How are Data Stored

How are Data Stored

A storage device is anything that is used to store computer data, such as Floppy disks, hard disks, optical disks, CDs and magnetic tapes.

Physical storage refers to how data are actually kept on the storage disk. The most commonly used medium for storage is magnetic storage

With Magnetic storage, the computer stores data on disks and tape by magnetizing selected particles of an oxide-based surface coating. The particles retain their magnetic orientation until that orientation is changed. Thus, magnetic disks and tapes are modifiable storage media.

The two most popular types of magnetic storage media are hard disks and diskettes. Magnetic tape provides a third type of magnetic storage, and optical disk is a new storage medium.

Hard drive The storage area within the computer itself, where megabytes of space are available to store bits of information. This is also known as a hard disk. Hard drive or hard disk storage provides faster access to files than a diskette. A hard disk platter is a flat, rigid disk made of aluminum or glass and coated with a magnetic oxide. A hard disk consists of one or more platters and their read-write heads. A read-write head is the device that reads the data from the disk platter into the computer. It also records (or writes) data onto the platters.

Hard disk platters in microcomputers are typically 3 inches (about 10 centimeters) in diameter: the same size as tho circular mylar disk in a diskette. However, the storage apacity of a hard disk far exceeds that of a floppy disk. Also, the access time of a hard disk is significantly faster than a diskette. Unlike diskettes, which begin to rotate when one requests data, hard disks are continualy in motion, so there is no delay as the disk spins up to speed. Like diskettes, hard disks provide random access to files by positioning the read-write head over the sector that contains the requested data.

Diskette A small, removable, flexible mylar plastic disk covered with a thin layer of a magnetisable substance, onto which digital data can be recorded and stored. This is also known as a floppy disk. Diskettes get another name floppy disk - from the thin mylar disk. Diskettes are also called floppies. Although today's microcomputers typically use 3% inch (about 10 centimeter) disks, you may still find 5% inch (about 15 centimetre) disks that were popular many years ago. Though, finding a disk drive to read 54 inch disks may be very difficult.

Diskettes are generally used for transporting or shipping data files or for making duplicate copies of data files for back-up purposes. The storage capacity of a diskette varies but is considerably smaller than that of a hard drive. Since the 960s, magnetic tape has been a popular form of mainframe

Computer storage.

Magnetic tape A continuous plastic strip covered with magnetic Oxide; the tape is divided into parallel tracks onto which data may be recorded by selectively magnetising parts of the surface, or spots, in each of the tracks. The data can then be stored and reused.

Sequential access means that data is stored and read as a sequence of bytes along the length of the tape. To find a file stored on a microcomputer tape storage device, one has to advance the tape to the appropriate location of the file, then wait for the computer to slowly read each byte until it finds the beginning of the file. Like an audio cassette, for example, a user must go through the tape in sequence to find the part he or she wants.

Microcomputer users quickly abandoned tape storage for the convenience and speed of random access disk drives.

Recently, however, tape storage for microcomputers has experienced a revival, not as a principal storage device but for making backup copies of the data stored on hard disks. The data on magnetic storage can be easily destroyed, erased, or otherwise lost. Protecting the data on the hard disk is of particular concern to users because it contains so much data, which could be difficult and time consuming to reconstruct. This is why backups are so important.

Diskette/Floppy Disk

Disk Format

All magnetic disks have the similar formats as explained below

Tracks A track is a circular ring on one side of the disk with each track having a number.
Sectors A disk sector is a wedge shaped piece on the disk.
Clusters A cluster is a set of track sectors, ranging from 2 to 32. One cluster is the minim space used to read or write anything on the disk.
Cylinders A cylinder is a set of matched tracks.

What happens when a disk if Formatted

All data stored on it get erased.
A Root Directory is created to record/list the content on the disk
Entire surface is checked for magnetic or physical defects.

Back up To copy a computer file or collection of files to a second medium, usually on a diskette or magnetic tape, so that the data are safe in case the original file is damaged or lost. Backups are usually copied to storage devices that can be removed rom the computer and kept separately from the

original.

A tape backup is a copy of the data from a hard disk, stored on magne tic tape and used to recover lost data. A tape backup is relatively inexpensive and can avoid the overwhelming task of trying to reconstruct lost data. Backing up electronic data is critical to protecting itfrom loss or damage.

The most popular types of tape drives for microcomputers also use tape cartridges, but there are several tape specifications and cartridge sizes. A tape cartridge is a removable magnetic tape module stmilar to a sound or video cassette tape. Quarter inch tape, called QIC, is a tape cartridge that contains 4 inch (approximately 2 centimetre) wide tape. Depending on tape length, QIC tape capacities range from 340 MB to 2 gigabytes.

Digital audio tape, called DAT (tapes), was originally an audio recording format, but is now also used for data storage. The 4mm wide DAT tape format storage capacity ranges from 2 gigabytes to 12 gigabytes

Optical Disk

A storage device that uses reflecting surfaces and laser technology to read and write data on a disk. This is also known as a laser disk. With optical storage, data is burned into the storage medium using beams of laser light. The burns form patterns of small pits in the disk surface to represent data. The pits on optical media are permanent, so the data cannot be changed. Optical media are very durable, but they do not provide the flexibility of magnetic media for changing the data once they are stored. It is not sensitive of touch as it can be easily cleaned.

There are three types of optical disks

1. CD-ROM's are the most popular type of optical storage. CD-ROM stands for Compact Dise Read Only Memory. A computer CD-ROM disk, like its audio counterpart, contains data that has been stamped on the disk surface as a series of pits. To read the data on a CD-ROM an optical read head distinguishes the patterns of pits that represent bytes. CD-ROM disks provide tremendous storage capacity. CD-ROMs usually come with data already written onto them. These days most applications software is provided on CD-ROM.

2. WORM DISKS It is now possible for computer users to write data to an optical disk. These are known as WORM disks, which stand for Write Once Read Many' A single CD holds up to 680 megabytes, equivalent to over 300,000 pages of text in character format, and these disks are quite durable. These CDs are known as CD re-recordable (CD-R). There are other types of WORM disks, although there is no standard for these.

3. CD-RW There is a third type of optical disk which can be erased and put to use to rewrite new information. These are sometimes known as EO (erasable optical) disks and CD-RW (CD rewritable).

Magneto-optical disks combine magnetic disk and CD-ROM technologies. Like magnetic media they can read and written to and like floppy disks they are removable. They can store over 200 MB of data, and speed of access to this data is faster than a floppy but slower than a hard drive.

CD-ROMs and magnet-optical disks are very useful for storing images. These take up much more storage space than data in character format, such as in word-processed files.

Other Devices

Flash Memory These are solid state devices which can read and write data electrically instead of magnetically. Electronic products, such as Camcorders, Digital cameras uses Flash memory cards.

USB Drive Known as Flash Drive, Thumb Drive, Key Drive etc., these are small in size and is used by plugging on the USB port on a PC. These hold memory storage capacity of 8 MB to as high as 1 GB.

Removable Hard Disk These compress data and are used as External hard drives to store back-up data of larger capacities going up as high as 1 tera-bytes.

Optical Cards A chip embedded on such cards hold personal data and information and records. These are used as a Smart card and used for financial and /or commercial transactions.

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tradeimexinfoDecember 31, 2020 at 2:23 AM
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