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other keys can perform double duty (such as having a numeric
keypad function embedded within the main keyboard keys).
Most keyboards attach to the PC via a PS/2 connector or USB
port (newer). Older Macintosh computers used an ABD connector,
but for several years now all Mac keyboards have connected using
USB.
Pointing Devices
The graphical user interfaces (GUIs) in use today require some
kind of device for positioning the on-screen cursor. Typical pointing
devices are: mouse, trackball, touch pad, trackpoint, trackball,
graphics tablet, joystick, and touch screen.
Pointing devices, such as a mouse, connected to the PC via a
serial ports (old), PS/2 mouse port (newer), or USB port (newest).
Older Macs used ADB to connect their mice, but all recent Macs use
USB (usually to a USB port right on the USB keyboard).
Scanners
A scanner is a device that images a printed page or graphic by
digitizing it, producing an image made of tiny pixels of different
brightness and color values which are represented numerically and
sent to the computer. Scanners scan graphics, but they can also scan
pages of text which are then run through OCR (Optical Character
Recognition) software that identifies the individual letter shapes and
creates a text file of the page's contents.
Microphone
A microphone can be attached to a computer to record sound
(usually through a sound card input or circuitry built into the
motherboard). The sound is digitized—turned into numbers that
represent the original analog sound waves—and stored in the
computer to later processing and playback.
MIDI Devices
MIDI (Musical Instrument Digital Interface) is a system
designed to transmit information between electronic musical
instruments. A MIDI musical keyboard can be attached to a
computer and allow a performer to play music that is captured by the

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