Introduction
The USB 2.0 standard still remains a mystery to many users, but this is not for lack of trying to get the message across as to what, exactly, USB 2.0 is. USB 2.0 is the next step in building a more forward-thinking version of the USB technology. When the first version of USB was released to the public, high-speed devices that need the kind of bandwidth that USB 2.0 provides were little more than a dream. At that time, most high bandwidth applications were left for IEEE-1394 (Fire Wire) and it looked like it would remain that way until the introduction of USB 2.0.
If you look at the back of your computer you will see a few different communication ports. You will see a parallel port (printer port), an RS-232 serial port or two, probably even a USB port. The communication speeds of these ports vary from port to port. The parallel port or printer port in "Centronics" mode has a forward direction transfer rate of 150 kBps. The reverse direction data rate on the "Centronics" mode parallel port is one third of the forward rate, 50 kBps. Today's BIOS limits the RS-232 serial port to 38400bps. The USB ports on the back of most current systems have a maximum throughput of 12Mbps for full speed devices. None of these legacy ports are able to handle the high bandwidth peripherals of today.
Advantages of USB are that the USB controller takes one IRQ; none of the other devices require one. On USB devices, there are no jumpers to configure or hardware settings with which to fiddle. Configuration is very painless and simple. The utopia of plug-and-play operating systems will automatically (in most cases) install the device and drivers for you. USB uses conntector standards for all devices that leads to less confusion for the consumer. Think about all of the connections that are on the back of your typical PC. There is probably a PS2 mouse port, PS2 keyboard port, a nine-pin serial port (or two), a 25-pin printer port, and sound card ports (speaker out, line in, microphone in). That's a lot of ports to contend with, but what if all the devices used the same connector? If all of those devices where USB devices, you would be that much closer to the Legacy-Free dream system that Intel has been telling us about for the last couple of years.
USB supports multiple devices on the same port. The USB port will technically support up to 127 devices attached to it at one time. Of course, you will have to use some sort of USB hub to connect all of these devices. The USB bandwidth is shared between all devices on the channel. So, if some of your devices reserve a specific amount of bandwidth from the USB port, the amount of devices you can connect will be reduced. To get more bandwidth from USB, you would have to add additional USB ports, usually in the form of a PCI card. USB devices consist of, among other things, keyboards, mice, game controllers, cameras, storage devices, and scanners. If there is a device that you want for your PC, it is likely that is available as a USB device. With all of the devices currently available, especially the ones that require some bandwidth, the standard USB 1.1 specification just doesn't have the kind of "oomph" that it used to have.
