CH 4 STORAGE DEVICES Reference Book Computers for

CH 4 STORAGE DEVICES (Reference Book: Computers for Nursing by S. Y. Vaishampayan)

CONTENTS: • 1. 1 Introduction • 1. 2 In Detail

1. 1 Introduction: • It is necessary for every computer to have storage device to store data and programs. • Technologists have developed storage media to store data. The storage media is called “Storage Device”. Device • A computer can write data to and read from a storage device.

1. 1 Introduction: (CONTD. . ) • ‘Before shutting down a computer user can store his data and programs in storage devices’ like floppy in Diskettes and Hard Disks. • ‘The stored data can be used any time in future, can be further processed as per requirement’. These storing devices are called as “Secondary Storage Devices”. Devices • These Secondary Storage Devices are outside the CPU.

1. 1 Introduction: (CONTD. . ) • The Application Programs like Excel, Word can be stored in Secondary Storage Devices. • The Random Access Memory is used for internal temporary storage of data. • As soon as the computer is switched OFF the data in the RAM is lost. Hence it is called Temporary Data Storage Warehouse • The Primary Storage Capacity is not sufficient. Hence a Permanent Data Storage Warehouse OR a Secondary Storage is essential.

1. 2 IN DETAIL: : • TYPES OF DATA STORAGE DEVICES: A. HARD DISK B. FLOPPY DISK C. OPTICAL DISK D. MAGNETIC TAPE

A. HARD DISK: – A Hard Disk is a stack of one or more metal plates. – The speed and capacity of storage is more. – It is a very sensitive device. – The gap between the read/write head and the surface of the disk is very small of the order of 0. 000001 inch. Due to this there is a possibility of Head Crash. – A dust particle, a human hair or even finger print on the surface may bridge the gap, causing the head to crash.

A. HARD DISK: (contd. . ) – A Head Crash destroys the data and even the head also. It is very dangerous. – Fig:

B. FLOPPY DISK: • A Floppy Disk is a small and portable magnetic storage device. • Floppy Disk is often called ‘Diskette’ Diskette or ‘Disk’. Disk • Documents, Documents Spread-Sheets, Spread-Sheets and other types of files can be stored on it, and can be carried. • They are used for back-up • Disk is “a Thin, Circular, and Mylar Plastic, coated with iron oxide and encased in a plastic sleeve. ”

B. FLOPPY DISK: (contd. . ) • The Motor of Floppy Drive rotates the disk. • The Read/Write Head moves over the surface of the disk to read or write data. • The Read/Write Head passes over the disk surface. • Iron oxide particles are subjected to electromagnetic field produced by the electro magnet of the head.

B. FLOPPY DISK: (contd. . ) • The iron particles get magnetized according to the field applied to it. • They can be in ON or OFF state and data is stored in ASCII or EBCDIC format. • A floppy disk is also called as flexible disk, this is because of the plastic sheet inside plastic sleeve is not rigid but flexible.

B. FLOPPY DISK: (contd. . ) • Fig:

C. OPTICAL DISK: • Optical disk can store 4. 6 GB data. • This storage capacity means it can accommodate 10 lakhs of typed pages or all books of medium scale library. • In case of Optical Disk, Disk the Optical Storage Technique uses laser beam to read data. – For “Magnetic Storage Devices”, Devices 0’s and 1’s are stored by means of magnetic field. – While in case of “Optical Disks”, Disks the spot that reflects the laser beam is “ 1”, and the absence of reflection is “ 0”.

C. OPTICAL DISK: (contd. . ) • Data is stored on the metallic surface by means of two surfaces as follows: – Land: » This is the flat surface, which reflects beam. – Pit: » This is a depression or hollow surface, which does not reflect beam.

C. OPTICAL DISK: (contd. . ) • The Laser Beam is concentrated, focused on these lands and pits to read 1’s and 0’s • Optical Disks are available in different sizes and they are : (3. 5”, 3. 5” 4. 75”, 4. 75” 5. 25”, 5. 25” 8”, 8” 12”, 12” and 14”) 14” • The normal size of an optical disk is 4. 75 inch, inch which is used for different types of disks known as CD and DVD

C. OPTICAL DISK: (contd. . )

C. OPTICAL DISK: (contd. . ) a. Compact Disk (CD): – Compact Disk or CD is more popular. – In most of the computer system, CD drive is used as standard storage device. – Capacity of one side of the CD is 650 MB.

C. OPTICAL DISK: (contd. . ) a. Compact Disk (CD): (contd. . ) - The first CD-ROM drives read data at the speed of 150 KBps (Kilo bytes per second). - This speed is considered as single speed, and now the speeds are, 24 x (means 24 times single speed). - It will read 24 x 150 KB = 3600 KB i. e. 3. 6 MB (Mega bytes) and 36 x drive can read 4. 8 MB data.

