2. Input, Output and Storage GapFill

A vast range of input, output and storage devices exist to cater for a vast range of situations in which they might be needed. OCR, the acronym for  opticaloptronicobservationaloperand character recognition can be used with scans of documents and handwriting from flatbed scanners.  Barcode scanners require line of sight to their targets, and measure the  microwavesradiationinterferencelight reflected back, although they're actually scanning the gaps between the bars rather than the bars themselves.  If you want an input device capable of scanning a card while it's still in someone's wallet or pocket, you're looking for  RIDFRDFIRFDIRFID technology.  Used in conjunction with  biometerbiometricbiochemicalbiological scanners, such as fingerprint scanners, as a means of authenticating people they can make a site quite secure.  Some input devices are more subtle such as those in  scannerstablesfitness trackersspeakers which may have, for example, temperature and GPS  sensorsmethodologiesmicrophonesstraps built in.

In terms of output devices, most people are familiar with printers, but fewer people have used a  engravercutterscriberplotter, which entails a robotic arm holding a pen, highly useful for  colour gradients3D printingartistic reproductionstechnical drawings.  For visual outputs, one measure of the quality of a screen is DPI, which stands for  derived pixel indexingdata points per inchdots per inchdensity of pixels per inch.  A higher number is better, although too high and you've gone beyond the range of human perception.  Another measure is the resolution, measured pixels wide by pixels high.  Increasingly common is 4K resolution, which is 3840 x 2160.  Screen size itself is another measure, and this is a measure of  the visible screen taken horizontallythe visible screen, taken diagonallythe visible screen taken verticallythe whole unit, taken diagonally.  Some devices are classified as hybrid, meaning they act simultaneously as both an input and an output device.  Included among these are  speakersmiceGPS sensorstouchscreens and some  dedicated microphonesvideo cardsprojectorsgames controllers.

Storage devices are also quite varied, although magnetic remains popular due to its relatively low cost.  A magnetic drive contains a series of double-sided disks called  leavesplatterslaminasstrata, which rotate, and a read/write  nodenoduleheadmodule, whose job is to load and save data to the disk.