USB: Universally Altering Your Peripherals - Serial, Huh?
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You may have noticed that USB stands for Universal Serial Bus. But didn't we dump serial in the glory days of the "Trash80?" In short, Yes-we did, for something called "parallel." In case you are wondering what the differences are, here's a quick rundown. (If you've never opened a computer before, don't worry. If you've ever bought a computer, you've probably heard most of these terms before.)
Parallel communication is taking a block of information, cutting it into parts, and sending them all along at once together. A lot of the devices in your computer communicate this way: your floppy drive, printer port, Parallel ATA hard drives, ATAPI (CD, DVD etc), and anything hooked to the "PCI" bus through those white slots internally on the motherboard.
These devices all have varying "widths" or amount of parallelism. The PCI bus, for example, is 32 bits wide, which means that at any one time, it sends blocks of 32 bits together. The ATA one, normally attached to your hard drive, is 40 bits wide. This was an advantage over other serial methods at the time, such as RS-232, because at the same speed you could send much more data.
Serial communication is of course just the same as parallel, only instead of multiple bits you send only one at a time down the wire. Makes sense that parallel would be much better right?
To a point.
The problem with having multiple wires all close to one another is that the proximity causes interference. That's why your older ATA-33 cables no longer work at the ATA-100 and higher speeds that hard drives are capable of communicating at. They went from 40 wires, each one carrying information, to 80, which put a ground wire between each "sending" wire to try and reduce the interference. At high speeds it's very difficult to have all those wires stay synchronized, and not confuse the receiver at the other end. There are also issues with how long the cables can be without adding "repeaters" to strengthen the signal.
This is why "High Speed Serial" has started to make a comeback in the last few years. We first saw this with the arrival in 1995 of USB, and it continues today with the integration of Serial ATA, PCI Express, Ethernet, and other similar standards. The difference that 20 years makes is this: even by sending one bit at a time, you can achieve much higher data rates now, with a much more simplified interface. Not only are the materials better to keep signal integrity up, but the methods for "handshaking," error detection and correction, and simply the speed that both transmitter and receiver are capable of working at have improved tremendously.
Next: The Standard Itself >>
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