Lessons on Functional Units of Computers

  • Input unit
  • Output unit
  • Memory
  • Arithmetic and logic unit
  • Control unit

Input units

Input units are used to feed the data to the computers.

Different Input Units:

Output Units

Output units are used to give the results of processing to the user.

Different Output Units

Memory unit

Memory units are used to process and store the data/result

Computer memory system can be broadly classified into four groups:

  • Internal Memory
  • Main Memory
  • Cache Memory
  • Secondary Memory
  • Internal memory : These are the set of CPU registers

    What are CPU registers?

    • These registers are made up of group of flip flops
    • Each flip flop will store one bit of memory
    • Stores temporary results during the computation process.
    • Cost of these registers is high.

    Main Memory is made up of Random Access Memory (RAM) and Read Only Memory (ROM)

    Features of Primary memory: Random Access Memory (RAM)

    • RAM is volatile
    • Made up of semiconductor storage cells.
    • Each cell is capable of storing one bit of information. So word is group of these cells
    • Processor can directly access the main memory
    • During execution, program must be present in main memory
    • Addresses are the numbers used to identify successive locations.
    • Using these addresses contents from the memory is retrieved or written

    Features of Main Memory: Read Only Memory (ROM)

    • ROM is not volaitle, you can read the contents already written into it and can not write anything in it
    • It contains the instructions which are used during the start up of computers
    • The set of instructions present in ROM are called as Basic Input-Output System (BIOS)

    Cache Memory

    Features of Cache Memory

    • Like RAM, Cache memory is also volatile
    • Made up of semiconductor storage cells.
    • Each cell is capable of storing one bit of information. So word is group of these cells
    • Processor can directly access this memory
    • It contains most frequently used instructions
    • Addresses are the numbers used to identify successive locations.
    • Using these addresses contents from Cache memory is retrieved or written
    • Storage capacity of Cache is samll compared to RAM but it is more faster than RAM
    Note: More information on Cache memory in Next lesson

    Secondary Memory

  • Used for permanent storage of data
  • Capacity is higher than main memory
  • Slower than main memory
  • System programs, data files etc. are stored here
  • Information from the secondary memory is accessed indirectly through the I/O programs that transfer information between main memory and the secondary memory
  • Hard disk, floppy disk, Compact Disk(CD), Digital Versatile Disk (DVD), Flash Disk, Memory Card etc. are the examples of secondary memory
  • Lessons on Basic structure of Computer << Previous
    Next>> Lesson on Cache Memory and Memory Access modes


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