Hardware notes

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  • hardware is the term that describes the physical components of a computer system, anything that can be seen or touched
  • this includes the input, output and storage devices


  • carries out the processing of a computer system
  • the core of every computer system
  • has two parts: control unit and arithmetic and logic unit (ALU)
  • control unit uses electrical signals to direct the system to execute the instructions in stored programs
  • ALU carries out all of the arithmetic and logical operations including addition, subtraction and comparisons
  • needs access to RAM (random access memory) where programs are stored and cache memory where data waiting to be processed is stored.
  • RAM and cache memory are called primary storage and are part of the computer's processing capabilities
  • hard drives and other devices are called secondary storage and these hold data to be kept when the computer is turned off
  • cache memory is fast memory that is located very close to the main CPU with dedicated connections so the CPU has fast access to frequently used data
  • cache memory is relatively expensive compared with RAM
  • CPU runs an endless fetch-decode-execute cycle
  • after the computer is switche don, the CPU will look in the read-only memory (ROM) for the first program to load and execute
  • this is the boot sequence
  • the speed of this fetch-execute cycle is determined by an electronic clock chip
  • this chip uses a vibrating crystal that maintains a constant rate and the speed is measured i  hertz per second. the computer synchronises all processes to this clock signal
  • main memory is slower than the CPU
  • to overcome this, when the first instruction is requested by the CPU, the remaining instructions are automatically copied into the cache memory
  • to improve performance the control unit will look first in the cache for the next instruction to see if it has already been copied
  • the more cache memory there is, the more likely the required data has already been requested and copied to the cache memory
  • the clock speed and cache memory on a computer can affect the speed or performance of the system
  • a higher speed processor and more cache usually means better performance
  • this is limited by the speed data and control signals can move around the system
  • data and control signals move around the system on buses
  • a bus is a circuit that connects one part of the motherboard to another
  • the speed of the bus refers to how much data can move across the bus at the same time
  • you can have more than one CPU whcih makes the computer much quicker



  • the main memory in the computer
  • required for the operating system, applications that are loaded and any data currently in use
  • the more RAM available to the computer, the more programs and data it can load at the same time meaning better performance
  • is volatile and the data it stores is lost when the power to the computer is turned off
  • dynamic RAM has one transistor and a capacitor…


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