Differences in SATA ports' logical ordering on Intel chipsets between IDE and AHCI modes. \ VOGONS

Differences in SATA ports' logical ordering on Intel chipsets between IDE and AHCI modes.

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First post, by LSS10999

Posted on 2025-05-29, 10:03

LSS10999 Offline

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Don't know if this question has been raised before, I noticed that for some reasons, on Intel chipsets the SATA ports are ordered a bit differently in the system when using IDE and AHCI mode.

- With AHCI mode, the SATA ports are ordered correctly. Physical SATA ports 1, 2, 3, 4 correspond to logical disks 1, 2, 3, 4.
- With IDE mode, the SATA ports 2 and 3 are inverted. Physical SATA ports 1, 2, 3, 4 instead correspond to logical disks 1, 3, 2, 4.

So far I've confirmed this on B75 and also X99, though it's possible all chipsets around that period behave the same way. Haven't checked the related sections of the datasheets yet, so I'm not sure if this behavior was already known.

Reply 1 of 3, by Matth79

Posted on 2025-05-29, 13:13

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With SATA not having master/slave, maybe it presents 1234 as in SATA, but in IDE 2 is 1st slave and 4 is second slave, so they present PM, SM, PS, SS - 1324

Reply 2 of 3, by LSS10999

Posted on 2025-05-29, 13:39

LSS10999 Offline

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Matth79 wrote on 2025-05-29, 13:13:

With SATA not having master/slave, maybe it presents 1234 as in SATA, but in IDE 2 is 1st slave and 4 is second slave, so they present PM, SM, PS, SS - 1324

Probably. Some BIOSes do use PM/PS, SM/SS conventions in boot options for SATA ports in IDE mode and it seems to match your explanation. The SATA configuration section in BIOS, however, presents physical ports in correct order regardless of IDE/AHCI.

Been looking at the datasheets but couldn't find anything apparently documenting this ordering difference...

Reply 3 of 3, by fosterwj03

Posted on 2025-05-30, 01:42

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I've seen this behavior on my boards too. I agree that it's a result of how the BIOS emulates the IDE interface. Technically, any of the SATA ports could get assigned as primary master/slave and secondary master/slave. The BIOS is translating the IDE interface calls (IRQ and port address) to the real SATA interface, so the BIOS decides which SATA ports get the call from the IDE driver.

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