HDD: DMA/33 & UDMA/66 speed differences

[1159creampuff]

I have read there is no "real world" difference in noticable speed using a UDMA/66 over a DMA/33 HDD controller. With a 7200rps, 9.0ms HDD and doing heavy audio/visual editing (at least 4 tracks of audio) arn't I better off with the 66? Any technical expounding on the speed differences or personal experiences would be helpful.

[1159creampuff]

So is the internal speed higher for SCSI drives?

[seti]

StorageReview's ata66 vs. ata33 artical (http://www.storagereview.com/articals/9908/990823ata66vsata33a.html)

That artical is a little old, so the difference between the two might be somewhat greater than the 1% show there. However, ide drives have yet to break the 33mb/s line in internal data transfer rate.

The internal data transfer rate, which is the real rate that data can be read from the disk, is often called the sustained transfer rate, while the external rate is called the peak or burst transfer rate. The reason for these terms is that the external rate is usually much higher than the internal rate. So the drive can burst data over the interface at the higher rate when it finds the data requested already in the buffer. But the buffer is quite small compared to the size of the disk (less than 1 MB in most cases), so for a sustained read of any reasonable size, the platters themselves must be accessed, and the overall data transfer rate will drop down to only whatever the drive can handle internally.