PC Hardware in a Nutshell, 3rd Edition

USB Characteristics

All USB devices share several general characteristics. Among these are:

Hot swapping

In theory, at least, USB peripherals can be connected to and disconnected from the bus at any time, without shutting down the computer or taking any action to inform applications or the OS that a device is being added or removed. In practice, this is not always the case, particularly with older interfaces and devices.

Warning

USB mass-storage devices are an exception worth noting. Disconnecting the USB cable before the drive finishes writing may corrupt data. If you use a USB hard drive, tape drive, or CD/DVD writer, read and follow the directions carefully to avoid losing data.

Automatic configuration

The USB host controller chipset installed on the PC motherboard or an add-on USB port card manages driver software and allocates bandwidth to each USB device attached to the bus. When a device is added or removed, the USB host controller automatically loads or unloads the driver for that device.

Tip

Educate your USB drivers. When you connect a USB peripheral to a root hub port or external hub, the USB driver “learns” that device/port combination. If you connect and disconnect USB devices frequently, you can make things faster and easier by allowing the PC to learn all combinations of device and port. Rather than simply connecting a device to a port and leaving it connected, plug that device in turn into each available USB port. That way, you can connect any device to any port ...