• 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