Windows NT users will have to think twice before enabling the IDE Block Mode feature. Windows NT does not officially support IDE Block Mode and enabling it can corrupt data. Details on this can be found in a Microsoft article about Enhanced IDE operation under Windows NT 4.0.

According to this article, IDE HDD Block Mode (and 32-bit Disk Access) had been observed to cause data corruption in some cases. Microsoft recommends that Windows NT 4.0 users disable IDE HDD Block Mode. Let's take a look at what Microsoft says :-

"Q. Does Windows NT use 32-bit I/O accesses (also known as HDD Block Mode)?

 A. To date, this has been seen to corrupt data in some cases. Therefore, it is not used."

As Windows 2000 is based on Windows NT, it's not known if it's affected as well. It would be quite unlikely though that such an issue would still be affecting Windows 2000. After all, Win9x already supports IDE Block Mode.

Eh... Something Doesn't Make Sense Here...

If you read the above Microsoft Q&A about HDD Block Mode, you would have noted something funny about it. Let's reexamine it. According to it, 32-bit I/O accesses is also known as HDD Block Mode. However, 32-bit I/O accesses, in reality, refers to 32-bit transfers from the IDE controller to the processor. It has nothing to do with HDD Block Mode which refers to multiple sector transfers from the hard disk to the IDE controller.

Further down the Microsoft article is this equally confusing Q&A :-

"Q. Does Windows NT support multiple sector disk transfers for hard drives and removable media devices such as Ez-Drive, ATAPI Jaz, or ATAPI Zip drives?

 A. Windows NT 4.0 supports multi-sector transfers for hard drives, CD-ROM drives, and for removable media."

Now, does Windows NT 4.0 support multiple sector transfers or not?! I don't really know. In one statement, Microsoft says that HDD Block Mode has been seen to corrupt data and is therefore not used (implied : supported). In the other, it says that multiple sector transfers are supported by Windows NT 4.0. So, what does Microsoft actually mean?

It's possible that Microsoft has mixed up 32-bit transfers with multiple sector transfers. It's doubtful that they would mistakenly state that Windows NT 4.0 supports multiple sector transfers if it doesn't in fact support it. That would be a really glaring mistake. So, it's quite probable that Windows NT 4.0 actually supports HDD Block Mode (multiple sector transfers) but they wrongly associated it with 32-bit I/O accesses which they have found to cause data corruption in Windows NT 4.0.

So Do I Enable IDE Block Mode Or Not?

Although it's quite probable that Windows NT 4.0 does not have an issue with IDE Block Mode, Windows NT 4.0 users will still have to think twice before enabling the feature. Data integrity is far more important than performance (especially so for Windows NT users who tend to be running servers, etc...). So, if you are using Windows NT 4.0, disable IDE Block Mode just to be on the safe side.

In addition, it's rare to find both the IDE Block Mode and 32-bit Disk Access BIOS options available together. Usually, only one or the other is found in the BIOS options menu. It's possible that the motherboard manufacturer may have set it so that enabling one enables the other feature as well. In other words, if you enable IDE Block Mode, it's possible that 32-bit Disk Access is enabled as well. In light of this, Windows NT users should really disable IDE Block Mode.

The question now is how much a drop in performance will you incur if you disable IDE Block Mode? That's exactly what we will attempt to find out in this article. If the performance drop is minimal, Windows NT users can disable the feature without fear of a crippling hit in performance. But if the performance hit is really significant, you will have to determine if the performance benefit is worth the potential risk of data loss.

Enough speculation! Let's continue with the tests. :)