Pakistan study notes for Matric, Intermediate, B.A, B.COM BSC, M.A, BCS. Free Pakistani Urdu educational school, colleges and University notes.


Q.14. Which devices are used as an input device as well as output device? Define it in detail


Dual purpose de ices are devices that are input and output devices at the same time e.g disk drive and CD writer.


Disk drive is a peripheral device that reads or writes the disks (hard disks. floppy disks. etc.) that store information. Disk drives are called storage devices” because the store information on portable or permanent disks. The drive contains a motor to rotate the disk at a constant rate and one or more read/ write heads, which are positioned over the desired track. When the disk drive is used to read some data from a disk, it will fall in the category of input devices: while during writing data onto the disk, it will be considered as an output device.


In order for a disk drive o start to read or rite at a given location a read/ write head must be positioned radial over the right track and rotationally over the start of the right sector.


Radial motion is known as seeking’ and it is this which causes most of the noise heard during disk activity. There is usually one head for each disk surface and all heads move together.


The set of locations which are accessible with the heads in a given radial position is known as a “cylinder’.

Seek Time

The ‘seek time’ is the time taken to seek a different cylinder. The disk is constantly rotating and the read/ write heads move forward and backward until the desired location is found.


A CD writer is a device connected to our computer which can write on CD-RW and CD-R discs. CD-RW discs may be written, erased and rewritten, while CD-R discs may be written only once. CD writer performance is measured in “X” units, here I X = 150 kilobytes/ second. This allows users to ‘master’ a CD-ROM or audio CD for publishing. CD-R drives car also read CD- ROMs and play audio CDs.

The CD writer is also called a CD-R drive (short for Compact Disk—Recordable drive).

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