphabetical order
• An index is a list of data, such as a group of files or database entries
• Logic gates


  Represent how switches are used in computers
• Logic gates


  • By combining them, we create circuits that give the ability to store a file or play a video game, all by turning on and off switches
• AND gate


  Takes two inputs and gives one output. When BOTH inputs are 1, it outputs a 1. Otherwise, it outputs a 0.
• AND gate


  • Switches in a line, where both switches need to be closed for power to reach the lightbulb
• OR gate


  Takes two inputs and gives one output. When EITHER input is 1, it outputs a 1. Otherwise, it outputs a 0.
• OR gate


  • Two separate lines with switches, where power can reach the lightbulb if either switch is closed
• NOT gate


  Has one input and one output. When the input is 1, it gives an output of 0. When the input is 0, it gives an output of 1.
• Electrical switches can either be ON or OFF, corresponding to a 1 or a 0
• An AND gate returns a 1 if both its inputs are a 1. Otherwise it returns a 0
• An OR gate returns a 1 if either its inputs are a 1. Otherwise it returns a 0
• A NOT gate flips the input, so a 1 becomes a 0 and vice versa
• Logic Diagrams


  Diagrams with inputs and outputs that represent logic circuits
• Truth Tables


  Tables that map out the range of possible results from logic circuits
• Combining logic gates to produce simple circuits

  1. Start with the brackets on the inside and work outwards

  2. Represent the circuit as a Boolean expression starting with the output Q
• Combining logic gates


  • Q = A AND (B AND C)
  • Q = NOT (A OR B)
  • Q = (A OR B) AND NOT C
• Solving problems using truth tables


  1. Build your inputs

  2. Check if any inputs are NOTed

  3. Build your expressions from the initial inputs

  4. Look at the final output
• Solving problems using truth tables

  • Q = A AND NOT B
  • Q = (A OR B) AND C
  • Q = (A AND NOT B) OR (A AND NOT C)
• Programmers use truth tables to work out complex logical IF ELSE statements
• Truth tables


  • Follow four rules
  • Step 1 - Build your inputs
  • Step 2 - Check if any inputs are NOTed
  • Step 3 - Build your expressions from the initial inputs
  • Step 4 - Look at the final output
• Main memory is usually held at a physically separate location on the motherboard from the CPU chip.
• There are 3 buses that we need to look at:

  • The Control Bus
  • The Address Bus
  • The Data Bus
• The control bus will send the instruction we are performing
• The data bus is used to send the data we are either going to put into main memory or get out of main memory
• Local area networks can be either client/server networks or peer-to-peer networks
• A client/server network involves a central server from which other PCs (clients) can connect to.
• In a peer-to-peer network, all computers have equal status as both servers and clients.
• Network topology refers to how devices on a LAN are connected together.