Question: If a Harddrive is connected to an iMac's motherboard with sata connection, how can data be copied to or from the main hard drive faster the sata speed, even if it IS going through a thunderbolt port?
The quick answer Tom is that it can't. whenever you're considering a transfer of data between local devices on a computer, or multiple computers on a network, the speed of that transfer will be limited by the slowest connection in the chain. I suppose a "weakest link in the chain" metaphor could be used here.
SATA, depending on the flavor you're using has a theoretical maximum speed of 1500, 3000 or 6000Mbps. Those translate into 187.5, 375 and 750 MBps. As long as you're using a SATA interface, you will never achieve read or write speeds above those thresholds, regardless of whether or not you have a device in the transfer chain hooked up using Thunderbolt.
Of course, with that said, you'll never achieve anything near those thresholds either, because those are theoretical maximums which disregard other factors like hard drive speed and bus communication over head etc...
So in terms of speed, (nothing else), Apple may as well have just put an esata connection on the back of the iMacs right? I understand peripherals etc, but even with an 15 SSD drive RAID all its going to do is go the Sata max speed, because the internal hard drive is connected to the motherboard with Sata?
Speaking strictly of situations where you're interfacing with the internal SATA hard drive yes, that is where your bottleneck will be.
But Thunderbolt also has the advantage of being daisy-chainable, (I don't think that's word!) and, technically speaking, eSATA even in it's newest incarnation tops out at a theoretical maximum of 6Gbps and Thunderbolt comes in at 10Gbps. Again, these aren't actual achievable speeds, but the theoretical maximum works for comparison.
Thunderbolt is supposed to be about more than just storage. You could theoretically hook up your TB storage and then daisy-chain a display into that, for instance. Then, some of the "excess" would be used for that screen. You could have two storages connected to one TB buss and getting data from two separate SATA busses, filling the pipe a bit more. The idea was basically "let's make the pipe real big because we'll find some way to fill it eventually". With any data transfer right now, the storage device itself will usually be the bottleneck anyways, not its interface.
These are all just words on a screen, as Thunderbolt-equipped hardware is very thin on the ground right now. It looked awesome in the brochure, though. Time will tell how successful the interface really is, but the possibilities are there.
Incidentally I guess Thunderbolt is the thing which essentially made the iMac professional- especially in December when Sonnet are releasing a thunderbolt- express card adapter. Then all you need to do is add an express card hub and buy a whole bunch of IO adapters (not cheap) and you almost have a Mac Pro, minus some of the processing power and upgradeability.... :D