Samsung 840 White Paper page 8

Maximize SATA Capabilities with AHCI
AHCI, Advanced Host Controller Interface, is an open interface championed by Intel to allow the use of advanced SATA
features (e.g. NCQ, hot plugging, power management). Basically, it defines a standard method for storage devices from
various vendors to communicate with the host system, allowing software engineers to take advantage of specialized
functionality. In order to enjoy the full performance of your Samsung 840 or 840 PRO Series SSD, AHCI mode must be
enabled on your system through the BIOS.
If AHCI is not properly configured on your system, the Random Read/Write performance of your SSD will be limited to a
Queue Depth of 1 (QD1), severely limiting the performance improvements you will notice over a conventional Hard Disk
Drive (HDD) while multi-tasking (by 80-90%). Since the latest versions of Windows, including Windows Vista and Windows
7, include standard AHCI drivers, there is no need to install AHCI drivers manually. Some older systems, however, may
not support AHCI even if they are equipped with a SATA 3 (6Gb/s) interface. Samsung's Magician software can help you
determine whether or not AHCI is supported and/or enabled on your PC.
How do I enable AHCI?
Most modern PC systems support AHCI mode and enable it by default. If it is not enabled on your system for some
reason, however, you can manually enable it via your computer's BIOS. The procedure will vary slightly depending on the
BIOS version on each system, but the general steps are the same: Restart the computer and press the appropriate key to
enter the BIOS (this is usually DELETE, F2, or F10); Find the section for "Integrated Peripherals" or "Storage configuration;"
Change "Configure SATA as" or "PCH SATA Control Mode" to "AHCI." Consult your PC's user manual for instructions for
your specific machine.
Ideally, AHCI mode should be enabled via the BIOS BEFORE installing the Operating System (OS). On newer systems,
this is generally the case. If it is not, and AHCI is enabled via the BIOS for a Windows Installation that was not originally
configured for AHCI, it is not uncommon for stability problems to arise. Windows XP does not include native AHCI drivers,
making it more complicated to enable AHCI mode because it is the user's responsibility to locate and install the correct
AHCI drivers for the OS. In general, PC chipset vendors (e.g. Intel, AMD, nVIDIA) maintain their own AHCI drivers for
Windows XP users. It is best to consult the website of your motherboard vendor or PC manufacturer to be sure.
What specific advantages does AHCI provide to Samsung SSDs?
Significantly Lower Power Consumption
AHCI mode is required for Samsung's SSDs to demonstrate their superior power consumption. This is because, without
AHCI, the SSD cannot communicate with the host system to take advantage of advanced power management features
like Host-Initiated Power Management (HIPM) and Device-Initiated Power Management (DIPM). Maintaining the physical
SATA interface (called the PHY) consumes a considerable amount of power, and HIPM and DIPM allow for the PHY to be
put into a reduced power mode. After some predetermined period of inactivity, either the host or the device can signal
the PHY to enter its reduced power state. Samsung's 840 and 840 Pro Series SSDs make aggressive use of DIPM to put