Hardware Reference
In-Depth Information
compatibility mode, but you might be missing out on the performance offered by the ad-
vanced capabilities your hard drives support.
Althoughthefirsttwooptionscanworkinmostsituations,Ithinkthebestoverallsolution
is to simply create a custom Windows XP installation disc that already has the SATA
AHCI (and even RAID) drivers preinstalled. This can be accomplished via a somewhat
tedious manual integration process for each set of drivers, but to make things really easy
youcanusethemenu-drivenBTSDriverPacksfrom www.driverpacks.net tointegratevir-
tuallyallthepopularmassstoragedriversdirectlyintoyourWindowsXPinstalldisc.The
DriverPacks allow you to easily add all kinds of drivers to your Windows XP installation
discs. For example, in addition to the mass storage drivers, I like to integrate the various
processor, chipset, and network (both wired and wireless) drivers because all of these still
fitonaCD.Ifyouarewilling tomovetoaDVDinstead ofaCD,youcanfitalltheavail-
able DriverPacks on a single DVD.
SATA Transfer Modes
SATAtransfersdatainacompletelydifferentmannerfromPATA.Asindicatedpreviously,
the transfer rates are 1.5Gbps (150MBps), 3.0GBps (300MBps), and 6.0GBps
(600MBps),withmostdrivestodaysupportingeitherthe1.5GBpsand3.0GBpsrate.Note
thatspeedsarebackwardcompatible—forexample,alldrivessupportingthe3.0GBpsrate
also work at 1.5GBps. Note that because SATA is designed to be backward compatible
with PATA, some confusion can result because the BIOS and drives can report speeds and
modes that emulate PATA settings for backward compatibility.
For example, many motherboards detect and report a SATA drive as supporting Ultra
DMAMode5(ATA/100),whichisaPATAmodeoperatingat100MBps.Thisisobviously
incorrect because even the slowest SATA mode (1.5GBps) is 150MBps, and Ultra DMA
modes simply do not apply to SATA drives.
PATA and SATA are completely different electrical and physical specifications, but SATA
does emulate PATA in a way that makes it completely software transparent. In fact, the
PATA emulation in SATA specifically conforms to the ATA-5 specification.
This is especially apparent in the IDENTIFY DEVICE command that the autodetect routines
use in the BIOS to read the drive parameters. The SATA specification indicates that many
of the items returned by IDENTIFY DEVICE are to be “set as indicated in ATA/ATAPI-5,”
including available UDMA modes and settings.
The SATA 1 specification also says, “Emulation of parallel ATA device behavior, as per-
ceived by the host BIOS or software driver, is a cooperative effort between the device
and the SATA host adapter hardware. The behavior of Command and Control Block re-
gisters, PIO and DMA data transfers, resets, and interrupts are emulated. The host adapter
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