C. OPTICAL DISK: (contd. . ) a. Compact Disk (CD): (contd. . ) – Types of CD’s: Types of CD’s CD-ROM CD-RW

C. OPTICAL DISK: (contd. . ) i. CD-ROM: – Abbreviation for “Compact Disk Read Only Memory”. Memory – It is just like CD’s of Music. – “Read Only” Only means, user cannot write

C. OPTICAL DISK: (contd. . ) ii. CD-R: - Abbreviation for “CD Recordable”. Recordable - It is also known as, ‘ WORM ’, that is “Write Once and Read Many”. Many - The data can be written on CD-R only once. - It can be read many times with same quantity. - These CD’s are used record selected songs and data is saved permanently.

C. OPTICAL DISK: (contd. . ) iii. CD-RW: - Abbreviation for “Compact Disk Re-Writable”. Re-Writable - They are also called as “Erasable Optical Disk”. Disk - These are similar to other optical CD’s but surface of disk is changed temporarily when data is stored in it. - The stored data can be changed, edited hence they are used in multimedia applications.

C. OPTICAL DISK: (contd. . ) b. Digital Versatile Disk (DVD): – They are also called as Digital Video Disk – DVD and DVD Drives, work similar to other optical CDs and drives, only difference is the storage capacity – One side of DVD can store 4. 6. GB data which is seven times that of other CD’s. – Most of the DVD drives write data on both sides of DVD, hence their storage capacity is doubled.

D. MAGNETIC TAPE: • Magnetic Tapes and Reels of magnetic tapes are used for Back-Up Purpose • The data from the media can be accessed by two methods: i. Direct Access Method ii. Sequential Access Method

D. MAGNETIC TAPE: (contd. . ) i. Direct Access Method: • The disk stores data along the sector of a particular track. • The location of a file or other information related to that file is used to access that file directly.

D. MAGNETIC TAPE: (contd. . ) i. Direct Access Method: (contd. . )

D. MAGNETIC TAPE: (contd. . ) ii. Sequencial Access Method: • In case of magnetic tapes, tape drive writes data sequentially i. e. one byte after another. Hence, data must be accessed sequentially which is slower than disks.

D. MAGNETIC TAPE: (contd. . ) ii. Sequencial Access Method: (contd. . ) • The magnetic tape is similar to audio tape recorder. The particular song from the cassette cannot be played at once, as sequence is to be checked for it. Then, knowing the sequence song can be selected.

D. MAGNETIC TAPE: (contd. . ) ii. Sequencial Access Method: (contd. . ) • Suppose, the information is stored on a magnetic tape with reference to ‘Alphabets’ sequence. Now, to access information related, the tape moves or scans from ‘A’ to ‘P’ first and then the information of ‘A’ will be available.

D. MAGNETIC TAPE: (contd. . ) ii. Sequencial Access Method: (contd. . )

D. MAGNETIC TAPE: (contd. . ) ii. Sequencial Access Method: (contd. . )

D. MAGNETIC TAPE: (contd. . ) • Sequencial Access Method: (contd. . )

Accessing Stored Data • We refer to a collection of data stored in a computer system as a ‘file’. file Files are often organized into ‘folders’. folders • Whenever you click ‘Save’ Save in an application, burn files to a CD-R, copy music onto your MP 3 player, or drag and drop a file onto memory stick, you are using storage devices - devices that can store and retrieve data.

Accessing Stored Data (contd. . )

Serial / Sequential Access • A serial (or sequential) access storage device is one that stores files one-by-one in a sequence. • A non-computer serial access device that will be familiar to you is a VHS videotape. Because video is stored on a long piece of tape, when TV shows are recorded onto the tape, they go on one-by-one, in order. . .

Serial / Sequential Access (contd. . ) • If you want to watch a show that you recorded earlier, you have to rewind / fast-forward through all other shows until you find it. • The shows are only accessible in the same order that you recorded them. This type of one-by-one storage and access is called serial access

Serial / Sequential Access (contd. . ) • Systems that store things on tape (video, music, computer data, etc. ) are always serial access

Direct / Random Access • A direct (or ‘random’) access storage device is one that stores files so that they can be instantly accessed there is no need to search through other files to get to the one you want. • An example of a direct access device would be a DVD movie. Unlike the VHS videotape movie, you can jump to any scene on a DVD. • All parts of the DVD are directly accessible. This type of file storage is called direct access

Direct / Random Access (contd. . )