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USB is a dream come true for PCs
technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology
Simple gray rule


USB is a dream come true for PCs


Technofile for Feb. 7, 1999

By Al Fasoldt

Copyright © 1998, The Syracuse Newspapers

Two and a half cheers for USB!

USB is a computer thing—the Universal Serial Bus. It's "universal" because it works on all kinds of computers (not just PCs) and can do all sorts of things. (It can handle your scanner, your mouse and your modem, for example.) It's "serial" because of the way stuff is sent back and forth, one piece of data at a time. (That's what serial means—one thing at a time.) And it's a "bus" because anything that carries a lot of other stuff around is known as a bus these days, both in real life and in the world of computers.

End of the nerd lesson for today. All you really need to know about USB is that it fixes a bunch of problems that have bedeviled PCs for nearly 20 years.

USB is a way of hooking things up to computers. Most PCs made over the last year or two have USB built in. If you bought a new PC lately, you can be sure it has USB. You'll need Windows 98 (or a later version of Windows 95) to make use of it, however.

If we talked about houses the way we talk about PCs, we'd say that all homes have a 120-volt bus. When you buy a toaster, you know it will connect to the power company's main electrical source without a problem. All you do it plug it into the "bus" connector on the wall. You don't have to shop for a parallel-port toaster or a serial-port toaster or a Mac toaster.

Nobody at the department store asks you if you need help plugging in the toaster. Nobody tells you to make sure you have the right plug or the proper cable. You just bring the toaster home and plug it in.

Computers aren't like that. PCs have serial connectors (a serial bus, where modems connect to the computer), parallel connectors (a parallel bus, where printers, scanners, cameras and even things like Zip drives connect), and other ways of connecting things. Macs, which don't work like PCs, have their own odd connectors and buses, too.

So if you buy a modem, for example, it probably will connect to your PC just fine, but it won't plug right into your neighbor's Mac. If you borrow a scanner when yours breaks, it might work with your PC and might not. It all depends on how it connects. If you want to use two different printers at the same time with your PC, you could be out of luck; most PCs have only one printer connection. Trying to use a scanner and a printer at the same time is a no-no, too, for most of us.

That's the most obvious problem with the way things connect to computers. But the most serious problem has to do with interrupts.

"Interrupts" mean just what you think. When your computer is humming along, the only way the printer or anything else connected to the computer can get attention is by interrupting the computer's main processor. It uses a "processor interrupt" (a separate pathway, so to speak) to do that. The computer can ignore this "interrupt request" (called an IRQ) or it can pay attention to it.

This sounds fine, except for a huge flaw in PCs. With only a couple of exceptions, everything plugged into a computer has to use a separate attention-getting pathway to the processor. (The CPU can't figure out what's going on if the printer and the modem are jumping up and down in front of each other, if you know what I mean.) Because of the dumb design PCs are stuck with, there aren't many separate pathways. There aren't many IRQs.

And that means you can only hook up a few things to your PC and get them to work all at the same time. Add something else and it might end up stealing an IRQ from something that needs it.

USB solves this dumb-as-nails problem by using only one IRQ for everything that's hooked up to the USB bus. You can plug dozens of things into the computer without running into a problem. Scanners with USB connectors are easy to find already, and you can even get a USB Zip drive.

You can also get a USB keyboard and a USB mouse. But don't. Windows doesn't make use of your PC's USB bus until it's up and running, so USB keyboards and mice won't work without Windows. And that means they won't work during bootup—which is when you NEED them to work if there's a problem. No doubt PC makers will get this little oddity fixed before long, and then we'll be able to give it three cheers. Until then, keep a normal mouse a regular keyboard handy if you use USB versions.


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