Like Ozeshin said, PAF's & P90's are chalk & cheese...
P90's are single coil pickups, commonly referred to as "soapbars" (because they resembled bars of soap). Prior to 1957, when the PAF's became the standard pickup, P90's were used in all Gibson electric guitars, and have been used in numerous models since then. It's a thinner sound than that of a humbucker, but fatter sounding than a Fender single coil because of the way it's made. Typical for a single coil, it tends to hum in the single pickup switch positions, but this generally stops when you select both pickups (the two pickups together cancel any hum).
A PAF is a humbucking pickup, like the name suggests, cancels any single coil hum (it "bucks" the hum) in the single pickup switch positions. Basically it has two coils, wound in oppsite directions to get a clear, hum free sound. Most humbuckers are more "powerful" than single coil pickups, and give a fatter sound. "Hot" PAF refers to pickups which were overwound, and subsequently gave a fatter, hotter signal. This in turn drove the front end of valve amps a bit harder, and mixed with power valve distortion, gave birth to the phenomenon we call "rock" music.
Most aftermarket pickups are "wax potted" to avoid any microphonics (squealing), though most PAF-a-likes are not, including the Gotoh mkII's and Seymour Duncan Seth Lovers.