SATA II is the next generation of SATA hard drives, that can transfer data (with a SATA II compatible mobo) up to 300 MB/s. The regular SATA HDs transfer data at up to 150MB/s.
Im not 100% sure, but I think the SATA II HDs are backwards compatible. Make sure to get further input on the backward-compatibility, though.
Intel E6750...........PSN: ELBATROP
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Windows 7 Home Premium 64