C. Output  Unit :

With the help of output unit computer results can be provided to the user or it can be stored in stograge device permanently for future use. Output data from main storage go to output device under the control of CPU output instructions.

Example of output devices: Printer, Monitor, Plotter, Hard Disk, Floppy Disk etc.

D. Memory Unit :

Memory unit is used to store the data and program. CPU can work with the information stored in memory unit. This memory unit is termed as primary memory or main memory module. These are basically semi conductor memories.

There ate two types of semiconductor memories -

• Volatile Memory          : RAM (Random Access Memory).
  
• Non-Volatile Memory : ROM (Read only Memory),  PROM (Programmable ROM)
                                 EPROM (Erasable PROM),  EEPROM (Electrically Erasable                                 PROM).