It doesn't matter if you are using a bus-mastering driver or not. IDE Block Mode will definitely improve the efficiency of IDE transactions. Although it will not radically improve the throughput of IDE devices as many would have expected, one can still expect a lower overhead for IDE transactions and a slight improvement in throughput. The lower overhead would benefit a user using a non-bus-mastering IDE driver more than it would benefit one using a bus-mastering driver because of the former's reliance on the processor. But I think we would all agree that even a little benefit's better than none. ;)

Throughput-wise, we can only expect a small improvement in the transfer rate of IDE devices. The raw transfer rate should increase in the region of 1-2%. That, unfortunately, would only translate into an overall improvement of system performance of about 0.4% (based on the office applications used in Winstone 99). As mentioned earlier, benefits realized for other software will depend on their reliance on the hard disk. If the software is disk-intensive, it will benefit more but the improvement in performance will never match the increase in raw transfer rate unless the software does nothing more than transfer data.

Now, one needs to remember that increased throughput isn't the main thrust of the feature. So, don't be disappointed at the very small increase in throughput. IDE Block Mode's main advantage lies in the lowering of overhead for IDE transactions. Unfortunately, that benefits systems that still rely on the processor to handle IDE transactions much more than it benefits systems that uses the chipset to do that instead. So, for properly configured systems, benefits realized from IDE Block Mode will be much less apparent than it would be for systems that are not configured properly. This doesn't mean you should stop using the bus-mastering driver though! ;)

If you are using Windows NT 4.0 and have disabled IDE Block Mode to avoid even the slightest chance of data corruption, that's rather good news, I would say. If you have configured your system properly (i.e. by using a bus-mastering driver), you would have more or less avoided the need for IDE Block Mode's main benefit. Thus, you can turn off IDE Block Mode and suffer only a little in the throughput of your hard disks. Generally, the loss in throughput will not be noticeable and any change in performance will only be detectable through benchmarking.

If you are using Win9x, you should enabled IDE Block Mode because there's no risk of data corruption. Improvements will vary from a drop in processor utilization and an increase in throughput (for systems not using bus-mastering drivers) to just a slight increase in throughput (for systems using bus-mastering drivers). Windows 2000 users should be able to use IDE Block Mode without worry of data corruption because there has been no similar warnings about IDE Block Mode for Windows 2000. However, if you are running mission-critical applications and don't mind the loss of some performance, you can disable IDE Block Mode until it is confirmed that Windows 2000 fully supports this feature.