Like FireWire and USB, Serial ATA permits hot-pluggability, but other factors make it unsuitable for connecting external devices. Parallel ATA, as a specification, is more than a decade old, and the technology is running out of steam. The culprit is signal noise, said Spencer Roberts, senior manager of worldwide product marketing at Maxtor, a drive manufacturer that's part of the Serial ATA Working Group. As you raise the frequency of data moving down the wires, interference from neighboring wires blurs the electrical signal. ATA's current five-volt power requirement also contributes to interference, he said.
Lower voltage is less likely to create signal noise.
A serial interface can use lower voltage and fewer wires for signals to leak from. Another goal is to maintain software compatibility with existing ATA standards. So far, Serial ATA has been successfully supported on Red Hat Linux, Windows98 SE and Windows 2000. Likewise, you should be able to connect Serial ATA drives to an older parallel ATA bus. Thanks to the register-level compatibility, the adapter need only translate the serial ATA signals to parallel signals or vice versa.