Storage is the act of keeping or information for future use or refonces. Parts of the computer use forkeeping data or information are known as storage device. It also known as secondary auxiliary or volatile or non-volatile storage devices. They store data or information for a long period of time and even when there is no power.

I. Reason for the need of secondary storage devices in the computer.

• Reason for the need of secondary storage devices in the computer To increase the speed of accessing data and information.

A. CASH MEMORY

It is a high speed temporal memory located on the CPU. It is use to store instruction that are required to run programs so as to improve the over roll speed of the computer. This memory allows quick access to data by the CPU, by storing data from the RAM memory in the cash; the CPU clock is very fast whereas the RAM access time is slow. It is very expensive to produce primary memory like RAM also the cost per bits of storage is very high.

B. DISK FORMATING

It is the act of dividing a disk into storage location called track and sectors for easy recording and retrieving of information (write and reading) of information that is this technique organized the disk into track and sector so as to easily store data and find any piece of data when needed.

Track: it is a narrow recording circle located on the surface of the disk that result from formatting process

1. A sector: is a pie-shape section on a track use to store a fixed amount of data.

Fig:

3. Cylinder: it is a collection of tracks with the same distance for all the platter.

IMPORTANT OF FORMATING DISK

• This process help to race any information previously store on the disk
• It helps to create file system (is a system that provide structures and role for encoding, storage and management of files stored on the disk.) examples of file system include:

• FAT meaning file allocation table created on smaller storage media and used by operating system like Ms Dos
• NTFS meaning new technology file system and used by operating system like Windows XP, Windows 7, 8
• HPFS meaning high performance file system and used by window NT
• EXT32 created on hard large disk used by units.

II. ACCESS STORAGE AND DATA ORGGANISATION

           1. Access time

It is the time taken for the read/write head to locate the file stored on the disk. It is usually measured and express in nano-seconds (fraction of a second). There are many types of storage device which have its own access time, there are two main methods for organizing files on a disk, these methods are:

a.Sequential file organization: it refers to the techniques of storing and retrieving data file one after another in a predetermine order on a storage device. to access or locate a file requires searching through the files until the desired file is located

b.Random access or direct access method: it is the technique of storing and accessing file anywhere and in any other in the disk. Drives are devices that read data stored on the disk or write data to a disk. The time taken access a file is very short for random storage device while for sequential storage devices it is very long. Sequential storage device has larger storage capacity while random access storage device have smaller storage capacity.

III.  STORAGE CAPACITY

It refers to the total amount of data or information, a storage device can hold usually express and measured in byte which is used to express the amount of space occupied by a file or the storage capacity of a disk.

A letter of alphabet including symbol is represented with 8 bits or 1 byte. Calculate the amount of spaces occupied by the following phases in the computer storage device.