The conventional serial ports used on PCs have been around since the earliest PCs; they
have changed a little, but not much. While functional, they have serious limitations in
terms of expandability, software support and performance. In the mid-1990s, a consortium
of PC and telecommunications industry giants--including Compaq, IBM, Intel, Microsoft, NEC
and Nortel Networks (then Northern Telecom) developed a new interface standard for
attaching relatively low-speed devices to the PC. This interface is called the Universal
Serial Bus or USB. While USB support started being supported in many PCs
many years ago, it has only recently started to gain widespread acceptance. All new PCs
are now equipped with USB support, and USB ports can also be added to many older systems
as well.
The USB interface is specifically designed to allow easy connection of a wide variety
of devices; it is intended to be user-friendly and truly "plug and play". On a
system equipped with USB, one can "hot swap" devices, meaning they can be
plugged into the system or removed without needing to power the system down or doing
anything to it before the change is made. Up to 127 devices are supported, and multiple
devices can easily be added to a single PC by chaining them together using hubs. The USB
connection is of course serial, and the current version (1.1) runs with a maximum
throughput of 12 Mbits/second (1.5 Mbytes/second), which is shared by all devices. There
is also a slower-speed, 187.5 kbytes/second mode available for very slow devices, such as
keyboards.
USB's initial acceptance was relatively slow in coming, but once it got going, the
variety of USB devices that appeared on the market surprised many people, probably
including its developers. The flexibility and expandability of the interface, and the ease
with which devices could be attached, made it very attractive to many users. Many of the
devices that were made available in the USB interface were never intended for USB when it
was first created. Most storage devices would certainly fall into this category.
Today, one can get a wide variety of storage units that use the USB interface. This
includes floppy disk drives, hard disks and optical drives. They work on the USB
interface, and certainly there is no issue with floppy disk drives for example. The
problem is that the maximum throughput of the interface is 1.5 MB/second--and that's a
theoretical maximum, meaning the reality is somewhat lower. This is fine for mice, modems
and scanners, but it's very slow for hard disks, considering that modern drives can have
throughput level 20 to 30 times above that number. Even something like a 40X CD-ROM
drive has a maximum throughput far above 1.5 MB/second. Of course, USB was never
envisioned as an interface for high-speed devices like hard disks, so its designers can't
be blamed for these limitations.
USB remains popular for hard disks and other storage devices for those who don't have
other options; however, in almost every case a higher-speed interface is a better idea if
that's at all possible. Otherwise, you will seriously restrict the performance of the
device. This is fine for some tasks, such as occasional backup, but far from ideal.
Responding to the faster devices that many companies began developing for USB, USB 2.0 was developed, with similar attributes but much faster
performance. IEEE-1394 is another high-speed serial
interface that competes for the same areas of the market.
Note: For more information
on USB, see the USB Implementers Forum site.
Next: IEEE-1394 (FireWire, i.Link)
