February 13, 2011

 CD-ROM

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CD-ROM stands for Compact Disk Read Only Memory is a type of secondary storage or optical disc that users can read only but not write or erase. Philips and Sony companies invented Compact Disc in year 1982. CD-Rom is a WORM (Write Once Read Many times) device.  Typically they can store up to 600-700 MB of data or 70 minutes of audio, also store video, data, and text. The diameter of a Compact Disk is 4.7 inches and its thickness is 0.047 inches. A single Compact Disk equal to : 1500 - 5.25-inch floppy disks, 450 - 3.5 inch floppy disks and 274,000 pages of text.


Types of Compact Disks :

(1)  CD-ROM     :  
Compact Disk Read Only Memory (Write Once Read Many times)

(2)  CD-R       :  
(Compact Disc-Recordable) WORM disks for Well known technology

(3)  CD-RW      :  
(Compact Disc-ReWritable) Rewritable and erasable.

(4)  CD Extra    :  
For Multimedia purpose. Developed by Sony, Philips and Microsoft.

(5)  CD-DA      :  
(Compact Disk Digital Audio) Audio CD, Digital Audio Developed by Philips and Sony companies.

(6)  Photo CD      :  
Developed by Kodak and Philips companies.

(7)  Video CD      :  
Can hold approximately 70 minutes of recorded video.

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 Floppy Disk

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Also known as a Diskette. The most common magnetic data storage medium used on computer is a floppy disk. These are made of an ultra thin, circular, Mylar plastic and coated with magnetic material. Floppy disks are commonly used as secondary storage and backup memory in a personal computer. These disks are very thin and flexible. It is cheaper than any other storage devices and portable. Data can be written (or) erased on a floppy disk.  In 1971, IBM introduced the 8 inch floppy disk, 1976, 5.25 (5¼) inch floppy disk were introduced by Shugart Associates and another most popular 3.5 (3½) inch floppy disk introduced Sony in 1980. The 3.5 (3½) inch floppy used in the ’A’ drive and the older 5.25 (5¼) inch floppy used in the ’B’ drive. The capacity of a 5.25 (5¼) inch floppy typically holds 1.2 mega bytes of information and each 3.5 (3½) inch floppy holds 1.44 megabytes of information. The advantage of floppy disks is that they can be removed from the computer and the data taken to another computer system.

There are three types of Floppy Disks available they are :

3.5" Floppy Disk
Capacity 1.44 Mb (Megabytes)
Introduced : Sony (1980)


5.25" Floppy Disk
Capacity 1.2 Mb (Megabytes)
Introduced : Shugart (1976)


8.0" Floppy Disk
Capacity 100 Kb (Kilobytes)
Introduced : IBM (1971)
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January 5, 2011

 Hard Disk

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The Hard drive also called the hard disk or fixed disk. This is the main storage for a computer and Non-volatile storage device. Every computer has a hard disk they are used to store the data files. Computers store information in two locations, First one, the computer’s RAM is used as a temporary storage location since whatever it contains is lost when the computer is powered off and Second one, Information that is stored permanently is written to the hard drive. Hard disk/Hard drive is different from RAM, because the information stays stored even if the power is turned off. Hard Drive can store a large amount of computer data in a small space and it storage provides faster access to files than a diskette.

Hard disks contain a number of magnetic platters that store information in the form of 0’s & 1’s and is stored in a series of concentric circles. A hard disk consists of one (or) more platters and several read/write heads that read and record data magnetically on platters, a stack of rotating disks inside the hard drive.  A read/write head is the device that reads the data from the disk platter into the computer.


Types of HDD (Hard Disk Drives) :
1.    IDE : Integrated Drive Electronics. it also known as PATA drives ( Parallel Advance Technology Attachment )
2.    SATA : Serial ATA or Serial Advance Technology Attachment.
3.    SCSI : Small Computer System Interface.
4.    SAS : Serial Attached SCSI.


Types of Hard Disk interfaces:

HD drives come in two main sizes, (i) 2.5" for laptops and (ii) 3.5" for desktops.

