Computer Science

• Compiler


  A piece of software that takes source code and converts it to machine code
• Machine code


  The binary representation of an instruction, split into the opcode and the instructions data
• Assembly code


  Uses text to represent machine code instructions, or mnemonics
• Components of a processor

  • ALU - Arithmetic Logic Unit
  • CU - Control Unit
  • MU - Memory Unit
• Control Unit (CU)


  Manages the execution of machine code by sending control signals to the rest of the computer. Control signals are sent via a control bus to connected devices, such as hard drives or the graphics card.
• Clock speed


  The measure of how quickly a CPU can process instructions
• Memory Unit


  Pulls instructions and data from main memory into the registers for processing
• Arithmetic Logic Unit (ALU)


  Responsible for carrying out logical and mathematical operations e.g. division, multiplication
• Memory Unit (MU)


  Stores currently running programs, current files and the operating system. The fetch–decode–execute cycle describes the whole process of executing a single instruction.
• Control bus


  Carries signals around the CPU, generated by the CU to coordinate the fetch-decode-execute cycle
• Address bus


  Carries memory addresses from the processor to primary memory
• Data bus


  Carries data and instructions to and from the CPU and RAM in a Von Neumann processor
• Processor speed


  Measured by the number of clock cycles the processor can perform in a second, measured in hertz (Hz)
• Converting binary (base 2) to decimal (base 10)

  Steps to convert
• Hardware


  The physical parts of the computer, both internal and external
• External hardware components


  • Monitor
  • Mouse
  • Keyboard
  • Printer
• Internal hardware components


  • Processor
  • Hard disk
  • Memory chips
  • Sound cards
  • Graphics cards
  • Circuitry to connect devices
• Software


  Any program that can be run on a computer
• Assembler


  A program that translates assembly language into machine code
• Interpreter


  A program for translating a high level language by reading each statement in the source code and immediately performing the action
• Bytecode


  An intermediate code between source code and object code. Bytecode is translated into appropriate instruction code by a virtual machine.
• Scheduling


  The process of allocating access to the processor and other resources
• Memory management


  How the operating system uses RAM to optimise computer performance
• Virtual memory


  When applications need more memory than a computer has, the OS will use a section of secondary storage to mimic RAM
• File management


  The OS is responsible for managing the files stored and the folders they are stored in
• Input/output management


  The OS is responsible for dealing with input devices (keyboards, mouse) and output devices (screen, printers)
• Debugging


  The process of finding and correcting errors
• Declaring all variables and constants at the beginning of a program forces you to plan first and allows the computer to quickly identify variables it doesn't recognise
• Meaningful variable names


  Help identify and trace bugs, allow the programmer to follow the code more easily
• Definite iteration


  Iterating for a definite period
• Indefinite iteration


  Iterating until a condition is met
• Benefits of breaking a program into manageable blocks

  • Can be called at any time using the subroutine's unique name
  • Gain an overview of how the program is put together
  • Can use top-down approach to develop the whole project
  • Easier to test and debug as each subroutine is self-contained
• Subroutines are useful for group projects with other developers as they help each developer to develop small sections of the project
• Subroutine


  A self-contained block of code that can do one or more related processes
• Function


  Like a subroutine but it returns a value
• Advantages of functions


  • Can make the overall code neater and easier to understand
  • Makes the code less repetitive
• Sampling


  The process of converting analogue sound waves into a digital form
• Sound synthesis


  Sound that is produced digitally rather than in analogue format
• ADC


  Converts analogue data into digital form to get it into a computer
• DAC


  Converts digital data back into analogue form to hear it from a computer