You can probably instantly recognize the USB, microphone, printer, speaker, SD card and power connectors found on your PC. Older computers, however, often have legacy ports that you may not need or even be familiar with. For instance, many computers come equipped with one or more general purpose, 9-pin outlets that may not fit any peripheral devices you currently use. At one time these performed many different functions that were essential to the way computers were used.
Video Monitor Ports
Many older desktop PCs have a 9-pin, female VGA outlet used to connect their video card or onboard, integrated graphics system to an external monitor. Although a laptop, notebook or netbook has a built-in display, it may also have a 9-pin outlet that enables you to use an alternative display device like a portable projector, CRT or LCD monitor. In newer PCs, the 9-pin VGA outlets have been replaced by or supplemented with High-Definition Multimedia Interface display connectors.
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DB9 Serial Ports
Many early PC designs used DB9 serial ports to communicate with other computers or hardware devices. This 9-pin layout become a de facto hardware standard that enabled device manufacturers to create products that worked on a wide range of computer platforms. Windows, UNIX, Linux and CP/M-based computers could often use their 9-pin outlets to connect to the outside world using the same brand and model external modem.
Mouse and Joystick Controller
Computers with graphical user interfaces like Mac OS, GEM or Windows PCs required new ways to interact with the user. Mice, trackballs and joysticks were sometimes connected to a PC through its 9-pin outlet. The Atari ST PC featured two 9-pin adapters to accommodate both a mouse and a joystick simultaneously. You may also find computers that have PS/2 or USB connectors for the mouse and additional 9-pin outlets for joysticks or dedicated game controllers.
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Ad Hoc Network and File Sharing
Before local-area networks or the Internet become widely used, the 9-pin outlet provided a way for your PC to sync or share files with another computer. This was done using a 9-pin outlet on one computer connected to another computer through a null modem: a special, RS-232 serial cable that enabled communication programs to transfer files and data back and forth just as they would using a real modem and phone line.
