ATA Control Byte and Checksum Values

[Mr Hard Drive]

I recently installed Windows XP Pro on a new (unused) 160GB Western Digital Caviar SE SATA HDD. The motherboard SATA controller was set to IDE in BIOS. At a later date, I managed to install the motherboard supplied AHCI drivers. I then switched the controlled from IDE to AHCI in BIOS. Everything seems to be fine. No issues whatsoever at this time.

I then ran HDS reports on the drive in both modes with the portable version. The results were identical for the exception of the SATA Controller information (as expected), and the ATA Checksum Status (unexpected). In IDE mode the ATA Checksum is VALID, and in AHCI mode it is INVALID. Other than that everything else, and most importantly, the SMART report is identical.

I’m guessing that the INVALID ATA Checksum while in AHCI mode is related to the transition from IDE to AHCI mode, and that the ATA Control Byte and Checksum Value are configured upon drive partitioning and/or OS setup.

A few questions:

- Am I correct in my assumption above?
- Is this to be expected in this particular situation?
- Where are the ATA Control Byte and Checksum Values stored?
- Can it be corrected?
- Do I even have to be concerned about it?

Thanks in advance for any assistance provided.

[hdsentinel]

> I’m guessing that the INVALID ATA Checksum while in AHCI mode is related to the transition
> from IDE to AHCI mode, and that the ATA Control Byte and Checksum Value
> are configured upon drive partitioning and/or OS setup.

No, these values do not depend on the AHCI-IDE transition itself (the CHANGE of the mode) and completely independent from the drive partitioning/formatting, independent from the contents of any data sector.


If you check the Help:

https://www.hdsentinel.com/help/en/13_info.html

it has a note about these fields:

Note: Hard Disk Sentinel checks if the ATA information table is completed and the checksum of the table is correct. The latter ensures that the information detected and displayed are correct. If this is not true, it is possible that some values may not be correctly reported by the hard disk (for example the performance value, the UDMA transfer mode and serial ATA properties). There is a warning displayed in these cases.
Invalid ATA Control Byte or ATA Checksum Value does not affect the detection and display of health and temperature values.

Generally these values depend on the driver installed and used for the disk controller (motherboard chipset) which manages the hard disk drive.

Yes, the IDE-mode driver and the AHCI-mode driver may work slightly differently: they may affect how the identification information could be read from the disk drive when the IDENTIFY DEVICE command used.


> Is this to be expected in this particular situation?

It is not expected, but according the experiences, this is completely normal. No need to worry about it, as it does not affect how the health and the complete S.M.A.R.T. data could be detected.


> Where are the ATA Control Byte and Checksum Values stored?

These are the last two bytes of the IDENTIFY DEVICE command response.
You may check in this file:
http://www.t13.org/documents/UploadedDo ... _ACS-2.pdf
see page 141 "Integrity word" which contains the checksum and the validity indicator (= control byte)

This is an older standard, but should show the details if you're interested (newer standards may be not publicly available).


> Can it be corrected?

It does not mean something is bad, so there is no need to "correct" or fix it in any ways.
If you change/update the disk controller driver, then things way work differently, so it is possible that the values will be different after a driver change/update.


> Do I even have to be concerned about it?

No, you do not need to worry about them.

[Mr Hard Drive]

Thank you kindly for your quick response.

I work with several legacy machines. HDS Pro works very well, and serves my needs satisfactorily.