There's isn't really a particular BIOS option that selects between SATA 1.5 and 3.0, at least I haven't seen any yet.
Sata v2/3.0 Gbps is backwards compatible with Sata v1. It just drops down to Sata v1 spec if your board doesn't support it. Sata drives made attaching drives 'Plug-and-Forget'.
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