Hi,
Here is the link to the document that describes the problem...
I have a dc7800 CMT and bought a WD Caviar 500 GB SATA III HDD and when I restarted the PC, I would consistently get a drive not found error.
I returned it thinking I got a bad HDD, and the new one did the same thing.
I also have an 8200 Elite CMT which runs SATA III drives at the SATA III speed.
It came with a SATA III Seagate 1 TB HDD
Since it came that way from the factory, I put it in the dc7800 and it has worked great ever since.
Now the reason I suggested the Intel 535 SSD is because I have an 8000 Elite CMT, and it is the same in every respect as the dc7900, except that it uses DDR3 memory (has the same chipset, etc).
SDH is not correct about the memory though. The dc7900 only supports DDR2 (PC2-6400) memory.
That does create quite a bottleneck between the memory and the processor, but there is nothing you can do about it.
http://www8.hp.com/h20195/v2/GetPDF.aspx/c04287292.pdf (see page 13).
I put a Sandisk Plus 240 GB SATA III SSD in the 8000 Elite PC (runs at the SATA II) speed, and it has worked just fine right from the get-go.
IMO, the Intel 535 is a better drive, but I got the Sandisk for only $40 bucks ($65 off, plus I had a $25 gift card), so I couldn't pass that up.
I have 3 HP business notebooks that I put the Intel 535's in.
That way, you can move your SATA III SSD to a newer PC that runs the drives at 6.0 GBPS, and not be stuck with a SATA II one running on a newer PC.
But like SDH wrote, there is some risk attendant in doing what I did.