It's easy - manufacturers go with the failsafe settings so that they have to deal with as few complaints as possible. It's not only disks - horrible default 60Hz refresh rate back in the days of CRT, etc.

If you are a power-user you will go through all the settings yourself in detail anyway. If you are a casual user, you won't probably mind (or recognize) slower performance.

Well I now have AHCI enabled on my machine.  It seems a bit faster.

Oh, I should mention that the registry edit yrag advised for me is for an AMD based machine.  The registry edit for an Intel based machine is as follows...

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV... then right click "Start" > change value from 1 to zero. 

And yes, the method advised by yrag [mentioned in #18] DOES work.  The only reason I had issues was because I was dual booting and yrag was either unaware or had forgotten this when he first gave me the registry edit.  Once the secondary OS was taken out of the equation yrag's advice worked as advertised/promised.

Something of interest....;)

http://expertester.wordpress.com/2008/07/24/ahci-vs-ide-%E2%80%93-benchmark-advantage/ 

The register key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci is for both Intel and AMD system...

The register key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV is related to the RAID mode... standard RAID mode are 0-1-2-3-4-5-6... but there is plenty of non standard mode ( http://en.wikipedia.org/wiki/Non-standard_RAID_levels )... these key enable the non standart intel matrix raid ( http://en.wikipedia.org/wiki/Intel_Matrix_RAID )... the key cannot be modified if you don't have a intel south bridge who end up with a "R" letter ( ICH9R by example ) because the key will not exist...

So, one key is for AHCI, and the second is specific to a Intel raid mode...

My computer have both intel matrix raid and a adaptec raid... have choose to use the adaptec because it have a burst rate of 100mb/s over the intel matrix and more important, it is a hardware raid who don't need CPU power ( intel matrix is a firmware raid who use CPU power )...

Orright, I misunderstood.  I have an AMD based machine, so when yrag told me that I needn't worry about it, that it was for Intel machines, I assumed it was the Intel version of the registry setting I needed to edit..

Oh well, nobody's perfect.

My story:

I bought a new sATA DVD burner around 2 years ago. I installed a new mainboard some time later. Everything was fine except that my DVD drive was not working correctly. It did not read stuff anymore, and almost all reading processes crashed. At some point i figured out, it would work when i disconnected my second, older IDE-harddrive. While testing different things almost to insanity like reinstalling windows, checking drivers yaddayadda, finally i borrowed a very old read-only IDE dvd drive from a friend and kept it for a while. This one worked fine with both sATA and IDE hard disk drives connected, so i concluded this drive is just incompatible with my hardware composition. 

In consequence, this drive laid around for almost a year, just doing nothing but catching dust. One day my sister would tell me, she wanted to have a dvd drive, so i remembered, i still have one lying around that should work, because it did before. So i gave her this one.

Then recently came the day when i had to burn a dvd again. Because the writers had become quite cheap i bought myself a new one finally.

What happened? I had the same error as with the old one....

A random google search accidentally brought me to a site about this AHCI stuff - it was not about solving my problem but it was saying something about this ahci stuff i had never heard before. And it sounded good. So i tried it.

And what happened? Problems gone.

Yeah, great. That would have done the job 2 years ago as well, i suppose...

So HOW THE HECK should a normal guy like me figure out that they did not only change physical but also software stuff like this, when everything seems to work normally withou using it?

It really is satisfying to see, that even a professional software developer has these problems too!

I mean, what are the guys who are constructing this hardware thinking? That everyone who buys it has either a professional education and keeps track of current progresses? Or that our natural clairvoyant abilities make it totally unnecessary to give us a hint in some kind of installation manual?

Comeon, computers are mass products nowadays. Shouldn`t there be a little bit more of user friendliness?

It had been worse in the past, i know that. I still remember the time where you powered the PC and it was giving you very clear instructions what to do now by just saying "C:/" (literal translation: "Just know it, n00b.")

Nonetheless - these things are made for the people using it, not for those who created it. Shouldnt be that hard to figure out what the poeple using it really should already know and what has to be shown to them first.

Brad, thanks for the MFM referance and the stroll down 8 bit memory lane.

For those of you switching to AHCI...disconnecting your USB storage drives while making the switch will allow it to go easier.

