Keyboards

Early computer keyboards had a layout taken from the TeleType teleprinter. The existence and position of the Esc (escape) and Ctrl (control) keys betray this. IBM moved the Esc key to its current position to make room for the Caps-Lock key and added the Alt key and other modifications.

Quick facts:

• Early PC keyboards had a full-sized 5-pin DIN connector.
• The AT keyboard was electrically different from the PC and XT keyboard. In the 1980s and early 1990s, many keyboards had an XT/AT switch and could be used on either system.
• The PS/2 keyboard has a 6-pin mini-DIN connector.
• The AT and PS/2 keyboards are electrically identical. A passive adapter can adapt an AT keyboard to a PS/2 connector and vice versa.
• Virtually all new keyboards are USB keyboards.
• Many people write their system password on the bottom of their keyboard.
• Some keyboards have multimedia keys, internet keys, or other special keys. These need a driver for the special keys to work.

Keyboard with multimedia and internet keys

• There are many types of switches used in keyboards.
  • Some keyboards have tall keys, and others have flatter keys. You may find the flatter keys on desktop keyboards, but they are usually used for notebook computers.
  • Some keyboards have metal contact switches for each key.
  • Some keyboards have flat membrane switches where sections of conductive plastic are pressed together through holes in an insulating separator.

Diagram of a membrane keyboard switch. The arrow shows where the key presses.

• Others have carbonized rubber contacts.

Carbonized rubber keyboard switches with contacts below.

A flexible keyboard. Yes, this is real–like typing on an overripe peach.

•  Some keyboards have capacitive sensors.
•  Some keyboards have hall effect sensors.

•  One company made a keyboard where every key had a tiny programmable LCD screen. It costs more than $1,000.00 U.S. Another company made a keyboard where each key had an E-ink display.
•  Yet another company makes a keyboard projected onto your desktop using a scanning laser. It is sold under several brand names for about $45.00 U.S. A camera in the projector senses finger movement.

Laser Projection Keyboard

Wireless mice and keyboards

Wireless mice and keyboards may use wireless USB (obsolete), Bluetooth, or a proprietary system. They also may use radio or infrared, but radio is the most common. The wireless mouse or keyboard receiver may connect by PS/2 connector (obsolete) or USB, but USB is virtually universal.

Wireless mice and keyboards must be paired to get them to communicate. With Bluetooth mice and keyboards, this is done as usual. With other wireless mice and keyboards, pairing is usually done by pressing a button on the receiver and then quickly pressing a button on the mouse or keyboard. However, some mice and keyboards are auto-pairing and require no action from the user to pair.

The IBM PCjr keyboard used infrared light to connect to the computer. Engineers never considered that multiple PCjr computers would be used in the same room, so they didn't encode the signal or take other steps to separate one signal from another. This was problematic when schools placed multiple PCjr computers in classrooms.