风能车:有高手吗？能帮帮我翻译高难度的英文文章吗？谢谢！

A USB system consists of a root hub that plugs into the main bus (see Figure 2B-1). This hub has sockets for cables that can connect to I/O devices or to expansion hubs, to provide more sockets, so the topology of a USB system is a tree with its root at the root hub, inside the computer. The cables have different connectors on the hub end and on the device end, to prevent people from accidentally connecting two hub sockets together.
The cable consists of four wires: two for data, one for power (+5 volts), and one for ground. The signaling system transmits a 0 as a voltage transition and a 1 as the absence of a voltage transition, so long runs of 0s generate a regular pulse stream.
When a new I/O devices is plugged in, the root hub detects this event and interrupts the operating system. The operating system then queries the device to find out what it is and how much USB bandwidth it needs. If the operating system decides that there is enough bandwidth for the device, it assigns the new device a unique address (1 - 127) and downloads this address and other information to configuration registers inside the device. In this way, new devices can be added on-the-fly, without any user configuration required and without having to install new ISA or PCI cards. Uninitialized cards start out with address 0, so they can be addressed. To make the cabling simpler, many USB devices contain built-in hubs to accept additional USB devices. For example, a monitor might have two hub sockets to accommodate the left and right speakers.