What is Computer Memory ? different types of memory ?

Short Term memory 
Random Access Memory ( RAM )

RAM read and write memory information can be written into and read from a RAM . it is a volatile memory it retains the stored information as long as it is supplied with power supply. when power supply is switched off or interrupted  , the stored information in the RAM is lost . 

RAM of various capacities are available . 

for ex :- 256 MB , 512 MB ,and so on .

Long Term memory 
Read Only Memory ( ROM ) 

ROM is a permanent type of memory . its contents are not lost when power supply is switched off . The user connot write into a ROM . its contents are written into at manufacturing time . ROM store permanent programs and other type of data which are needed by the computer to execute user program .

This can be removed by Flashing process .

Type of ROM 

• PROM  ( Programmable ROM )
• EPROM ( Erasable PROM )
• EEPROM ( Electronically Erasable PROM ) 

CACHE MEMORY

Cache memory is one of the main memory that are used frequently by CPU . The process can easily access that data in a shorter time  whenever the CPU needs to access the memory. it first check the cache memory , then the CPU moves into the the main memory . Cache memory is placed b/w the CPU and the main memory  . The cache memory is the fastest component in the memory hierarchy and approches the speed of CPU components .

Basic operation of a cache memory is as follow :-

• The  performance of the cache memory is frequently measured in term of a quantity called Hit Ratio .
• When the CPU refers to memory and finds the words in cache , it is said to Produce a hit .
• If the word is not found in the cache , it is in main memory and it counts as a Miss .

HARD DISK 

Hard disk is the device used for mass storage of data that stores on a hard disk can be retrieved at a very fast speed bring a direct address device , unlike flopples , CDS etc. you cannot easily remove hard disk from a PC.

SOLID STATE DRIVE  ( SSD )

• SSD ( solid state drive ) is also a non volatile storage medium that is used to hold and access data . unlike a hard drive , it does not have moving components , so offers many advantages over SSD , such as fastest access time , noiseless , oprationless power consumption and more .
• As the cost of SSD has come down it has become an ideal replacement for a standard hard drive in a desktop and laptop computers it is also suitable for notebooks and tablets that don't require lots of storage .