Memory unit ??

Memory unit

Memory Organization

A memory unit is the collection of storage units or devices together. The memory unit stores the binary information in the form of bits. Generally, memory/storage is classified into 2 categories:

1 Volatile Memory: This loses its data, when power is switched off., Internal memory , private memory , short time storage

2 Non-Volatile Memory: This is a permanent storage and does not lose any data when power is switched off.

External memory, secondary memory, long time save

Main Memory
The memory unit that communicates directly within the CPU, Auxillary memory and Cache memory, is called main memory. It is the central storage unit of the computer system. It is a large and fast memory used to store data during computer operations. Main memory is made up of RAM and ROM, with RAM integrated circuit chips holing the major share.

1 RAM: Random Access Memory

DRAM: Dynamic RAM, is made of capacitors and transistors, and must be refreshed every 10~100 ms. It is slower and cheaper than SRAM.

SRAM: Static RAM, has a six transistor circuit in each cell and retains data, until powered off.

NVRAM: Non-Volatile RAM, retains its data, even when turned off. Example: Flash memory.

2 ROM: Read Only Memory, is non-volatile and is more like a permanent storage for information. It also stores the bootstrap loader program, to load and start the operating system when computer is turned on.

PROM(Programmable ROM), EPROM(Erasable PROM) and EEPROM(Electrically Erasable PROM) are some commonly used ROMs.