This document summarizes various input and output devices for computers. It describes keyboards, mice, and scanners as common input devices. It notes that keyboards send signals when keys are pressed which are interpreted as letters or characters. Mice control cursor movement and are useful for graphics. Scanners scan images or text and convert it to a computer-readable format. For output, it discusses computer monitors for displaying content, speakers for audio output, and storage devices like floppy disks, CDs, DVDs, and removable disks for secondary storage.

1. UNIT II
INPUT AND OUTPUT DEVICES

2. INPUT DEVICES
Keyboard
 A particular key is pressed, sending an electronic signal to the computers
‘brain’.
 The computers ‘brain’ interprets the signal.
 The computer sends back a particular letter or character which represents
the signal that the computer has interpreted.

3. Mouse
 Controls the movement of the cursor on the screen – as you move the mouse,
the cursor moves in the same direction.
 Useful in graphics programs where you can draw pictures by using the mouse
a pen or paintbrush.
 So called because of it’s shape – the wire connecting it to the computer being
it’s tail.

4. Scanner
 Scans a picture or text.
 Translates information into a form the computer can understand.
 This information can then be
 displayed on the computer screen
 stored to a file
 used in computer documents

5. OUTPUT DEVICES
computer monitor
 The most obvious and useful output device, displaying text and
graphics as you are working on them.
 Can display still or moving images.
speaker:
 Speakers output sound from your computer.
 The speakers take the electronic signals stored on things like CD’s
and DVD’s and send them out as the sound we can hear.

6. Secondary storage device
Zip / Jaz Disks
 Similar to floppy disks
• They are removable
Their platters are made of a hard material
• Can operate at higher speeds than floppies.
 Newer standards hold more data
• Most people have outgrown floppy disks

7. Floppy Disk
 Floppy disks are similar to hard disks
 Because the medium is “floppy”, the disks cannot operate at the same speeds as a
hard disk.
 Floppy disks are older technology which haven’t received a lot of attention since
the late 1980s.
 Many computers today do not even come with floppy disk drives anymore.

8. OPTICAL DISK
 Optical disks are very much like hard disks.
 Hard disks store information using magnetic material
- Bits are stored by changing the magnetic properties of the magnetic material
- Bits are read by picking up the tiny magnetic field with a read head.
 Optical disks store information as pits in a physical medium
- A laser is used to determine if a pit is present or not.

9. CD ROM
CD Roms use the same technology as audio Compact Discs.
 A master disc is created.
 Copies of the disc are created through a pressing process
 The discs are aluminum sandwiched between plastic
 CDs are single sided.

10. CD-RW
 CD-RW is similar to CD-R
 The main difference is that the dye can be made reflective again
through an erase process
 In this way, CD-RW discs can be written many times
 Too much erasing, and the dye starts to fade.

11. DVD
 Each side of a DVD can contain 2 layers, doubling the amount of data that can
stored.
 One layer is semi-transparent. The laser can be focused “through” that layer
onto the second layer
 If you took the track off of a single layer of a DVD and stretched it out into a
straight line, it would be 7.5 miles long!.
 If you did the same with a double layer, double sided disc, the track would
stretch to over 30 miles!

12. DVD-R and DVD-RW
 These two technologies are still relatively new and still fairly
 DVD-R and DVD-RW use similar techniques as CD-R and CD-RW
 A dye layer is used for data writing
 The dye layer in DVD-RW is erasable