Hehe, I'm no expert by any means, but a guy working in an electrical/computer store tried to tell me that if a 7200rpm HDD runs at X speed for data transfers. I'm not going to get any extra speed by connecting SATA 3 or USB3 devices..... because that's as fast as it goes, and you will burn it out if you try to speed up the data move and copy process.

I suggested.... what if the SATA controller protocol was in fact the bottleneck to faster transfer speeds, and that by changing from native IDE in BIOS to AHCI you could in fact improve disk performance... that by connecting a SATA3?USB3 drive you would see more significant gains than their predecessors.  He still insisted that artificially increasing data flow would burn out the drive.  I thought "orright", then, glad I don't come to you for advice."

Well, in fact, the bottleneck can be the drive itself... AHCI don't increase the rpm or directly the data flow... what is greatly reduce is the latency...

"Native Command Queuing (NCQ) is a feature supported by Advanced Host Controller Interface (AHCI). It allows ATA drives to accept more than one command at a time and dynamically reorder the commands for maximum efficiency. NCQ, when used in conjunction with a hard drive that supports NCQ, can increase storage performance on random workloads."

For example, let say that 3 command are sent to the drive... read block a,c,b... if block b is physically between the block a and block c on the drive plate, plate will need to turn two time for read the data... with NCQ ( who work only in AHCI mode ), the electronic of the drive will switch the second and third command and allow to read all the data in a single plate turn...

In fact, it not only reduce latency but it can improve the life of your drive since lower amount of plate turn are needed for read the data...

NCQ is only one of the multiple advantage of AHCI... for example, a other one is the "Hot swap" feature only working with AHCI enable...

"If AHCI is not enabled by the motherboard and chipset, SATA controllers typically operate in "IDE emulation" mode, which does not allow features of devices to be accessed if the ATA/IDE standard does not support them."

As for SATA 3.0... when SATA 1.0 drive was released, the NCQ was very basic and only improve performance in a multitasking environment. NCQ with SATA 3.0 is somehow improved :

"The new specification contains the following changes:
...
    * Isochronous Native Command Queuing (NCQ) streaming command to enable isochronous quality of service data transfers for streaming digital content applications.
    * An NCQ Management feature that helps optimize performance by enabling host processing and management of outstanding NCQ commands.
..."

If you plan to use SSD, best to move to SATA 3.1 who add the following feature :

"Queued Trim Command – allows SATA SSDs to execute Trim without impacting normal operation, improving SSD performance"

In short, SATA drive without AHCI is like having a Formula 1 racing car where the driver is a old guy who never go over the 50km/h.... enabling the AHCI simply replace the old guy by a Formula 1 pilot able to use 100% of the car power... AHCI is not about push a harddrive over his physical limit but about use all the power that the harddrive can give...

As for guy working in computer store, they are usually seller and not computer tech guy... when i have buy my last printer, only a "student job" guy was able to say if the printer will be compatible with my linux OS... important information for me since it was for a 800 euro printer ( color laser all in one )... none of the numerous regular seller from the shop was able to reply my inquiry!!!

That is what I tried to tell this guy... that the IDE emulator was the bottleneck, and that by enabling AHCI, greater potential of the drive can be accessed.  However, he was still insistent that it would eventually burn the drive out.

This guy professed to be some kind of an expert - "I've been around computers my whole life." - and said he had extensive knowledge of both Windows and Mac based machines.  Yeah, right.

My knowledge of computers is not that extensive... like I can build a machine and get it up and running, and I can make various repairs after learning much from the learned folk around here, but can I confidently tweak the BIOS and overclock system settings, no, I can't.  I have some idea because I watched a techie friend overclock my last setup, but I'd still have numerous questions and queries as I went through the process.  Anyway, my point is that this guy [35ish] had been around computers all his life [me, about 7 maybe 8 years], and professed to have extensive knowledge, yet I, a mere novice in comparison, if you compare the time gaining the experience, seemed to have a better understanding than he did.

Sorry to bump an old thread, but I recently had to change to AHCI mode to fix latency issues, but it turns out there is a complication involved to do with a driver called Atapi.sys if you're changing from RAID. Either way I ended up writing on my blog about it, so here are some fairly foolproof instructions about how to sort this issue!

http://blog.earthshine.it/post/15503185497/iastor-or-iastorv-sys-causing-audio-dropouts-pops-and