Problem

We have heard rumours that SATA II Hard drives are not backwards compatible with
SATA I controllers. This report is done to show that these rumours are actually incorrect and to clarify the details around the Serial ATA II Specification.

SATA Compatibility
Two features that qualify a HDD for 2nd generation SATA (or SATA II as is commonly
known) are NCQ and 3Gb/s transfer rate.

We tested the Seagate ST160812AS SATA II HDD and can confirm that it works on
SATA I enabled motherboards. We tested the Hard drive with the following motherboards…
GBT 8VM800M-775 – VIA VT8273R support SATA 150MB/s
Intel D865GBF – Intel ICH6 Support SATA 150MB/s
GBT 8I915GMF – Intel ICH6 Support SATA 150MB/s  

All our tests included the following…
1. Check for HDD during POST
2. Install OS All three main boards with SATA 150MB/s controllers passed.

Conclusion

The Seagate SATA II HDD’s are backwards compatible with SATA I specification.
Some Clarification on SATA II

Customers have been asking about the difference between SATA II 3Gb/s and SATA 3Gb/s. SATA II is not a specification but the name of the working group that has standardised the specifications for SATA 1.0, SATA 1.0a, SATA II and now SATA 2.5 specification They have now changed their name to the SATA-IO (Serial ATA International Organisation). 

The following article is taken from the SATA-IO website…
http://www.sata-io.org/namingguidelines.asp