The Universal Serial Bus (USB) was designed by a consortium of hardware and software vendors—Compaq, Intel, Microsoft and NEC—beginning in 1994. It was conceived to provide a standardized way of connecting a wide range of peripheral devices to a computer (read “personal computer”) and to correct some of the limitations of traditional serial and parallel lines.
USB has the following advantages:
Up to 127 devices can be connected.
Devices can be added and removed while the system is running.
Connectors have been standardized across all device types.
It is much faster. The theoretical bandwidth of a USB bus is 12 Mbs/sec; however, actual throughput is more like 8-8.5 Mbs/sec, and devices seldom achieve more than about 2 Mbs/sec.
USB cables contain only four wires: power, ground, send, and receive. Communication is handled in a hierarchical manner, under the control of a master; attached devices all function as slaves, thereby eliminating issues such as avoiding collisions. USB cable connectors are illustrated on the far left in Figure 12-2, and Figure 12-5 illustrates their corresponding pinouts.
Figure 12-5. USB connectors
B-type connectors are used for the USB port on the device, and A-type connectors are used for the port on the hub or computer system.
FreeBSD, HP-UX, Linux, Solaris, and Tru64 all support USB devices to some extent, although the support under HP-UX and Tru64 ...