Upgrading: SATA Or UltraATA?
Once the decision in favor of a hard drive upgrade has been made, the first order of business is deciding on the interface. Practically all currently-available drives can be found in UltraATA/100 (or /133) and SATA versions. SATA, being the most modern interface, offers a theoretical peak transfer of 150 MB/s (SATA I) or 300 MB/s (SATA II).
Additionally, SATA II also supports hot-plugging, which was not included in the previous version of the SATA standard. It also includes staggered spin-up of several drives, easing the burden on weaker power supplies by delaying the power draw of the drives as they spin up.
However, the higher bandwidth of the SATA II interface offers practically no measurable improvements in real world applications at the moment, as the magnetic medium is the limiting factor. The real advantage of SATA II lies in its support of native command queuing (NCQ). This feature allows the hard drive's logic to reorder incoming commands if possible, allowing the drive to answer them in an optimized sequence. The aim is to reduce the movement of the read/write heads to a minimum, allowing the drive to spend more time reading and writing data.
Another much more general advantage of SATA drives is their much simpler wiring. Unlike the unwieldy and delicate ribbon cables of the (Ultra)ATA interface, SATA cables require only seven wires, can be up to one meter long and are much less delicate.
As far as performance is concerned, even the UltraATA/100 interface doesn't hold back even the most recent drives. On the other hand, each device should still be attached to its own controller channel, as sharing a channel between two devices also means sharing the channel's overall bandwidth.
UltraATA drives are still a little cheaper than the SATA versions, which may be a large factor for upgraders. However, if you're planning a bigger system upgrade involving several components, we would always recommend choosing the SATA drive. In any case, always use the newest drive in your machine for your operating system, as it is most likely faster than your previous model. Also, consider a fresh, clean installation of the OS as well, as this usually yields a subjective performance boost - especially if your drive and OS installation are already two or more years old.