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Windows 7: How important is AHCI?

16 Nov 2010   #1
mendopaul

Windows 7 64 bit Home Premium
 
 
How important is AHCI?

I've just loaded Win 7 on a new machine with the OS on an Intel X-25 SSD and two other Sammsung T1's for storage. I didn't know to activate the AHCI capability when I did the install. Intel support is telling me that the only way now to get AHCI is to reinstall the OS after selecting AHCI in BIOS. How valuable or important is it to have the AHCI capability? Is this only for the SSD, or will it also work with the rotating hard drives. Thanks for your thoughts!


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16 Nov 2010   #2
smarteyeball

 
 

For optimal SSD performance, future firmware updates etc - it is important.

However Intel is incorrect about re-installation - AHCI can be enabled after the OS has already been installed in a different mode:

AHCI : Enable in Windows 7 / Vista

Your other drives will still function normally as well.
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16 Nov 2010   #3
fseal

Windows 7 x64 Ultimate
 
 

I switched to AHCI after OS install with no problems.

It will allow multiple threads to read/write to you drive "at the same time" whereas the IDE mode is only a single thread. This increases your read/write throughput DRAMATICALLY.
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16 Nov 2010   #4
xxxdannyxxx

Windows 7 Home Premium x64 SP1
 
 

I changed mine with the os installed using this tutorial

AHCI : Enable in Windows 7 / Vista
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17 Nov 2010   #5
joema

Windows 7 Home Premium 64 bit
 
 

I did some perf. tests with AHCI on and off, and couldn't tell any difference. That was about a year ago.

If you have a SATA optical drive, enabling AHCI may prevent it from working properly. This varies based on drive, firmware, motherboard and BIOS. More info:

LG optical drive won't burn DVD in AHCI mode
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17 Nov 2010   #6
pparks1

Windows 7 Ultimate x64
 
 

I ran for quite some time with my Intel X25-M G2 in IDE mode. There was an 8 second delay on boot from my gigabyte motherboard when I was in AHCI mode. I honestly felt that I didn't gain back enough in performance to compensate for the 8 second loss on each and every boot. I was unable to find any difference really between AHCI and IDE mode in all of the time tests and such that I did.

Later, Gigabyte released a new BIOS update which reduced that 8 second delay down to around 2 seconds...so at that point...I switched over the AHCI mode as it's better in theory.

But I wouldn't worry much if you are using IDE mode. It's unlikely to be a noticeable change.
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17 Nov 2010   #7
James Colbert

 
 

I successfully used the process linked to by earlier posters to enable AHCI in Vista (some time ago). I didn't really notice a significant performance gain, but the reason I enabled it was to gain Hot Swapping for my sata drives, which works like USB. Great for backing up partitions and the like for use as offline storage, restoring old files, working on ongoing projects that don't need to be constantly online, etc. As for Win7, AHCI was enabled when I installed. I believe hot swapping works for SSD as well (just not the boot drive...).

James
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17 Nov 2010   #8
FliGi7

XP / Win7 x64 Pro
 
 

So, if I have 4 sata drives (Win 7 OS, Win XP OS, Data, and Backup drive) and 2 sata optical drives with SATA currently set to IDE and I do the change in Windows 7 to make the Windows 7 drive AHCI, all of those other drives will still operate fine? I'm hesitant to make this change, given the possibility the optical drive may not function well and I believe I'd have to re-install my XP OS after this change, correct?
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17 Nov 2010   #9
James Colbert

 
 

Quote   Quote: Originally Posted by FliGi7 View Post
So, if I have 4 sata drives (Win 7 OS, Win XP OS, Data, and Backup drive) and 2 sata optical drives with SATA currently set to IDE and I do the change in Windows 7 to make the Windows 7 drive AHCI, all of those other drives will still operate fine? I'm hesitant to make this change, given the possibility the optical drive may not function well and I believe I'd have to re-install my XP OS after this change, correct?
That is correct. All of your drives will operate fine. No reason to worry at all. As to your question regarding XP, here is a google list of articles that should be informative:

AHCI xp - Google Search

James
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17 Nov 2010   #10
FliGi7

XP / Win7 x64 Pro
 
 

That was always a worry of mine in just flipping the switch on AHCI that I certainly could/should read up on but just haven't yet. Thanks for the info.
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 How important is AHCI?




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