Concept of memory(Primary and Secondary)

Memory-Memory is a storage area to store data, instruction, information, and reproduce these whenever desired.

Memory Units

1 Nibble = 4 bits
1 Byte = 8 bits

1 KB = 1024 bytes

1 MB = 1024 KB

1 GB = 1024 MB

* Note:- kb stands for kilobits/ KB stands for kilobytes

Memory is broadly classified into two types:

Primary memory or Internal memory.
Secondary memory or External memory.

PRIMARY MEMORY
Primary memory is also termed as Main memory or Internal memory. Main memory is the built-in memory where CPU holds the data and programs being manipulated currently.

Primary memory/Main memory can be divided into two types :

Random Access Memory (RAM)
Read-Only Memory (ROM)

RAM-RAM stands for Random Access Memory and it is a volatile memory. Volatile means that stored information or data is lost as soon as the power is turned off.

ROM-ROM stands for Read-Only Memory and it is a non-volatile memory. Means ROM retains its contents even when the computer is turned off and its contents can be accessed but cannot be changed.

DIFFERENCE BETWEEN RAM AND ROM

Sr. No.	RAM	ROM
1	It stands for Random Access Memory	It stands for Read-Only Memory
2	It is a volatile memory	It is a non-volatile memory
3	It is in direct contact with CPU	It is not in direct contact with CPU and its contents are first loaded to RAM
4	Its contents can be accessed as well as changed.	In general, its contents can be accessed but cannot be changed.

SECONDARY MEMORY

Secondary memory is not in direct contact with CPU, i.e. CPU cannot get data or instructions stored in this memory directly. For execution, these contents must be loaded to the main memory(RAM) of the computer. Secondary memory devices are used to store a large amount of data permanently.

Some most common secondary memory devices are:

1. Magnetic Media- Such as Floppy disk, Hard disk

Floppy Disk- Floppy disk is made up of a flexible substance called Mylar. Floppy disk has a magnetic surface that allows the recording of data. A standard floppy disk can store up to 1.44 MB of data.

Advantages

Floppy disks are cheap
Compact and portable

Disadvantage

Less storage capacity
Read/write head makes direct contact with the disk surface during the process of reading or writing. So it can be damaged with constant use.

Hard Disk- Hard disk drive is a pack of circular platters of plastic that is coated with magnetizing material and a magnetic head perform the job of reading and writing on the disk. A hard disk can store a large amount of data at a faster speed compared to floppy disk and CD-ROM.

Advantages

large storage capacity
Stores and retrieves data much faster than a floppy disk or CD-ROM
Permanent storage
Usually fixed inside the computer so don't get lost or damaged

Disadvantage

Far slower than RAM/ROM
The disk is fixed inside the computer and cannot easily be transferred to another computer.

2. Optical Media- Such as CD(Compact Disk) and DVD(Digital Video Disk)

Compact Disk- A compact disk is a small plastic disc that stores and retrieves data using laser light. Compact disk replaced floppy disk because CDs were faster and could hold more information up to 700 MB.

Advantages

Cheap
Small and portable

Disadvantage

Fragile
Slower to access than hard disk
Smaller storage capacity than hard drive or DVD

Digital Video Disk- DVD is a type of optical media used for storing digital data. Its size is also similar to a CD but has a larger storage capacity of up to 4.7 to 9 GB.