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MarkW

New drive setup - ACHI ?

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Just about to build my computer and was reading through the MB manual regarding installing windows. I have two Cavair Black drives, one for the OS, one for FSX and I would like to know if I need to enable ACHI or IDE for these drives ? I will not be running a RAID setup. thanks,Mark.

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AHCI is ideal for maximum transfer rates and reduced seek times for *any* SATA HD which supports it. It is not only for SSDs.

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AHCI is ideal for maximum transfer rates and reduced seek times for *any* SATA HD which supports it. It is not only for SSDs.
You are right and I stand corrected, I should have specified. :P

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I believe the Asus P8P67 PRO (B3) MB is preset in the bios to ACHI enabled. So I was assuming that they are recommending, regardless of drive type. Correct?

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AHCI is ideal for maximum transfer rates and reduced seek times for *any* SATA HD which supports it. It is not only for SSDs.
Most of the literature I've read on this says that on traditional platter drives, AHCI only provides a performance advantage in a heavy random disk access (e.g. network server) environment where command queuing can effectively reorder disk head seeks that would otherwise keep the head thrashing all across the drive...in a typical desktop PC, AHCI is usually just a tad slower than IDE (but not much). On an SSD, AHCI's Native Command Queuing can really speed up SSD I/O by allowing the PC to stack up I/O commands--the advantage isn't due to being able to optimize disk head movement (since there are no disk heads in an SSD), but instead the CPU does not have to wait for each disk I/O command to complete before issuing the next one. So the SSD can immediately get to work on the next I/O command in the queue when it completes an I/O command, rather than having to sit idle waiting for the CPU to then issue the next command after the disk subsystem signals that the last command was completed.All that said, I would build the PC with AHCI enabled in the BIOS, because that way when Windows is first loaded it will install the AHCI drivers, along with the IDE drivers (which are always installed by default). Once that's done, you can then later switch back-and-forth between AHCI and IDE mode at will to determine if there's any difference in performance that matters to you, or if you later add an SSD and need AHCI. If the OS isn't first installed with AHCI enabled, the AHCI drivers are not installed, and switching later to AHCI becomes a much trickier proposition.

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In the end I just installed Windows 7 at the default IDE settings although I see that ACHI drivers are installed so I am guessing that it has been enabled in the bios.Mark.

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Most of the literature I've read on this says that on traditional platter drives, AHCI only provides a performance advantage in a heavy random disk access (e.g. network server) environment where command queuing can effectively reorder disk head seeks that would otherwise keep the head thrashing all across the drive...in a typical desktop PC, AHCI is usually just a tad slower than IDE (but not much). On an SSD, AHCI's Native Command Queuing can really speed up SSD I/O by allowing the PC to stack up I/O commands--the advantage isn't due to being able to optimize disk head movement (since there are no disk heads in an SSD), but instead the CPU does not have to wait for each disk I/O command to complete before issuing the next one. So the SSD can immediately get to work on the next I/O command in the queue when it completes an I/O command, rather than having to sit idle waiting for the CPU to then issue the next command after the disk subsystem signals that the last command was completed.All that said, I would build the PC with AHCI enabled in the BIOS, because that way when Windows is first loaded it will install the AHCI drivers, along with the IDE drivers (which are always installed by default). Once that's done, you can then later switch back-and-forth between AHCI and IDE mode at will to determine if there's any difference in performance that matters to you, or if you later add an SSD and need AHCI. If the OS isn't first installed with AHCI enabled, the AHCI drivers are not installed, and switching later to AHCI becomes a much trickier proposition.
I've never really noticed a difference with mechanical drives either way, but as you said it is ideal to at least select AHCI from the beginning and then one can switch back should they so choose.

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You can switch to IDE in BIOS if you originally installed with AHCI?Thats good to know.....any known ill effects?

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You can switch to IDE in BIOS if you originally installed with AHCI?Thats good to know.....any known ill effects?
You may need to edit a registry key to tell Windows to load the generic IDE driver rather than the AHCI driver in order for the machine not to BSOD with an 0x0000007b (or similar) stop code. Microsoft has a Knowledge Base article on the matter.

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You may need to edit a registry key to tell Windows to load the generic IDE driver rather than the AHCI driver in order for the machine not to BSOD with an 0x0000007b (or similar) stop code. Microsoft has a Knowledge Base article on the matter.
No, it's the other way around...the reg key edit will be required if the SATA mode is changed *to* AHCI mode and the AHCI driver is not enabled. The IDE driver pciide.sys is always enabled when Windows is installed, regardless of the actual presence of a device running in IDE mode. The AHCI driver msahci.sys, is only enabled at the time of Windows installation if one of more of the active drives is running in AHCI mode.At any rate, the registry edit in the referenced KB article only covers enabling the AHCI driver, and does not affect the IDE driver.@gjharrall--no ill effect...you'll probably have to double-boot the machine once after you switch modes, as Windows will recognize the devices running in a new (changed) mode, load the IDE drivers, and then need to reboot again. The data structures etc are all the same, and high-level programs will not see a diffference--it's just a difference in the low-level (OS) driver protocols.

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Thanks!Is it really worth switching to IDE from AHCI for FSX purposes?

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Thanks!Is it really worth switching to IDE from AHCI for FSX purposes?
Probably not, unless you have an older storage device that doesn't play well with AHCI and runs significantly slower as a result. IIRC, some of the older 150GB Raptors had issues with AHCI, at least with earlier versions of the drivers. But newer drivers, and especially newer devices, shouldn't have those kinds of problems.

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Don't know if i've done the right thing or not but i just finished upgrading my rig to a SANDY system and did a clean install of W7, formatted my fsx drive and left the default AHCI enabled in my bios.Both my drives are WD-CB-1T-7200rpm.

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No, it's the other way around...the reg key edit will be required if the SATA mode is changed *to* AHCI mode and the AHCI driver is not enabled. The IDE driver pciide.sys is always enabled when Windows is installed, regardless of the actual presence of a device running in IDE mode. The AHCI driver msahci.sys, is only enabled at the time of Windows installation if one of more of the active drives is running in AHCI mode.At any rate, the registry edit in the referenced KB article only covers enabling the AHCI driver, and does not affect the IDE driver.
Perhaps that's the way it's meant to function, but in practice the effect is often the same. In my job as a PC technician (at a serious repair shop, you know, one actually interested in repairing PCs rather than selling you a replacement with a warranty) I have seen it many times when working on modern PCs that have Windows installed on a SATA drive which is configured to run in AHCI mode. Our HD diagnostic tool (MHDD) doesn't recognize drives set to function in this mode, so we have to go into the BIOS and change the SATA mode to IDE (or whatever the manufacturer has decided to call non-AHCI mode). Occasionally I'll forget to change the setting back to AHCI and on boot will get a nice 7b stop code. It works both ways, if you change to AHCI when the system was already configured to run in IDE mode, Windows will likely not boot. On Vista or 7 systems the startup repair utility can *usually* fix this.

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