| What do they do?
Universal Serial Bus (USB) is the latest way to connect external devices that don’t need particularly high-speed communications. Earlier ways included Apple Desktop Bus (ADB), which was primarily used to connect mice, keyboards and serial ports for external modems, printers, older scanners, and so on. USB is faster, more versatile, and can support a much wider range of devices, including mice, input tablets, keyboards, printers, scanners, hard disks, CD drives, and so on. You can also get adaptors to convert from USB to serial, parallel and even SCSI ports. How do they work?
Keyboards are merely an attractively presented array of labelled switches, turned on and off when you press the keys. Mice measure movement in two (x and y) directions, and signal the computer with that movement information. USB, ADB or serial devices contain a specialised chip to encode such information to an electrical form suitable for transmission along the cable. Each uses a simple (but different) type of cable, taking the signals to the port on the computer. There, another specialised chip decodes the signal back into the computer’s digital information, and passes it to the Mac OS. In this way, USB manages to move data at up to 12Mbits/sec, which is about the same speed as slow (‘10Base-T’) Ethernet networking, but slower than FireWire (up to 300 Mbits/sec) fast (‘100Base-T’) Ethernet connections, and SCSI. What can go wrong with them?
Most USB devices need software drivers, which can cause software conflicts. Many such devices draw power from the USB cable, so must be connected directly to the USB port on your Mac, or to a powered hub, which allows you to run more USB devices than you have ports on your computer. While USB devices can be connected and disconnected with your Mac running (as can most serial devices), ADB devices must not be ‘hot swapped’: if you try this, you risk zapping your motherboard with a voltage surge, and the resulting damage can require costly repairs. How can I upgrade them?
Apart from buying a better peripheral, most upgrades are in the software drivers. Apple provides support in the Mac OS, which is periodically updated on Apple support sites. Third-party drivers should be kept up to date to minimise compatibility problems. Further info
Web sites with further information include USB.org’s full FAQ, at www.usb.org/faq.html, and Apple’s USB home page, at www.apple.com/usb | |
