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Is it somehow possible to use AHCI on Windows if the BIOS does not have the option to enable it? This is a known problem especially on mid-old Laptops that have chipsets and drives that perfectly support SATA and AHCI, but only provide the legacy IDE mode in BIOS. Especially with SSD's this can often be a problem.

I know that Linux has no problems to run everything in SATA and AHCI mode on these machines.

So, is there any possibility to also make Windows "override" the BIOS?

Some kind of alternative BIOS's, drivers, etc? Or some kind of Linux-based boot module that emulates an AHCI-capable BIOS to Windows while booting up?

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So you're saying Linux is able to successfully override the legacy IDE mode set in the BIOS? – Karan Dec 16 '12 at 15:47
I have a laptop running Windows 7 and it runs the HDD on legacy IDE mode (because the BIOS has no option to turn AHCI on). But if I boot from, for example, a Knoppix live distribution, it runs the HDD in SATA mode. So, i assumed that Linux is ignoring the BIOS and somehow checks itself what hardware is really in there (I mean, coreboot can do this, too, and thats also a Linux - but I don't want to flash coreboot on a Laptop from which I don't know if it will work. That's why I asked if there's some post-BIOS way). – Foo Bar Dec 16 '12 at 16:47
I also found this site: saying that Linux ignores the BIOS after it is loaded. I was hoping that's somehow possible on Windows, too. – Foo Bar Dec 16 '12 at 16:53
Yes, that site says "Once loaded, Linux ignores the BIOS - it has its own disk access procedures which are capable of handling huge disks.", but it's not talking about IDE vs. SATA mode. Anyway, you might be correct because I don't have an old system like this to confirm. In any case I do not recommend any loader, for stability reasons as well as there being no guarantee it will allow Trim commands to be sent to the SSD while in emulated AHCI mode. If you're up to it the specific laptop model might have a modded BIOS available that enables the otherwise hidden option. – Karan Dec 16 '12 at 17:14
I already searched a lot, there's no modded BIOS available. I'm currently fiddling around with a BIOS modding tool (MMTOOL) and Option ROMs to get it working. The thing is that I don't know how to add menu points to the BIOS "GUI". An available Option ROM alone does not do anything if I have no option to enable it in the BIOS setup menu. – Foo Bar Dec 16 '12 at 18:41

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