What is Computer Memory ? Describe of Memory classification?

Introduction:
One of the major advantages of computer is its storage capacity where huge amount of information can be stored,but how this information is represented and stored? In this chapter,we are going to learn about the various data storage devices and the units which are used to measure the stored data.

In the previous chapter,we studied the different types of input devices. But when the data and instructions are entered in the computer, Where they are stored.In fact, inside the computer, there are different storage areas where it keeps data or information permanently or temporarily while working. This storage area is known as the Memory of the computer.
A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer,

The memory of the computer is divided into two categories:

1. Primary Memory

2. Secondary Memory

Primary Memory:-
This is the main memory of the computer. CPU can directly read or write on this memory. It is fixed on the motherboard of the computer.
Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory.
A computer cannot run without the primary memory.
Primary memory is further divided in two types:

A) RAM (Random Access Memory)

B) ROM (Read Only Memory)

A) RAM (Random Access Memory):- 

RAM is a temporary memory. The information stored in this memory is lost as the power supply to the computer is turned off. That's 

why it is also called Volatile Memory. It stores the data and instruction given by the user and also the results produced by the computer temporarily.

B) ROM (Read only Memory)
Information stored in ROM is permanent in nature,i.e., it holds the data even if the system is switched off. It holds the starting instructions for the computer. ROM cannot be overwritten by the computer. It is also called Non-Volatile Memory.

Secondary Memory:-
This memory is permanent in nature. It is used to store the different programs and the information permanently (which were temporarily stored in RAM). It holds the information till we erase it.

Different types of secondary storage devices are:

Hard Disc, Compact Disc, DVD, Pen Drive, Flash Drive, etc.
Harddisk:
This is the main storage device of the computer which is fixed inside the CPU box. Its storage capacity is very high that varies from 200 GB to 3 TB. As it is fixed inside the CPU box.

Compact Disk:
It is a thin plastic disc coated with metal. Computer can read and write data stored on it. This is an optical storage device with a storage capacity of up to 700 MB and it can store varieties of data like pictures,sounds,movies,texts,etc.

CD-ROM:
CD-ROM refers to Compact Disc-Read Only Memory. Data or information is recorded at the time of manufacturing and it can only be read. A CD-ROM cannot be used to record fresh data by the computer.

CD-R:
CD-R is the short form of Compact Disc-Recordable. Data can be written on it once and can be read whenever required. The data written once cannot be erased.

CD-RW:
CD-RW stands for Compact Disc Re-writable. CD-RW can be used to write information over and over again,i.e,previous information can be erased and new information can be written on it using a CD writer fixed inside the CPU box.

DVD:
DVD stands for Digital Versatile Disc. It is an optical storage device which reads data faster than a CD.A single layer,single sided DVD can store data up to 4.7 GB,i.e,around 6 times than that of CD and a double layer DVD can store data up to 17.08 GB,i.e.,around 25 times that of CD. Though DVDs look just like CDs,they can hold much more data,for example,a full length movie.

Flash Drive:
It is an electronic memory device popularly known as pen drive in which data can be stored permanently and erased when not needed. It is a portable storage device that can be easily connected and removed from the CPU to store data in it. It's capacity can vary form 2 GB to 256 GB.

Blue Ray:
This is a newly invented optical data storage device whose storage capacity can be form 25 GB up to 200 GB. It is mainly used to store high quality sound and movie data. They are the scratch resistant discs,that’s why,storing data on these is much safer than a CD OR DVD.

So,these are some the common devices we use to store information and data in the computer.

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