June 12, 2003

By Karen Kenworthy


It's finally happening! The North American Turtle Migration is underway.

Every year, at about this time, the great herd of box turtles moves from their winter range in the American southwest, to their summer grazing area in the Dakotas.

Though friendly once they get to know you, turtles are naturally shy. And they normally stay very close to the ground. That's why so few have of us seen the awesome sight of huge groups of turtles on the move.

But if you're patient, quiet and observant, you may see a few stragglers crossing a remote country road. Or you may find them resting in deep woods with running water, like those behind the secluded Power Tools workshop. What a treat!

Mass Transit

If you miss this show, don't despair. Fantastic journeys are taking place near you all the time. For example, enormous amounts of data flow in to, and out of, your computers ever day. Mice, microphones, modems, networks, keyboards, monitors, cameras, scanners and other devices contribute to this awesome traffic.

Since the earliest days, computers have used something called a "port" to talk to these external devices. No doubt the name was chosen because, just like sea ports, computer ports are where voyages begin and end. Instead of a ship, a special cable carries data from this port to an external device, and sometimes back again.

As you probably know, computer ports come in two popular flavors. One, often used to send data to printers, is called a "parallel port". That's because bits travel through this port eight abreast, using eight pairs of wire dedicated to that purpose. Other wires in the parallel port's cable deliver status information, such as whether the external device is ready to receive data, or out of paper.

The original parallel port specification was devised about 30 ago by a printer manufacturer called Centronics. Even though the company is now defunct, you may still hear printer ports called "Centronics ports", or connectors on the printer's end of a parallel cable called a "Centronics connector".

The other popular flavor is the "serial port". As its name implies, data travels through these ports one bit at a time, in single file. This type of port is often used to connect computers to modems and mice, though printers and other devices sometimes use this type of connection too.

Cables connected to serial ports usually have either 9 or 25 wires. One wire is set aside for outgoing data, and another wire is reserved for data traveling from the external device back the computer. Additional wires carry status information in various directions.

Serial ports are even older than parallel ports, dating way back to 1962. That's when an organization, called the Electronics Industry Association (now the Electronic Industries Alliance), or EIA, developed what they called RS-232 (Recommended Standard number 232). That's why you'll often hear serial ports called "RS-232 ports", and the cables connected to them called "RS-232 cables".

Now I've always liked the "RS-232" name. For me, it rolled off the tongue, was slightly melodious, while still sounding sufficiently pretentious. But sadly, the RS-232 moniker is now out-of-date, as old-fashioned as buggy whips or punched cards.

Over the years, the RS prefix was dropped in favor of EIA. Later, the American National Standards Institute (ANSI) and the Telecommunications Industry Association (TIA) adopted the standard. They also appended their acronyms to the standard's name.

Throw in a revision level and date, and you get the serial port standard's current name: ANSI/TIA/EIA-232-F-1997. Somehow it's just not the same. I guess I'm getting old. :(

Port Problems

Ports have served us well. But they are beginning to show their age too. For example, by today's standards, both types of ports are slow.

Parallel ports are the speedier of the two. The original parallel port could send up to 100,000 bytes per second. However, incoming data was limited to half that speed. Newer, "bidirectional" ports are equally efficient receiving data. They're faster too, moving up to 3 million bytes each second.

Parallel cables have other limitations too. Reliability degrades noticeably when the cables get much over 15 feet in length. And because their cables contain so many wires, they are expensive and bulky.

Serial ports are even more tortoise-like. Originally their top speed was a mere 11,500 bytes/second. Today, some advanced serial ports can double this top speed, moving data at a still pokey 23,000 bytes/second. Serial cables can be longer than parallel cables, sometimes over 100 feet in length. But they can be expensive too.

Both types of ports share another important limitation: a port can talk to only one external device at a time. Each external device connected to your computer required its own port.

Even today, computers are typically equipped with just one parallel port, and two serial ports. This was enough for a mouse, a modem, and a single printer. But if you needed more than three devices, you needed to expand your computer.

Fortunately, adapter cards that added two or more parallel ports to a PC were once readily available. And adapter cards providing four, eight, sixteen, or even more, additional serial ports were not uncommon.

But clearly, ports were getting out of control. Computers bristling with expensive and slow ports were not the answer to today's need for high- speed communication with lots of devices.

