9. USB makes adding peripherals a
snap
By Mark Alberstat
Dear Mousepad:
I recently purchased a scanner for my Hewlett-Packard computer and it came
with a USB jack. Installation was so easy I was literally scanning in
minutes after hooking up the new hardware. It seems USB connections are
everywhere now. Just what are they, and how do they work?
Steven Malone,
Dartmouth
BACK IN THE dark ages of PC peripherals (that's anything more then three
years ago) attaching a scanner, joystick or some other piece of hardware
to your PC was an adventure.
You might not have the right drivers, there could be an internal conflict
that would take hours to troubleshoot, or maybe you would need an
expansion card installed before you could hook up your brand new $500
scanner.
Today, the world of peripherals is much different, thanks to a technology
called USB (universal serial bus). This nifty bit of hardware gadgetry was
developed in the late 1990s and has almost completely replaced devices
using the older and slower serial and parallel ports.
USB technology took off in 1998 when the iMac was released, showcasing how
easy it was to add peripherals to any computer. Today, most computers are
sold with four USB ports, two in the front for quick and easy access and
two in the rear for more permanent hookups.
Scanners, Zip drives, joysticks, digital cameras and a host of other
devices now use USB as their sole-source of PC-to-peripheral integration
and with good reason. It's fast, with data rates of 12 Mbps (mega-bits per
second).
For every USB system, there are two or three physical parts - the host
(usually the computer), a hub that can connect multiple devices and the
peripheral itself. Many times, a USB hub is not needed, as spare ports are
often available.
The connectors for USB are simplicity itself. With a one-size-fits-all
architecture, the chance of getting the wrong size or pin-out is zip.
One of the nicest features about USB is its expandability. You can have a
device plugged into a hub, which in turn is plugged into another hub,
which is then plugged into your host, and all devices on these hubs will
work just fine. The maximum number of devices on one chain is a
surprisingly high 127. That's a lot of scanners, mouses, keyboards and
joysticks.
Cable connections can also be as long as five metres, which can help
reduce the clutter on your computer table or workstation.
When you plug in a USB device, your host will usually put up a screen
telling you that it has detected new hardware. This bit of wizardry is
accomplished by the host sensing a voltage difference on its USB network.
It then asks the device for type, maker and bandwidth requirement. The
host assigns the new device a unique ID, so it can live peacefully with
other USB devices on the chain. Once the ID is settled, the operating
system loads the appropriate device driver and may ask the user for a
driver.
With an up-to-date operating system, the only thing the user needs to do
to add a new device to his or her computer is plug it in. It can't get
much simpler than that.
Another nice feature with USB is that it makes the idea of "plug and play"
a reality. The devices contain software and driver requirements, which
means you can plug in your USB scanner or other peripheral without
shutting off your computer. You can now add that digital photo of Fido you
just took to an e-mail by simply plugging in your digital camera,
downloading the image into your e-mail and sending it off. No fuss, no
muss, no rebooting and no hassle.
The Mousepad runs every two weeks. It's a service of Chebucto Community
Net, a community-owned Internet provider. If you have a question about
computing, e-mail us at mousepad@chebucto.ns.ca
Originally published 25 May 2003
