The early days of computing are discussed elsewhere on this website, since they have a lot to do with where SATA came from. Early theory said that parallel buses (in which data was sent a byte at a time, and later at two bytes at a time) must be faster than serial buses because in a serial bus the data moves a bit at a time. Two bytes is sixteen bits plus two check bits; sending sixteen bits at one time must be faster than sending one bit at a time – yes?
In fact, no. Or not at the time, because when IBM introduced the IBM AT (with AT standing for Advanced Technology), it came with a serial bus and the data transfer was the fastest anyone had seen at that time. And serial buses brought other advantages – they were cheaper to make because they used seven conductors instead of either 40 or 80. That also meant that cable sizes became smaller, which was a huge plus in an industry always striving for size reduction. Hot swapping – the ability to replace one component with another without having to reboot the system – was another major advantage, though defects in various operating systems sometimes negated it.
Amazing as this must seem now to anyone under the age of 40, the IBM AT was the first microcomputer in which the hard disk was a central part of the configuration. The interface through which data transfer to and from the hard disk was carried out was eagerly seized on by other manufacturers who made it an industry standard. IBM didn’t mind that, since it meant more people making devices that could be plugged into (were “plug-compatible” with) an IBM machine and THAT meant more people buying IBM.
And so the technical superiority of the IBM AT made SATA the de facto standard bus.