temp file drive

Here's what the Help says about choosing drives for temp files:

"Primary Temp Specifies the main folder for temporary files. Ideally, it should be on your fastest hard drive.

Secondary Temp Specifies the secondary folder for temporary files. For best results, specify a different physical hard drive than the primary temp folder."

Okay, I've chosen an external hard drive for my primary temp drive, simply because it has bags of space compared to the other two drives.  I'm no computer wrangler, but I doubt it's my fastest drive.  However, yesterday evening, I recorded a number of things and there were no problems.  So, I'm wondering what's involved in choice of drive for temp files and how important the speed issue is.  Is the speed important because of stuff being written TO the temp file or because of stuff being read FROM the temp file.  Or both?

It's exactly as you'd presume -- writing to the temp file when making new recordings being the most significant.

Well now, lest I lead you astray: in AA2 & 3 there is no background mixing, so reading from temp files is less prone to be necessary any more.  In fact, with direct-to-file recordings made in AA2/3's multitrack view, there aren't any temp files to be written to.

Hmmm...  one thing hasn't changed: when recording many tracks at once, multiple physical locations help.  So if direct-to-file, then split them across 2+ locations.  If using a temp file mode, then have two temp locations on separate drives.

Methinks the temp drives Help isn't up-to-date, now that I've muddied the waters with all of this.

You know, I think you haven't muddied the waters.  No Muddy Waters.  I think you've clarified it for me, in fact.  When recording, there aren't any temp files, cuz the whole thing's done direct-to-file. 

So what are the temp files for?  For EV undos?  Does Au use temp files for realtime effects in MV?

So what are the temp files for?  For EV undos? 

Yes. But nobody's got the direct recording story quite right yet... direct-to-file recording only happens in MV. In EV, recording is still to a temp file - which is why you can start recording directly from the record button.