SATA Master/Slave with IDE Emulation

Core 2 Duo E6300 @ 2.2ghz
Asus P5G41-M LE
Vista Ultimate 64 Bit

SATA Port 1: WD 500 GB Caviar Blue SATA(Boot drive)
SATA Port 2: Hitachi 2 TB SATA
SATA Port 3: Asus DRW-24B1ST SATA DVD-RW
SATA Port 4: Empty

Primary IDE Master: WD 250 GB PATA
Primary IDE Slave: WD 160 GB PATA

ICH7 southbridge which means no AHCI or RAID.


I just bought a Hitachi 2TB drive today and I noticed when looking at the boot order in BIOS that there are Designations before the drive models in the list.

For example: PM was listed in front of the WD 250 GB hard drive, PS in front of the WD 250 GB hard drive, 3M for WD 500 GB SATA(Boot drive), 3S for Hitachi 2 TB SATA, and 4M for the DVD Drive.

So I figure the M and S means Master and Slave.

I look into Device manager and I see 3 IDE channels. I look at them and I see two of the channels with two devices each. The 3rd channel shows one device.
Both the channels with two devices says Channel 0, The channel with the DVD drive says Channel 1.

I have no idea what all that means but I'm just putting it out there.

So it appears that I'm in IDE Emulation and have no choice.(correct me if I'm wrong)

Will I have the same limitations with my two SATA drives(SATA Port 1 and 2 running as Master and Slave) as if I were running two hard drives on the same ribbon as master and slave and not being able to write to both drives at the same time because windows sees the drives as Master and Slave? or will I be able to write to both SATA drives simultaneously?

If I'm confusing anyone just ask, thanks :)
6 answers Last reply
More about sata master slave emulation
  1. Don't worry. The "problem" is that the mobo maker has used old terminology on new technology, and it is confusing!

    Your mobo has one IDE port, and it has two devices connected to it, correctly identified as a Master and a Slave. No problems there.

    Your mobo has four SATA 3.0 Gb/s ports labelled 1 though 4. They truly are SATA ports, BUT the mobo maker and its BIOS supplier chose to use internal names for them as if they were more IDE ports numbered 3 and 4. (They skipped #2, because most systems allow for 2 true IDE ports, even though your mobo does not have the second one.) And then they "grouped" them for label purposes, calling SATA1 the Master of the 3rd IDE port, and SATA2 its Slave, etc. But the truth is, these are NOT IDE ports - they are SATA 3.0 Gb/s ports and do perform that way.

    Now to the matter of IDE Emulation. This is a feature commonly available in BIOS's to provide a work-around for users of Win XP and previous versions. They have no native way to handle AHCI devices like SATA drives, so they require the installation of a device driver for those. An alternative is this BIOS trick - the BIOS can be set to make a true SATA device downgrade itself slightly to behave exactly like an IDE device that Win XP DOES understand and use, no special drivers needed. But you are using Vista, which DOES have built-in drivers for AHCI devices, so you don't need that. The way you make that choice (usually made before installing your OS on a HDD) is in the SATA port configuration. See your mobo manual, page 2-8, Section 2.3.4. Your mobo allows you to configure each SATA port independently. The choices are: [S-ATA], [S-ATA + P-ATA], or [P-ATA]. IF you were using XP, you might have to chose the [P-ATA] mode for IDE Emulation. But since you are in VISTA, your OS could handle treating the HDD's in [S-ATA] mode to get all their functionality. HOWEVER be careful about this. If you look in your BIOS Setup screens and find that these ports are already set to [P-ATA], do not change them. Vista could have trouble figuring out how to deal with SATA devices that it was using a PATA devices. There are ways you can find on the 'net to change from IDE Emulation mode to AHCI (or SATA) mode by editing a few items in the Windows Registry. But if you're not into that stuff, leave your SATA port settings as they are.

    Now, suppose they are set to [P-ATA] so that you are using IDE Emulation mode - what is the harm? Not much. Your SATA drives will still function faster than most IDE drives. You won't have the use of Hot Swap support or NCQ, and maybe a couple more obscure AHCI features, but those may not be important at all for what you are doing with this computer. If you think they may be, and if you think you need to switch to true AHCI mode (that is really what a SATA drive is - an AHCI device), check into the details of making the switch.

    You should not have the device contention issue you are worried about. IDE ports do have that, as you say, because two devices share one port and data cable and controller. But SATA controllers are built to handle four devices at once, and all four are on their own individual ports - no sharing.
  2. Thanks for the detailed answer, Paperdoc.

    So I assume Windows won't say hey they're on the same channel and stop the two sata drives from working simultaneously?

    Also I was pretty unsure what the [S-ATA], [S-ATA + P-ATA], or [P-ATA] options were for. I googled it before I installed my o/s and it said something about native support. as in XP or above. And since I was using Vista I just chose [S-ATA + P-ATA]

    What does that mode do?

    I just figured if I selected Enhanced I would have been in SATA mode but all that stuff in BIOS confused me.
  3. Umm a slight correction.

    SATA is exactly that, the ATA packet technology over a serial connection. It's more akin to SCSI then IDE.

    Second is that running in "IDE Mode" WILL result in performance degradation. The bandwidth may be 3.0Gbps, but a single HDD will never saturate a ATA133 interface anyway. The degradation comes from the fact the OS must talk to the disks as though they are IDE devices and not SATA, meaning none of the advanced SATA commands are available. There was a reason we shifted from IDE to SATA and the slimmer cable is actually the lessor of the reasons. In IDE the master / slave relationship is still enforced at the OS level, even though there is no technical requirement for it at the BIOS level. Whichever device is designated the Master must still yield the "bus" over to the slave for communication, even though the "bus" is a completely different connector. This is a natural result of the legacy IDE emulation.

    Windows XP is under no restriction for SATA devices. People are just being lazy.

    Vanilla XP lacks a SATA miniport driver, and SATA controllers look identical to SCSI controllers from the OS point of view. Therefor you must treat the same as a SCSI controller during installation, meaning you have to read the manual. Inside the manufacturers driver CD will be a piece of software that you run. It will create a floppy disk that contains the storage controller mini-port drivers required for NT to talk to the disk. During installation hit F6 insert disk and select the appropriate controller option, it will load the mini-port drivers and *POOF* native AHCI / SATA disks inside Windows XP.

    "Legacy IDE" mode isn't for XP, it's for DOS and other OS's that don't support install time loading of storage mini-port drivers. There is absolutely zero need for modern systems to have it enabled. XP should be set to AHCI with the storage mini-port drivers loaded.
  4. so who's right here in regards to whether windows will prevent both sata drives running as master and slave to work simultaneously?
  5. kxracer said:
    so who's right here in regards to whether windows will prevent both sata drives running as master and slave to work simultaneously?


    Windows don't prevent anything, the BIOS and drives themselves will do that. That is just how IDE works, the slave device must wait for the master to authorize it to talk on the channel. Originally this was done because both drives shared the same bus and there needed to be some form of control. And even though the SATA disk are each connect to their own bus physically, they still talk on the same logical bus. It's the down side to emulation.

    Suggestion is that unless your running DOS, never EVER run a SATA drive in legacy mode.
  6. Well for now I just connected the 2TB Hitachi drive to SATA port 4. If any of you have expert information supporting your opinions feel free to post the link here, thanks :)
Ask a new question

Read More

SATA Western Digital Storage