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Input and Output Devices | O Level Computer Science 2210 & IGCSE Computer Science 0478 | Detailed Free Notes To Score An A Star (A*)

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  • The role of the CPU
    • Central Processing Unit is the brain of the computer
    • Some devices have it in the form of a microprocessor
    • Sometimes, microprocessor has sensors and actuators installed as well, which makes it an embedded system to perform certain tasks.
    • Computer processes instructions using the fetch-decode-execute-cycle
    • Von Neumann computer architecture
  • Fetch Stage
    • Data is given to the computer through input devices
    • Instructions and data are initially stored in the RAM (random access memory)
    • Even a file opened from the hard drive has to first go through the RAM.
    • For data to be processed, it must be taken from the RAM to the CPU
    • Program Counter (PC) stores the address
      • Address means the location on the RAM from where a data has be read or the data has to be written
      • Program counter is a type of register
    • The address stored in PC is the address of the next instruction that needs to be processed
    • Address refers to a location on the RAM
    • Then address is then sent to Memory Address Register (MAR), and this transportation occurs in the address bus.
    • MAR knows now where it needs to find the instructions on the RAM
    • MAR sends the address to the RAM location
      • Address bus used again.
    • Data that is stored in this location is sent to the component within the CPU called MDR (Memory data register)
      • Also a register
      • Data bus is used for this purpose
    • When MDR received the instructions it send it to CIR (Current Instruction Register)
    • MDR uses the data bus to send the instruction to the CIR
    • Register is part of a component within the CPU called the Control Unit (CU)
    • Here, the decode stage will occur
  • Decode stage
    • CU decodes the instructions
    • Without decoding, instructions can not be executed
    • Instruction set is used
    • Commands that are understood and processed by CPU
    • These are in machine code
    • Once decoded, execution stage occurs
  • Execute Stage
    • The action required by the instruction is performed
    • Mathematical and logical calculations occur
    • Such calculations are performed in the arithmetic and logic unit (ALU)
    • Interim values may be generated in this process, which are in the accumulator (ACC)
      • A special register within the ALU
    • Actions for the instructions can be performed
    • The CPU acts as a conductor which tells all different components what to do.
    • These signals are sent through the control bus
  • Factors Affecting Performance of a CPU
    • 3 main factors
      • Cores, Clock speed and Cache
      • Single core contains all the CPU components required in the fetch-decode-execute cycle
      • One core means one cycle at a time.
      • Two cores means two cycles at a time.
      • Multitasking becomes possible
    • Internal Clock
      • Speed at which instructions are processed
      • Measured in hertz
      • One instruction per second is 1 hertz
    • Cache
      • Data storage within the CPU, instructions and data that the computer uses most can be stored in the cache
      • CPU doesn’t need to fetch this data from the RAM, instead directly from the cache
      • Process is quicker
      • Larger cache allows less time of accessing from the RAM
  • Input and Output Devices
    • Input device is one that allows data to be entered into a computer
    • Output device  allows results of data processing to be shown, heard, seen etc.
  • Sensor
    • It is a type of input device used in automated systems
    • Automated systems require minimal or no human interaction
    • They capture some form of data for the computer from their environment
    • This data is in analogue form
    • It could be set to any time based on when the sample needs to be taken
    • Acoustic sensor
      • Senses sound levels
    • Accelerometer
      • Measures acceleration
    • Flow
      • Measures the liquid, gas or steam that is flowing through an environment
    • Gas
      • Measures the presence and concentration of a gas within the immediate atmosphere
    • Humidity
      • Measures the level of moisture in the immediate atmosphere
    • Infra-red
      • Measures infra-red radiations
    • Level
      • Measures substance level
    • Light
      • Measures light intensity
    • Magnetic field
      • Measures the presence of a magnetic field
    • Moisture
      • Measures the amount of water
    • pH
      • Measures the acidity level
    • Pressure
      • Measures the force of pressure
    • Proximity
      • Measures closeness of objects
    • Temperature
      • Measures the temperature of an object or substance
Hunain Zia

Hunain Zia has previously achieved considerable success in the high-school educational stream, gaining a massive 154 Total A Grades and 7 Major Distinctions, a process in which he broke/ set 11 different world records, including the most A grades ever achieved, most subjects ever appeared in, most distinctions, gaining distinctions across two separate boards (Pearson Edexcel and CAIE) within the same year/ ever, and even 19 hours of constant examination. All records stand intact today. Hunain pursued his Honors Accounting Degree from the prestigious Bentley University, and then completed an LLB (in Honors) from University of London. Currently, he manages multiple social and commercial projects, has founded digital streams and works tirelessly in the education sector.

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