Mechanical media

Mechanical media physically alter the media during the recording process. Examples include music boxes, punched tapes and cards, piano rolls, LP records, and the "pits" formed by lasers in optical write-once-read-many times (WORM) drives.

Mechanical media use some form of movement between the medium and a physical, tracking device. The tracking device reacts to the differences in the medium as it moves past. For example, a music box moves a disk or drum across tuned metal strips that convert the information coded by the presence of a pin or no pin into audible sound.

The tip of the SPM uses a mechanical technique similar to the music box to read information about the surface of a sample. The tip of the SPM contacts the surface of the sample and variations in the surface generate minute pressure on the peizoelectric crystal backing. The minute changes in pressure caused by surface variations generate small amounts of energy in the crystal, which are then amplified and analyzed to depict the surface of the sample.

Magnetic media

Magnetic media encode data on magnetic material or coating by altering magnetic fields with a recording head. Examples include magnetic tape, data strips on credit cards, hard and floppy disks, random access memory (RAM), and bubble memory.

Magnetic media rely on hysteresis, the ability of some material to remain magnetized. To record information, an electrical signal is sent through small coils in the head, creating a small magnetic field that alters the magnetic media. To read recorded information, the coils in the head react to the magnetic fields of the media, generating small currents that are amplified and ordered to reconstruct the information.

Hysterisis Animation

The heads on a magnetic audio tape recorder are static and the recording medium travels past stationary recording and playback heads. Video and other helical scan recorders incorporate moving recording heads in addition to the tape movement. Magnetic disks also move both the medium and the recording/playback head

Optical media

Optical media encode data by altering reflectivity, transmission, or other optical characteristics of the material. Examples include compact disk, read-only-memory (CD-ROM), digital video disks (DVD), and holograms.

Videodisc

Optical media use a variety of methods to change the reflection or transmission of light to represent the data. CD-ROMs use the presence or absence of a pit to indicate a binary 0 or 1 to encode data. Recordable optical media use techniques such as burning holes into the media, or creation of crystal structures with different reflecting properties to encode the 0s and 1s.

Movement

In virtually every data storage format, movement is critically important to recording (encoding) and retrieving (decoding) information. The greater the density of the data, the more critical the alignment between the record and playback head and the encoded data. Today, computer data tracks are approximately 0.65 um wide so coordination of the head movements and media must be extremely precise.

Surface of a CD

Speed

Speed is a critical element in accurate data retrieval. The correct relationship between the head and data tracks requires accurate disk speed. Digital data formats use speed to determine the beginning and end of data packets and location on the recording media. So, variations in speed can radically alter the way the original data is interpreted during retrieval.