Serial ports, a.k.a. RS232 ports, are no longer available on new computers and laptops. Many devices still use RS232 for communication (network equipment, data acquisition boards etc.).

There are several USB adapters that provide a “Virtual COM Port” using a special “USBtoUART” or “USBtoSerial” chip. Conversion cables containing these chips can be found online – but the documentation rarely specifies which chip is used! The Prolific PL-2303 chip is very popular, but a number of other chips can be found. Some chips are supported by the OS, others need a special driver.

Manufacturer Chip Linux driver Mac driver Windows driver
FTDI chip FT232RL Included since 2.6.31 kernel Download VCP driver Automatically installed by Windows 7
Prolific PL-2303 Included since 2.4.10 / 2.4.31 kernel Download VCP driver Installation under Windows 7
Silicon Labs CP210x Download VCP driver Download VCP driver Download VCP driver
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RS232 information

Updated 2011-06-01: Added links to Open Source driver for Prolific PL2303 under Mac OS X