Why sata is faster than pata

1) The interface has a higher theoretical bandwidth. SATA III is specced at 6 gigabits (not bytes) per second, while IDE is specced at a max of 167, and most IDE hardware is nowhere near that. Please note that these speeds are almost never attained in real life, due to overhead, inefficiency, and the phase of the moon.

2) Manufacturers concentrate their bleeding-edge development on the newer SATA interface, not the older IDE interface. So the new product development is happening on the SATA side.

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Edit: Or did you mean why is the theoretical speed for SATA higher than for PATA? One of my favorite topics, so let me know if that's what you wanted.