9 Replies Latest reply on Jun 24, 2011 5:35 AM by DuckieHo

    A discussion on IDE vs. AHCI


      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!