What is Storage?

2.1 Storage

Storage is also known as secondary storage, auxiliary storage, or mass storage. It is used to store data, information and programs permanently.

Different storage medium are used to store data, information and programs. It is called nonvolatile because its contents remain safe even if the computer is turned off. A hardware unit used to store and retrieve data to and from a storage medium is called storage device. Storage devices are available in different sizes and capacities. Storage devices include hard disk drives, optical discs and USB flash drives. Storage is required for the following reasons:

·         The main memory is a temporary memory. A storage device is required to store data and programs permanently.

·         The capacity of main memory is limited. A storage device is required to store a large amount of data and programs.

Two important functions of storage device are reading and writing.

·         Reading: The process of copying data, instructions or information from storage medium to memory is called reading.

·         Writing: The process of copying data, instructions or information from memory to a storage medium is called writing.

The time in which a device locates an item on a storage medium is called access time.

Access time of storage devices is slower than memory. The number of bytes that can be stored on a storage medium is called its capacity.

2.1.1 Basic Units of Data Storage

The basic units of data storage are as follows:

·         Bit: Computer works with binary digits. These digits are in the form of 0’s and 1’s. A binary digit is called bit. One bit takes one storage location in memory. It is the smallest unit for data storage.

·         Byte: A collection of eight bits is called byte. It is used to store single character.

·         Kilobyte: A kilobyte consists of 1024 bytes. It is denoted by KB.

·         Megabyte: A megabyte consists of 1024 kilobytes. It is denoted by MB.

·         Gigabyte: A gigabyte consists of 1024 megabytes. It is denoted by GB.

·         Terabyte: A terabyte consists of 1024 gigabytes. It is denoted by TB.

·         Petabyte: A petabyte consists of 1024 terabytes. It is denoted by PB.

·         Exabyte: An Exabyte consists of 1024 petabytes. It is denoted by EB.

·         Zettabyte: A zettabyte consists of 1024 exabytes. It is denoted by ZB.

·         Yottabyte: A yottabyte consists of 1024 zettabytes. It is denoted by YB.

2.1.2 Levels of Storage Hierarchy

The three levels of storage hierarchy are:

·         Online storage: It is directly available such as hard disk. Requires no special action on the user’s part to enable it.

·         Near-online storage: It is not directly available but can be made available by a simple action such as inserting a disk.

·         Offline storage: It is also called tertiary storage or archival storage. It is not readily available to the computer system. The devices such as tape backup units store data for archival purposes.

2.1.3    Difference between Memory and Storage

The difference between memory and storage is as follows:

Memory

1.       Memory is volatile.

2.       It is faster than storage.

3.       It is more expensive than storage.

4.       It is smaller in size than storage.

5.       Programs are copied from storage during execution.

6.       The capacity of memory is less than storage.

Storage

1.       Storage is nonvolatile.

2.       It is slower than memory.

3.       It is less expensive than memory.

4.       It is bigger in size than memory.

5.       Programs are stored in storage when no execution takes place.

6.       The capacity of storage is much more than memory.