Input Devices - Upgrading and Repairing PCs - page 749

Figure 15.5. Force levels used on KeyTronicEMS keyboards with Ergo Technology.
Perhaps the most well-known type of membrane keyboards are the IBM/Lexmark “Model M”
keyboards, which combine IBM's legendary buckling spring design with a high-end membrane
switch. To find the best membrane keyboards from the vast numbers on the market, look at the
lifespan rating of the keyswitches. Longer-lasting keyswitches make the keyboard cost more but will
lead to a better experience over the life of the keyboard.
Buckling Spring Capacitive and Membrane Switches
The keyboard included with the original IBM PC, XT, and AT systems used capacitive switches
combined with a buckling spring mechanism to provide the ultimate in performance and tactile
feedback. Capacitive switches are technically the only truly nonmechanical keyswitches in use today
(see Figure 15.6 ) . Although the movement of the key and buckling spring is mechanical in nature, in
the original designs these components do not close a mechanical contact or switch. Because of the
high cost of the capacitive switches, IBM switched its buckling spring keyboards from capacitive to
membrane switches in the mid-1980s. However, unlike more common membrane keyboards, all
buckling spring keyboards feature extremely high-end designs. Regardless of whether capacitive or
membrane designs are used, buckling spring keyswitches are considered to be among the best in the
world, offering the highest-quality tactile feedback of any type of switch. They are called buckling
spring keyboards because of the coiled spring and rocker used in each keyswitch to provide tactile
and audible feedback.