A physical keyboard that uses an individual spring and switch for each key. Today, only premium keyboards are built with key switches; however, they were also used in the past, such as in the Model M keyboard from IBM, which used buckling spring switches. Mechanical keyboards are very much appreciated by fast typists because they have a springiness and feel that is not the same as the low-cost membrane keyboard accompanying most computers.
Types of Mechanical Switches
CHERRY key switches are commonly used today, while Alps and other types were used in the past. Buckling spring key switches cause the spring to buckle outwards rather than compress downwards, providing a unique tactile feedback. See premium keyboard
and membrane keyboard
Das Keyboard Uses CHERRY Switches
Das Keyboards use CHERRY MX Blue or Brown mechanical key switches like these. The Blue switches have a "clicky" sound when the key is sufficiently depressed, while the Brown have a soft tactile bump. (Image courtesy of Das Keyboard, www.daskeyboard.com)
Buckling Spring Keyboard
Unicomp's keyboards use buckling spring key switches, popularized on IBM PC keyboards. Although the keys have a clicky sound, they also have a unique tactile feel that made IBM keyboards stand out.
Avant Stellar Keyboard
One of the finest keyboards ever made and lamentably discontinued, Avant Stellars were entirely programmable. They used Alps mechanical key switches.