Pointing devices are connected to the computer using a USB, PS/2, serial, or bluetooth
connection. The data rate is very low, so USB pointing devices always run at
low speed (1.5 Mbps) even when they are certified to USB 2.0 standards. PS/2 and
serial interfaces are electrically identical but have different connectors; you can buy
adapters to convert one to the other.
A few years ago, there were dozens of communication protocols used by mice. Fortunately,
almost all mice now use an extended version of the PS/2 mouse protocol,
regardless of how they are connected, though graphics tablets, touch screens, and the
other more exotic pointing devices still use unique protocols.
By far the most popular pointing technology is now the optical mouse. Invented by
Agilent (formerly HP), an optical mouse contains a simple high-speed monochrome
video camera, a Digital Signal Processor (DSP), and interface electronics, all on a single
chip. The video camera acquires images of the desk or mousepad at the minimum
rate of 1,500 frames per second, and the DSP compares each frame with the
previous frame to detect movement. When movement is detected, it is communicated
with the host computer through the interface electronics, which may be serialor
radio-frequency-based (RF).
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