Q1: How fast is USB?
A1: High speed USB products have a design data rate of 480 Mb/s. Full speed USB devices
signal at 12Mb/s, while low speed devices use a 1.5Mb/s subchannel.

Q2: How does this compare to other connections used with PCs and workstations?
A2: Here's a quick list of the maximum transfer rates for various connections in megabits (Mb) and megabytes (MB) per second:

serial port: 115kbits/s (.115Mbits/s)
standard parallel port: 115kBYTES/s (.115MBYTES/s)
Original USB: 12Mbits/s (1.5MBYTES/s)
ECP/EPP parallel port: 3MBYTES/s
IDE: 3.3-16.7MBYTES/s
SCSI-1: 5MBYTES/s
SCSI-2 (Fast SCSI, Fast Narrow SCSI): 10MBYTES/s
Fast Wide SCSI (Wide SCSI): 20MBYTES/s
Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow): 20MBYTES/s
UltraIDE: 33MBYTES/s
Wide Ultra SCSI (Fast Wide 20): 40MBYTES/s
Ultra2 SCSI: 40MBYTES/s
IEEE-1394: 100-400Mbits/s (12.5--50MBYTES/s)
Hi-Speed USB: 480Mbits/s
Wide Ultra2 SCSI: 80MBYTES/s
Ultra3 SCSI: 80MBYTES/s
Wide Ultra3 SCSI: 160MBYTES/s
FC-AL Fiber Channel: 100-400MBYTES/s

The fastest connection commonly found on PCs is UltraIDE, which is used for hard drives and CD-ROMs.

Q3: So which is faster, a USB peripheral or a serial/parallel/SCSI/1394/etc. one?
A3: This depends on what the peripheral is and how it's made. For example, a USB keyboard won't let you type any faster than a normal PS/2 keyboard because your typing speed is limited by how fast your fingers can hit the keys, not by the speed of the keyboard's connection to the PC. Similarly, devices like printers and scanners may be able to run faster on USB than they can with a standard parallel connection, but only if the print head or scan engine can keep up with USB's higher data rate, which is not necessarily the case. On the other hand, USB makes possible peripherals that were impractical with earlier connections, such as video cameras and ADSL and satellite modems.

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