The graphic below compares the through-put for each of the Hard Drive buses used as a PC Hard drive interface to a Disk Drive. The speed of the transfer has increased from a through-put of 8.3MBps with ATA-1 to 150MBps with SATA-1. The throughput of the SATA II Hard Disk Drive [HDD] interface currently stands at 300Mbps.
Mother Boards are being produced which accept the Serial ATA bus and also
contain one or more PATA interfaces to accommodate legacy HDDs.
Use the older interface as a back-up drive or secondary drive, and purchase a new SATA drive to handle the Serial ATA interface.
Regardless of the Hard drive bus speed, the limiting factor has always
been the mechanical movement of the head and platter.
However as the bus speed increases as with SATA, the interface does see an increase because the data is off-loaded onto another IC, or to the Hard Disk Drive via the on-board cache.
Hard Drive Manufacturers page.
Solid State Drive Manufacturers page.
Hybrid Hard Drive Manufacturers page.
IDE Hard Drive Interface Bus page.
SATA Hard Drive Interface page.
or to the main PC Interface Bus page.
Use the Buses icon at the bottom of the page to reach the top level index for all bus types.
Editor note; I generated that graphic showing transfer speed back in 2005, but the data is still valid.
However the current maximum speed to a Hard Disk Drive [HDD] is 600MHz, or twice that shown in the graph.
But that new speed only counts if you have a hard drive with the newest interface, and a PC with the newest interface.
Otherwise the Disk Drive speed is what ever the cable interface is between the PC and the HDD.
In any case the transfer throughput relates to the PC to drive interface and not to how fast the drive spins at.
I think even in 2010 most drives only support the highest speed shown in the graphic.
Which reminds me, those are dates the specification(s) was written and not when products could be purchased.
The graph is also a nice little history reminder and speaks to how fast technology changes.