•    Desktop Hard Disk Types :- 3.5', IDE and SATA Interfaces.
•    Laptop Hard Disk Types :- 2.5', 1.8', IDE, SATA, SCSI.
•    Server Hard Disk Types :- 3.5', SATA, SCSI.
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December 30, 2010

 CD-ROM Drive

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CD ROM stands for "Compact Disc Read Only Memory".  A CD-ROM drive is the same size as a floppy disk drive.  It is a storage device that accepts data CD ROM’s (Compact Discs).  It is a box shaped device that fits into the case of the computer. A CD-ROM drive is an optical device which means it uses a laser to record information. Most new computers DVD drives have replaced CD ROM drives. A CD ROM drive will only play CD’s, not for DVD’s. 
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December 29, 2010

 Zip Drive

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Zip Drive introduced by Iomega Corporation in late 1994. Zip drive is a medium portable removable device looks like a floppy drive. A zip drive is needed to read and write 3.5 inch zip disk. Zip Drives are very expensive when compared to coast of other storage devices.



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October 28, 2010

 Storage Devices

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Secondary storage is also known as auxiliary memory or external memory or back up storage. The secondary storage devices are used in most computer systems to supplement the limited storage capacity of the primary memory section. This is similar to our keeping a diary or a note book when our memory is incapable of storing many facts and figures. We refer to our diary whenever we need the data.

Secondary Storage Devices are
1. Magnetic tape
2. Magnetic disks
3. Compact Disk Read Only Memory (CD-ROM)
The data is either stored or erased by laser beam to CD-ROM.

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Magnetic Tape:
Magnetic tap is one of the most popular storage medium for larger data that are sequentially accessed and processed. The tape is plastic ribbon usually 1/2 inch wide that is coated as one side with magnetic material. It is similar to the tape used on a tape recorder except that is higher quality and more durable.

Advantages
(a) Unlimited Storage Capacity
(b) Low Cost
(c) Portability

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Magnetic Disks :
A magnetic disk is a, circular plate coated on both sides with a magnetic material. It is very similar to a gramophone record. Each disk consists of a number of invisible concentric circles called tracks. Each track is further sub-divided into sectors. Information is recorded on the tracks of a disk surface in the form of invisible tiny magnetic spots. The presence of a magnetized spot is represents as '1 ' bit and its absence represented a '0' bit.

Magnetic disks are two types:
1. Floppy Disk
2. Hard Disk

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Floppy Disk:
The floppy disk is a flexible, circular shaped medium with a magnetic coating on it. It is sensitive to touch and dust. A floppy disk enclosed in a leather jacket to protect it from external damage and dust.

There are three types of floppy’s available.
1) 3.5" Floppy Disk ( Capacity 1.44 Mb ) introduced : Sony
2) 5.25" Floppy Disk ( Capacity 1.2 Mb ) introduced : Shugart
3) 8.0" Floppy Disk ( Capacity 100 Kb ) introduced : IBM

The 3.5" disks are the most popular and commonly used.

On the Basis of Capacity they are of two types:
(a) High density
(b) Low density

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Hard Disk:
Hard Disk is also a secondary storage device. The hard disk storage system was developed to reduce the problem of diskettes frequently getting damaged.

Hard disks come in different capacities. The minimum capacity is generally twenty times that of a high density floppy disk in terms of storage capacity. The hard disk is generally fixed inside the computers.

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Compact Disk Read Only Memory (CD-ROM):
CD-ROM disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. The storage density is very high, cost is very low and access time is relatively fast.

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Input/Output:
The term Input/Output is used to describe any program, operation or device that transfers data to or from a computer and to or from a peripheral device. Every transfer is an output from one device and an input into another. Devices such as keyboards and mouse are input-only devices while devices such as printers are output-only. A writable CD-ROM is both an input and an output device.

Input Devices:
Input device is a hardware device which is use to input data, image, and video to the computer.

Input Devices:
Digital camera
Keyboard
Microphone
Mouse
Scanner
Web Cam
Light pen
Joy stick
Etc.
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Out put Devices:
Output device is a hardware device which is use to receives or displays output from a computer

Output Devices:Monitor
Printer
Plotter
Speaker
Projector
Etc.


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