Correct. In fact, if you try this with an illegal A to A USB cable, you'll short the two power supplies together, possibly destroying one or both machines or causing a fire hazard. Even there were no danger to the machines from the problem with two power supplies, there still wouldn't be any way to get the two talking to each other, since USB doesn't support that particular kind of communication. A reasonably priced solution to handle this need is the USB bridge.

The acronym "USB" is short for the term Universal Serial Bus, a hardware interface that was developed so that peripheral devices like computer mice, keyboards, printers, digital cameras, scanners, PDA's and MP3 players can be easily connected to PCs. Computer manufacturers first began to replace serial and parallel ports with USB ports in 1997; today, every PC on the market contains at least 4 ports for USB connections.

Generally speaking, USB cable are classified into one of two different bandwidth groups: 1.1, which transfers data at a maximum rate of 1.5 Mbit per second, and 2.0, with a 480 Mbit per second data transfer rate. USB 2.0 is backward compatible with the lower data transmission requirements of 1.1, but the substitution can't be reversed; 1.1 just can't deliver the rate of data transfer that USB 2.0-rated devices need.