The Universal Serial Bus

Ports are connectors provided on a computer to comunicate with
peripheral devices such as modems and printers. The RS232 serial
port introduced in 1969 could transfer data at a speed of 20
Kbps (kilobytes per second). The parallel port introduced in
1981 could transfer data at a speed of 150 Kbps. Later
improvements increased the speed of the parallel port to 4 Mbps
(megabits per second). Serial ports and parallel ports are
frequently subject to resource conflicts.

In 1996 the Universal Serial Bus (USB) was developed to replace
the serial and parallel ports. Today, the USB port is used to
connect scanners, digital cameras, and external storage devices
like CD-RW drives. USB 1.1 can transfer data at a speed of 12
Mbps. USB 2.0, introduced in 2000, can transfer data at a speed
of 480 Mbps.

Besides much higher speed, a main feature of USB is that you can
plug and unplug devices without restarting the computer. The
controller will sense the device and reconfigure. Installing a
USB device is as simple as plugging it into a USB port.

Another feature of USB is that a single controller can support
up to 127 devices simultaneously. A USB device can provide a
port for another device, allowing you to "daisy chain" devices
together, or you can use a stand alone hub. USB uses a single
IRQ, I/O address range, and DMA controller to poll the devices
for data.

The USB cable has four wires, two for communications, and two
that can provide up to 500 mA (milliamps) of power to the USB
devices. This means devices that only need a small amount of
power don't need to have a separate power supply and power cord.

As you can see from the above specifications, USB 2.0 is 40
times faster than USB 1.1. But most operating systems do not yet
have native support for USB 2.0. Microsoft has released USB 2.0
drivers for Windows XP. You can download them from the Windows
Update site: http://windowsupdate.microsoft.com.

You can plug a USB 2.0 device into a USB 1.1 port, but you will
only get the 12 Mbps transfer speed. Similarly, you can plug a
USB 1.1 device into a USB 2.0 port, but you will only get the 12
Mbps transfer speed.

If your computer was built in 1997 or later, you probably have
USB 1.1 support. The USB Implementers Forum provides a free
utility download that examines your hardware to determine its
USB capability. You can download it from:
http://www.usb.org/data/usbready.exe If you have a computer with
USB 1.1 support, you can use an expansion card that provides USB
2.0.

Manufacturers of USB 2.0 devices provide drivers that work with
Windows 98 or higher. First you insert a CD that comes with the
product to install the driver. Then, when you plug in the USB
cable, the port will automatically configure for the device.

The USB standard requires cables to operate at a length of up to
five meters, but many hardware manufacturers guarantee their
products to work only with the much shorter cable that they
provide.

By Stephen Bucaro