Usb connections move data at up to 12 mbps, about 100 times faster than a typical serial port, and over 4 times faster than the speediest parallel port. A USB mouse or keyboard wonÆt work any faster than its PS/2 or serial equivalent, but demanding devices like printers and scanners can deliver substantially faster performance.

Because USB devices can be linked, or daisy-chained, a single USB port can accommodate up to 127 devices. In practice, you could probably link only half that numberùbut thatÆs still more than youÆd ever need. All devices attached to a USB port run off a single IRQ, avoiding one of the PCÆs most formidable barriers to supporting multiple devices.

The two USB ports on the back of your PCùand any others on the caseùare part of a single USB hub. Every device directly connected or daisy-chained to either port shares the 12-mbps bandwidth. If you need more bandwidth for running multiple data-hungry devices like high-end scanners and printers, you must add a second USB hub (see the Upgrader article in the September PC World for basic instructions on how to install a USB hub and a PCI to USB adapter). Getting on Board

A smoothly functioning USB port has three prerequisites: a PC motherboard equipped with the proper hardware and BIOS; an appropriate version of Windows; and a power supply that can accommodate all the peripherals attached through the port.

If you purchased your PC within the last two years, the hardware and BIOS should be no problem. But having a couple of USB ports on your PC is no guarantee that theyÆll work properly. To see if your PC is USB-ready, download and run the free usbready.exe utility from the USB.org Web site at www.usb.org/data/usbready.exe, or you can get it from our cover CD. This program looks at your hardware, installed drivers, and Windows version and tells you what you need to run USB successfully.