A discussion on IDE vs. AHCI

[idata]

There is a lot of information and recommendations online about which storage interfaces and modes

are best suited for SSDs. I'd like to clear up Intel's official recommendation, but first a little

history! Back when PATA or parallel ATA was the standard (and slower) storage interface, BIOS configuration was simpler for end users. The only thing users had to be worried about was about the configuration of multiple devices (each device needed to be slave or master). In 2003, when Parallel ATA was replaced with faster, more efficient and cost effective serial ATA, a new protocol was needed to handle SATA' new capabilities. That's where AHCI comes in.

AHCI is a hardware mechanism that allows software to communicate with SATA drives. To make that transaction smoother, SATA devices were initially designed to handle legacy ATA commands so they could look and act like PATA devices. That is why many motherboards have "legacy" or IDE modes for SATA devices – in that case users are not required to provide additional drivers during OS installation. However, Windows 7 ships with AHCI drivers built in, so soon this mode will no longer be necessary.

But this begs the question: what features does AHCI mode enable? The answer isn't simple, but one of the bigger advantages is NCQ, or native command queuing.

NCQ is a technology that allows hard drives to internally optimize the order of the commands they receive in order to increase their performance. In an SSD everything is different. There is no need to optimize the command queue, but the result of enabling NCQ is the same – there is a performance increase. In brief, NCQ in an Intel SSD enables concurrency in the drive so that up to 32 commands can be executed in parallel.

Other AHCI benefits include: hot plug support, cold device detection, larger LBA addressing and better power management. As you probably know, Intel SSDs have much lower power consumption than HDDs and AHCI can lower their consumption even further with DIPM (we'll leave DIPM for a future discussion!).

Remember that this discussion has thus far avoided the topic of drivers. Luckily, with the release of iRST 9.6, Intel's recommendation has been simplified.

With the newest release of our storage drivers, our SSDs execute OS TRIM commands automatically

(although TRIM is yet another discussion). To get the maximum performance out of your Intel SSD, Intel recommends that users use their SSDs on a platform with a SATA II interface in AHCI mode using Intel Rapid Storage Technology driver version 9.6. Hopefully this clears up some confusion, although if anyone has any questions, I'll do my best to answer!

[idata]

Do Intel SSDs need special driver support?

'No. The standard drivers for any HDD will support Intel SSDs as drop-in components, such as those bundled with Windows*. However, for best performance, a driver that supports SATA Native Command Queuing (NCQ) is recommended, such as the http://www.intel.com/support/chipsets/imsm/ Intel® Matrix Storage Manager (IMSM) driver from Intel.'

http://www.intel.com/support/ssdc/hpssd/sb/CS-029623.htm http://www.intel.com/support/ssdc/hpssd/sb/CS-029623.htm

[mmokk]

Guest wrote:

Thanks SSDelightful,

Is this a Intel implementation? Other SSD vendors specifically discourage users from using AHCI. NCQ is needed only in physical drives where at makes sense to optimize (order) writes according to where the head is. In SSDs there is no head and no latency. Hence NCQ in SSDs is not needed and might disrupt an already optimized traffic flow. See also http://www.ocztechnology.com/res_old/images/Configuring-and-Setting-Up-SSDs.pdf http://www.ocztechnology.com/res_old/images/Configuring-and-Setting-Up-SSDs.pdf.

In short there may be no advantages for NCQ only random halts. Is your discource based on Intel documents or expertise? In that case could you include these in your response?

that guide is outdated. while there is no publication date printed anywhere, if you look at the ssd models that were benchmarked on page 2, they correspond to ocz core series ssd's, which are essentially first generation drives from years ago. things have progressed and improved a bit since then.

plenty of people run their (more modern) ssd's in ahci mode with no problems. with my own personal real world desktop usage patterns, i cannot distinguish any performance differences between ide and ahci modes (though ahci benches higher). ymmv.

[idata]

Only a moron would run an SSD in IDE mode.

[idata]

re: 'only a moron would run a ssd in IDE mode'

Hmmm. I tried to set my P8H67-M LX to ACHI and almost killed my system. To boot back with a BIOS option I had to strip all of my internal SATA II drives, unplug my monitors and attach them to a new internal display channel ... etc. You get the general picture. I think what a certain quoted meant to say was. "In an ideal world, SSD would optimize even the BIOS it was designed to run with." IDE or AHCI, system as well as component stability and security must be a work in progress.

Anyway, up and running now, 03:00 hours PST Friday morning. Take 3 and tech support can sink their teeth in. I guess some of us accept that at this early hour in the first year of SSD's infancy, optimization is a community effort.

[idata]

Mark, what happened exactly? ACHI mode would never "almost killed my system". All it does is pass additional commands to the storage devices.

What OS?