Various ports tell history of PC dialogue

MY OLD FRIEND Dudley is an accomplished lawyer, gourmet cook, world traveler, raconteur and an enthusiastic, if not technically oriented computer user.

He also tries to solve problems himself before he seeks help, so when he asks a question, I take it seriously.


"I'd appreciate it if someone would demystify the ports on a computer," he wrote recently. "Why the differences? What do the differences mean? How do you identify which types you have and what do you want for each type of add-on device? Why won't any port in a storm do?"

Did I mention that Dudley is given to bad puns?


Anyhow, it struck me that more than a few folks are confused by the sight of a dozen or more different connectors, slots and plugs on the backs of their computers - and the cable spaghetti that clutters their desktops when they start hooking things up.

Each of these "ports" on the back of a computer is in fact connected to a circuit designed to communicate with a particular device. Printers, keyboards, mice, monitors, scanners and other gadgets all handle electronic information differently, and at different speeds.

Over the years, the industry developed specialized connections for each device to maximize transfer speed at minimum cost with the technology available at the time. A keyboard, for example, doesn't require the speed or sophisticated circuitry it takes to drive a CD-writer.

Once a standard is set, inertia takes over. When all printer makers finally agree to use a certain type of connector, it's hard to change, even when something better comes along.

As a result, the ports on the back of your computer represent a working history book of computer technology. If you're confused or just curious, here's what you're likely to find back there:

Serial port - Known in the trade as RS-232C, the serial connection is the oldest "legacy" port on your computer (the industry's term for ancient technology). Its basic design dates to 1969, and typically, it shows up as a rectangular port with nine protruding pins.

The serial port was the first connector that allowed two-way communication between computers and other gadgets over long distances. Basically, it uses two wires - one to transmit and the other to receive. It gets its name from the fact that the digital ones and zeros that make up computer data have to move over the wire "serially," meaning one by one.

Lacking the sophistication of modern hardware, the standard serial port is limited to 115 kilobits per second. That's still OK for dialing up the Internet via an external modem, since phone lines can only move data at up to 56 kbps. But otherwise the serial port is too slow for anything useful. Most devices now take advantage of the faster USB connection.


Parallel port - The parallel port is a wide receptacle with 25 holes in two rows. It's commonly used for connecting a printer to a PC. Another legacy device, it was part of the original IBM PC in 1981 and was designed for high-speed communication that was largely one-way. Today's enhanced parallel ports can move data at 30 megabits per second, more than 200 times as fast as a serial port.

The parallel port gets its name from the way it handles information. Each byte of computer data (the equivalent of a single alphabetic character) consists of eight ones and zeros, known in the trade as "bits." The parallel port uses eight wires to send the bits simultaneously, so it's much faster than a standard serial port. The downside is that it doesn't work well over distances greater than 15 feet.

During the 1990s, hardware makers developed bi-directional parallel ports that could be used with scanners, tape drives, cameras, external CD-writers and other gadgets besides printers. Unfortunately, they were usually flaky, and the industry moved to the USB port and other high speed hardware for two-way data.

Today, many printers come with both USB and parallel port connections, and some laptop makers have eliminated parallel ports from their computers altogether. While the parallel port will probably linger on desktop computers for a few years, it's definitely on the way out.

Universal Serial Bus - The Universial Serial Bus, or USB, was developed in the mid-1990s to replace legacy ports with an all-purpose connector for printers, scanners, keyboards, mice, CD-writers, digital cameras, monitors, speakers, network adapters and other gadgets.

The USB port is a small slot about half an inch high and 1/8 -inch wide. You'll generally find at least two of them on desktop PCs and Macs. A single USB port can support multiple devices, usually through an inexpensive multiport adapter box called a hub.


With a speed of 12 megabits per second, USB ports will handle most low and medium-speed connectivity jobs - but look elsewhere to connect a high speed disk drive or digital video camera. USB 2.0, a second-generation scheme that promises to increase speed tenfold, is reaching the production stage, but few devices support it.

Keyboard and mouse - Keyboard and mouse ports are nearly identical - small, round 6-pin sockets located next to each other near one edge of the computer. They're known as PS/2 ports because IBM switched to this connector with its PS/2 line of computers in the late 1980s.

Newer keyboards and mice are often designed to use USB ports but I've found that the original ports work better. If you buy a USB mouse that comes with an adapter for the PS/2 port, use the adapter.

Video port - The standard VGA, or video port, consists of 15 pins in three rows. It connects your monitor to the computer's video display adapter. Normally, it's a standalone port - it won't have any close neighbors. But if you have a fancy video adapter with a TV tuner, you may also find a coaxial connector for your antenna or cable feed and RCA jacks for video and audio.

Music and games - Sound and game ports can be confusing because there are so many of them and they're close together. They're often unlabeled, other than by color or by icons so small you need a magnifying glass and a flashlight to see them.

Sound ports are small, round receptacles designed to connect your sound card to external devices with the miniature phone jacks used by the audio industry.


Most sound cards have at least three ports - an output to your speakers, an input for a microphone and an auxiliary output for headphones. Some contain an auxiliary input jack so that you can record from tape decks, boom boxes and other audio equipment. Better cards offer an optical output for digital speakers. While some companies have developed speakers that connect directly to a USB port, the standard audio connectors are cheap, work well and are likely to be around for a while.

Next to the sound connectors, you'll find a 15-pin game port - normally used for a joystick - and a legacy of technology that Atari developed in the 1980s. The joystick port can also be used to hook your computer to MIDI instruments such as electronic keyboards and drum pads. Although USB joysticks are available today, the game port's reliability and double-duty status are unlikely to make it obsolete.

Phone thingies - Most computers have at least two ports that look like phone jacks, and that's usually what they are. They're attached to your computer's internal modem. One connects your modem to a wall jack, and the other connects the modem to a phone so you can make calls when you're not online.

If you see what appears to be a third phone jack, a little bigger than the others, it's most likely an ethernet port, which connects your network adapter to a local area network or cable modem. You'll often find a tiny, blinking light next to a network port to indicate whether it's connected.

Firewire - Firewire is the name Apple gave its technology for ultra-high speed external connections, and the rest of the industry is rapidly adopting it under its catchy official title, IEEE-1394.

With speeds of up to 400 megabits per second -and twice that throughput on new, second-generation controllers - Firewire is fast enough for external hard drives and high-quality digital video (many digital camcorders have Firewire connectors).


Firewire ports, a bit smaller and squarer than USBs, are standard on all new Macs but only a few high-end Windows PCs. You'll see more of them on new PCs as time goes by.