Machine-readable medium
In communications and computing a machine-readable medium, or computer-readable medium, is a medium capable of storing data in a format readable by a mechanical device (rather than human readable).

Examples of machine-readable media include magnetic media such as magnetic disks, cards, tapes, and drums, punched cards and paper tapes, optical discs, barcodes and magnetic ink characters.

Common machine-readable technologies include magnetic recording, processing waveforms, and barcodes. Optical character recognition (OCR) can be used to enable machines to read information available to humans. Any information retrievable by any form of energy can be machine-readable. 

Examples include:

Acoustics
Chemical
Photochemical
Electrical
Semiconductor used in volatile RAM microchips
Floating-gate transistor used in  non-volatile memory cards
Radio transmission
Magnetic storage
Mechanical
 Tins And Swins
 Punched card
 Paper tape
Music roll
 Music box cylinder or disk
Grooves  (See also Audio Data)
 Phonograph cylinder
 Gramophone record
 DictaBelt (groove on plastic belt) 
 Capacitance Electronic Disc
Optics
Optical storage
Thermodynamic

See also
 MARC standards
 Machine-readable passport
 Paper data storage
 Machine-readable data
 Machine-Readable Documents
 Symmetric Phase Recording

References

Computing terminology
Storage media
Optical character recognition