Just Curious - AHCI Mode and IDE Mode?

[neo668]

I have an SSD and a HDD. So I set my computer to AHCI mode and installed Win 7 on both the SSD and HDD - the latter to service the SSD if necessary, like updating the SSD firmware. So both Win 7's were installed in AHCI mode.

Yesterday, my mobo BIOS had a problem and I couldn't get into it after clearing CMOS and resetting it. But if I bypass the BIOS the computer is able to boot normally. The BIOS defaults to IDE mode after a reset. I couldn't get into the BIOS again to set it back to AHCI mode and so I couldn't boot to the SSD which is my main OS drive. I then unplugged the SSD from the mobo and booted again, which means to Win 7 on the HDD.

To my surprise I could get into Win 7 on the HDD. Why is this? It was installed in AHCI mode just like the SSD and the mobo had defaulted to IDE.

I'm just curious and would like to know how this is possible.

Thanks.

 

[johan851]

The IDE driver is a much more basic driver. My guess is that Windows didn't have any trouble recognizing the drive and booting to it despite being configured for AHCI.

 

[neo668]

Thanks Johan.

I'm just perplexed that it would not boot to my SSD while it had no problem booting to the HDD. Both had Win 7 installed the same way, ie. under AHCI.

 

[johan851]

No idea. But it's not worth worrying about, since you don't want IDE mode anyway.

 

[neo668]

Yep. I'm not worried. I'm just curious.

Anyway it's good to have an OS that will boot under any situation.

 

[I.M.O.G.]

Depending on the mobo, it may recover settings after a reset. If I reset cmos on one of my asus boards, it will go back to default settings and prompt me to enter bios and recover settings the next time I start it up. If I then hit reset without going into bios, it will try to boot again at my previously overclocked/configured settings.

Boards behave differently depending on model. I'm not sure what is normal for your GD55, but when you booted again after not going into BIOS, it may have reverted to your previous settings from before you hit the reset button.

 

[neo668]

The problem I had with my MSI board was that, after a BIOS update and I tried to get into the BIOS to set up everything again the system would freeze. I couldn't set up the BIOS again and it does not automatically go back to the previous settings, unlike an Asus.

I eventually was able to downgrade the BIOS with a bootable USB stick, clear the CMOS and get back into the BIOS again. I was really lucky.

Before downgrading, and if I just bypassed the BIOS setup and booted the computer I could get to the Win 7 on the HDD but not to the SSD.

I don't have a problem now but just wondered why the HDD could boot under IDE and not the SSD. Maybe the SSD is more sensitive to the AHCI/IDE differentiation.

 

[I.M.O.G.]

Ya, I understand your problem... Was just thinking the board may act like mine as that might explain it, but I guess that isn't the case. I haven't ever seen an OS be bootable when AHCI/IDE is set incorrectly in bios... We do a lot of drive swapping and OS installs for benchmarking. Its definitely a curious thing that happened there.

 

[c627627]

To clarify for others reading this: Without editing the registry, you cannot go from IDE to AHCI if you haven't originally installed Windows under AHCI.


But you can go from AHCI to IDE without a problem.

 

[neo668]

But you can go from AHCI to IDE without a problem.

This explains it. Thank you.

This, however, appears to be true for the HDD and not the SSD. I can never boot into the SSD if the mobo is set to IDE. But SSDs are such fickle creatures.

 

[c627627]

I installed both Windows 7 and WIndows XP under IDE, not AHCI as I should have. I then edited the registry to switch to AHCI.

Going from AHCI to IDE is possible for me even with SSD, for what it's worth.


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