A computer keyboard is an "Input" device and is used for input of text and characters and also to control the operation of a computer. It partially resembles a typewriter keyboard. Most keys on the keyboard correspond to a single written alphabet/number/symbol/command. However, to produce some symbols/command, pressing and holding of two or more keys simultaneously or in sequence is required. Some keys do not produce any symbol, but instead affect the operation of the computer or the keyboard itself.
1. Difference in Connection to Motherboard: Keyboards come in "AT", "PS2" and USB connection types which are connectible to "COM", "PS2 Keyboard" and "USB" ports of the motherboard respectively. 2. Difference in Design :
i. Membrane Type: Membrane Type keyboards are by far the most commonly used. They are designed in a way that all the keycaps are positioned above rubber domes, which are above a 3-layer plastic membrane that spreads over the entire keyboard. When the user presses the keycap, a contact point at the top of the rubber dome pushes the top layer through a hole in the middle layer to contact the bottom layer, creating a short circuit which generates the keystroke. The middle layer of the membrane keeps the top and bottom layers from contacting each other except when a key is depressed. The elasticity of the rubber dome membrane returns the key to its default 'up' position. Membrane keyboards are typically inexpensive and can have firm or soft feel depending on the design of the rubber domes. Membrane keyboards also come in foldable types. These keyboards are not durable and sturdy like cherry type keyboards.
ii. Cherry Type: Cherry Type keyboards are more rigid and sturdy but are usually heavier and costlier. Each key has its own independent keyswitch mechanism that will register when a key is pressed. These keyboards are more durable and are of higher quality than membrane keyboards but are usually heavier and costlier.
iii. Wireless keyboards: Wireless keyboards have become popular for their increased user freedom. However, wireless keyboards need batteries to work and are costlier.
iv. Laser Keyboard: These keyboards work by projecting an image of a full size keyboard onto a surface. Sensors in the projection unit identify which key is being "pressed" and relay the signals to a computer or PDA. These keyboards are also costlier.
Keyboard Keys Layout: The lay out of keys in standard keyboards generally follow QWERTY layout model and have 101 keys. Some keyboards have additional shortcut keys for multimedia and other operations.