Various ports tell history of PC dialogue

September 10, 2001|By Mike Himowitz

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.

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