Memory is the main component of a computer system. It stores instructions and data in binary form that is used by the central processing unit. Memories are divided into 2 types such as.
1)    Primary memory
2)    Secondary memory

1) Primary memory: It is directly accessible by the CPU. The primary memory is of two types such as.
a)    ROM memory
b)    Read /Write memory

a) Read Only Memory (ROM) – this is a non-volatile memory and the data can only be read from this type of memory. Again ROMs are three types.

PROM (Programmable Read only Memory): it uses fusible links that can be burned by using special PROM burning circuit. It can be programmed by the user using a PROM programmer.

EPROM (Erasable Programmable Read only Memory): the information stored in an EPROM can be erased by exposing the memory to ultraviolet light.

EEPROM (Electrically Erasable Programmable Read only Memory): it is also same as EPROM but the erasing is done by electrical signals.

b)    Read /Write memory – It is a memory area where information can be written into or read whenever required by the CPU. It is required during calculation. It is also called Random access memory (RAM). RAM is of two types such as

SRAM (Static RAM): It uses flip flops for storage elements. In SRAM once data is written into memory location, the data stays unchanged unless some new data is entered into that location.

DRAM (Dynamic RAM): It uses capacitors as storage element. The dynamic RAM contents may change with time due to leakage of charge. So it is required to refresh the storage elements periodically. It consumes less power compare to SRAM.

2)    Secondary memory: The maximum capacity of primary memory is limited. So to handle more data than allowed by primary memory, secondary memory is used. And it is non-volatile i.e. data is not lost due to current failure. Magnetic tape, Floppy disk and Hard disk are some examples of secondary memory.

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