PC 101
PATA - Parallel ATA, uses the 40 pin ribbon cable able to connect 2 ATA/IDE drives onto one channel. Only one drive can be active on the channel; So if one app needs something off one drive and another app needs something off the other drive, one app is going to have to wait for disk access. the ribbons are a mess to use unless you learn the art or origami. Ribbons also restrict the way of air flow in a case.
SATA - Serial ATA, uses a new 7 pin data cable in a slim package. Each drive is connected via it's own cable to it's own channel. All channels can be active at the same time. SATA cables are easy to manage and are much less restrictive to air flow
Bandwidth:
PATA 133mbs
SATA I - 150mbs
SATA II - 300mbs
SATA III - 6gbs