comp sci paper 1

• Basic computer system model


  Input, Processing, Output and optional storage

  
• CPU


  Central Processing Unit
• Input device


  A device used to enter information into a computer.
• Output device


  any device that presents data from the computer
• Storage device


  a piece of computer equipment on which information can be stored.
• Central Processing Unit


  the part of a computer that decodes and executes instructions and manages the rest of the hardware.
• Von Neumann Architecture


  Instructions are fetched, decoded and executed one at a time.

  Instructions and data are held together in the same memory space.
• Bus


  The paths, or lines, on the motherboard on which data, instructions, and electrical power move from component to component.
• Address Bus


  carries addresses from the processor to memory and input/output devices.
• Data Bus


  sends data between the processor, memory and input/output devices.
• Control Bus


  carries signals to coordinate all the computer activities.
• CU


  Control Unit. Coordinates all the activities taking place inside the CPU.
• Control Unit functions


  1. controls the execution of instructions in the correct sequence.

  2. decodes the instructions.

  3. regulates and controls processor timing using regular pulses from the system clock.

  4. sends and receives control signals to and from other devices within the computer.
• ALU


  Arithmetic Logic Unit. Carries out all mathematical and logical operations.
• Arithmetic Logic Unit functions

  1. Logical Operations: AND, OR and NOT.

  2. Shift Operations: The bits in a binary number can be shifted to the left or the right a number of times.

  3. Arithmetic Operations: addition, subtraction, multiplication and division.
• Special Purpose registers


  special very fast memory locations within the CPU with specific purposes in the process of executing instructions.
• MAR


  Memory Address Register
• MDR


  Memory Data Register
• PC


  Program Counter
• ACC


  Accumulator
• Memory Data Register (MDR)


  Holds the data fetched from or to be written to memory.
• Memory Address Register (MAR)


  Holds the address of data ready for use by the MDR, or the address of an instruction passed from the PC.
• Program Counter (PC)


  The register that contains the address of the next instruction to be executed
• Accumulator (ACC)


  Holds the result of calculations.
• FDE Cycle


  Fetch Decode Execute Cycle. The CPU uses the FDE cycle to carry out the program instructions.
• Fetch


  1. The address A of the next instruction to be executed is copied from the PC to the MAR

  2. The PC is incremented so it points at the next instruction to be fetched. Simultaneously, the instruction held in location A is then copied into the MDR.

  3. The contents of the MDR are copied to the CIR.
• Decode


  The CU decodes the instruction in the CIR to see what is to be done next.
• Execute


  The instruction is executed.
• Cache


  Memory in the processor providing fast access to frequently used instructions and data.
• Factors affecting the speed of the CPU

  1. Clock Speed

  2. Number of Cores

  3. Cache Size
• Embedded System


  A computer system within a larger mechanical

  or electrical system designed for a

  specialist purpose.
• Some examples of where computer systems are used in the modern world

  Communications, Employment, Shopping, Manufacturing
• Examples of recent developments in computer systems

  Driverless cars, AI, robotics
• Examples of environmental impact of computer systems

  Carbon footprint, e-waste
• Examples of safety with computer systems

  robotics for bomb disposal, sensors for poisonous gasses, sensors for measuring real world data such as weather patters, seismic activity
• Stakeholders


  any persons or groups who will be affected by an action
• Examples of ethics and cultural issues with computer systems

  cyber bullying, cyber crime, use of computers in healthcare, social media use
• The Data Protection Act 1998


  The UK law that tells organisations how they must protect the personal data of real people.
• Data Protection Act 1998 - principles

  Data must be processed fairly and lawfully

  Data must be adequate, relevant and not excessive

  Data must be accurate and up to date

  Data must not be retained for longer than necessary

  Data can only be used for the purpose for which it was collected

  Data must be kept secure

  Data must be handled in accordance with people's rights

  Data must not be transferred outside the EU without adequate protection
• The Freedom of Information Act 2000

  Law that gives a general right of access to recorded information held by more than 100,000 public bodies in England, Wales and N. Ireland