# Changing IDE to AHCI in BIOS after installing OS



## birrbert (Jan 9, 2010)

Hi everyone! 

I recently had to reinstall Ubuntu 10.04.1 LTS Server on my home server, but before that I loaded setup defaults in BIOS. By doing this the hard drive controller setting was made IDE. So I reinstalled the operating system in IDE mode and I was wondering if switching to AHCI would affect it? I know that Windows doesn't like if you do that and it will not boot. How would Ubuntu react? How would it affect the operating system and the system performance?

Thank you.


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## hal8000 (Dec 23, 2006)

Changing the IDE setting to AHCI will not affect your Ubuntu installation as the Ubuntu kernel has AHCI support, so will still boot.

Additionally, if your SATA or SATA II hard drive supports NCQ (Native Command Queuing) then you may see a small performance gain as NCQ allows SATA drives to accept more than one command at a time.

Linux NCQ (SATA native command queueing) support is enabled automatically, if your SATA drive supports it. At boot, you will see a line in dmesg (or kernel log) like this:

ata2.00: ATA-7, max UDMA/133, 321672960 sectors: LBA48 NCQ (depth 31/32)

If the line containing the sector count and maximum UDMA speed does not mention NCQ, your drive does not support it. 

You can search through /var/log/messages or just grep it like this:

dmesg | grep ata
dmesg | grep ATA

or just search for the NCQ commands:

dmesg | grep NCQ
dmesg | grep ncq


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## birrbert (Jan 9, 2010)

Thank you. In the meantime I had some problems with the home server's RAM module and I wasn't able to do tests on it, but I will resume my hobby soon.

Thanks again for the answer *hal8000*!


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