Bus Tour

The solution is something engineers call a "bus". Think of a bus as a digital version of the telephone party line. Party lines allowed several homes to share a single telephone line, taking turns making and receiving calls. Computer busses work the same way, allowing several devices to talk via a shared circuit.

Busses are as old as computers themselves. Pry open your computer's case, shake out the dust bunnies, and you'll see at least two busses. One allows the CPU and your computer's memory to communicate. Signals sent by the CPU to a particular memory location can be overheard by all other memory locations. Fortunately, memory locations are polite, and ignore data not addressed to them.

Another bus ties your computer's CPU and adapter cards together. This party line not only allows your CPU to communicate with each adapter card, it also allows adapter cards to talk to each other. The number of cards that can participate in this conversation is limited by the number of adapter card sockets your computer manufacturer decides to attach to your motherboard.

These two busses handle most communication within our computers. But what about external devices -- can busses help there too? The answer, increasingly, is yes.

For years, high-end computers have used something called a SCSI (Small Computer Systems Interface) bus to talk to fast disk drives, scanners and other devices. The original SCSI bus could connect up to seven devices, over a cable that carried eight bits in parallel. Data flowed at speeds of up to 5 million bytes/second.

The newest SCSI bus has improved that figure slightly, now carrying 320 million bytes per second. And rumor has it that a 640 million byte/second SCSI bus is already in development! Newer SCSI busses can connect more devices too, some as many as 15.

The SCSI bus is still popular in certain circles. But it has long suffered from high cost, and complexity. Configuring SCSI devices and busses can be a nightmare.

Today, two new busses have quickly taken over the computer world, becoming standard equipment on most new PCs.

One is often called "FireWire" or "iLink". But its proper name is "Institute of Electrical and Electronics Engineers standard 1394", or more concisely "IEEE-1394". Up to 63 external devices can be connected to this bus, communicating at speeds of up to 50 million bytes/second.

The IEEE-1394 is especially popular in the video industry. Digital cameras, especially digital camcorders, are among the devices often equipped with an IEEE-1394 connector. The bus's high speed allows two video sources to feed data to a single computer simultaneously, with enough capacity left over for the computer to send a separate feed to a recorder or monitor.

The IEEE-1394 bus was a tad expensive when it first came out. But recently the cost of IEEE-1394 circuitry has dropped a lot. Increasingly, the bus is standard equipment on new computers. You can also add a IEEE-1394 bus to older computers via an internal adapter card, or a card that fits in the PCMCIA slot of most laptops.

But by far, the most popular new bus is the Universal Serial Bus (USB). Today, it's found on almost all new computers. And it can easily be added to older computers via adapter or PCMCIA cards.

One USB bus can connect up to 127 devices to a computer. That's a good thing, because devices that use the USB bus include keyboards, mice, cameras, scanners, printers, modems, telephones, speakers, tape drives, external hard disk and CD drives, and almost every other popular PC peripheral.

The USB bus is fast, too. Originally limited to 1.5 million bytes/second, the new USB 2.0 standard pushes data along at 60 million bytes/second (480 million bits per second). That still falls short of the fastest SCSI bus, but then, USB is hundreds of dollars less expensive.

There's a lot more to say about busses and computers, including a new feature of my Computer Profiler. It now displays information about every USB device ever connected to your computer, revealing each device's type, manufacturer, and even internal serial number.

But those discussions will have to wait until our next get-together. However, you can get a sneak peek of the new Profiler now. Just visit the program's home page at:


As always, the program is free (for personal use). And programmer-types can download the program's free Visual Basic source code too!

Or if you prefer, get the latest version of every Power Tool, including the new Profiler, on CD. The disc also includes three bonus Power Tools, not available anywhere else. You'll find every back issue of my newsletter, and a few articles, in the CD's library. The CD even includes a special license that lets you use your Power Tools at work.

Best of all, buying a CD is the easiest way to support the web site and this newsletter. To find out more about the CD, visit:


And if you happen to cross paths with one of my turtle friends, take a moment to help them on their way. Move them gently, off the roadway, or away from other troublesome places. It's a long walk on such tiny little legs, and they can use all the help we can give them. :)

And if you see me on the 'net, or following the herd, be sure to wave and say "Hi!"

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