K e y b o a r d  

On the surface

Most common: 104 key Windows keyboard.

• keys
  • QWERTY -design (QWERTZ for German keyboards),
  • other layouts possible, like DVORAK
• Numeric keypad -- same layout like in adding machines and calculators
• Function keys -- top of keyboard (F1, F2, ...), specific commands for applications or OS
• Control keys
  • arrow keys
  • Ctrl, Alt, Esc, Insert, Delete, ...

Notebooks have fewer keys (mine has 84)---usually no numeric keypad.
Apple keyboards fewer keys as well
Variety of other keyboards available.

Underneath

Switches, connected to a microprocessor, one for each key.
Key "bridges" circuit
microprocessor observes these circuits and compares to "character map", also for combinations
Computer also has a character map
typematics: press key longer: what happens?

"Typewriter" mechanics

provides "feel" of a typewriter. Clicks, keys jump back, ...

Into the cable ...

• 6-pin IBM PS/2 connector
• 4-pin USB (Universal Serial Bus) connector
• internal connector (for laptops)

small amount of power comes from the computer to the keyboard
letter information is sent from the keyboard to the computer.
Sent is a string of 0s and 1s.
Characters are encoded as Bytes

Bits and Bytes I

Everything in computers is encoded as 1s or 0s, either through the cable or in storage.
Bit: either a "0" or a "1".
Byte: A package of 8 bits.
How many thing can you encode using 8 bits?
(Extended) Ascii code: Encoding of characters using a byte (sequence of 8 bits). For instance "A" is encoded as "65", "a" as "97".

Erich Prisner, August 2003