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From: Dave <freebsd01@dgmm.net>
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Subject: Re: The other problem : AHCI unbootable
Date: Sat, 25 Jun 2016 13:10:36 +0100
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On Saturday 25 June 2016 04:56:39 Manish Jain wrote:
> While installing FreeBSD 10.3 amd64, I tried switching from IDE to AHCI 
> in my BIOS's boot configuration. But when I do this, the installer 
> installs the OS on the hard disk, and then the system is unbootable - 
> the BIOS screen hangs with the message : boot record missing.
> 
> Can anyone please tell me what might be the problem ?
> 
Not sure exactly what you are saying your process is, but switching between AHCI and IDE without a full and clean install will cause you problems.  Solution.  Don't do it.

This advice applies at least to WinXP too.  That tends to reboot while the Windows logo is on screen no matter which way around you do it. ie if you install in IDE mode it will reboot if change to AHCI mode.  Same happens if you install in AHCI mode and then try to boot in IDE mode.