This is inspired by this post..

My experience could be wrong or my interpretations wrong..  But this is
usenet, it's open for people to correct it, ignore it,  or say it's
rubbish

I can't remember the details of my old experience, I did jot it down so
will check.. Actually, I think I remember..

I'll discuss 2 boards I saw..

Board 1-

I had a MBRD with 2 SATA connectors and 2 IDE connectors.

you can install 2 SATA AND 2 IDE or one SATA and one IDE.

Think of it like  SATA(allows 2 'cos 2 connectors).    IDE1(allows 2) ,
 IDE2(allows 2).
If you want to use SATA with IDE, you lose one of your IDE connectors.

When doing SATA & IDE, it treated the 2 SATA connectors as an IDE
master connector and an IDE slave connector. Of the same IDE channel..
And it only allowed 2 IDE connectors. So if you installed one SATA
drive, then it disabled one IDE connector. So it's like you had 2 IDE
channels.

I think it also had an option along the lines of choosing which is
channel 1 and which is channel 2.  Like, whichis the primary and which
is the secondary. This is relevant 'cos usually people boot off
primary. Also, it's relevant to Norton Ghost 'cos that looks at drives
and labels them 1,2,3,4 in the order they are listed in the BIOS.  I
say 1,2,3,4 if you have optical drives installed.

So, even in that set up.  You could probably put 4 drives in.   2 SATA
and 2 IDE.  'cos when you use SATA with IDE, it disables one channel.
So you could put 2 drives on each IDE channel.. one on the so-called
IDE channel (really 2 SATA connectors).  The other 2 drives on one of
the actual IDE channels.  And the other IDE channel is disabled

Board 2

This SATA board I saw, had 2 SATA connectors and 1 IDE connector..

So, you could  use them both.. think of board 1, but this time the
board won't let you mistakenly try to use  SATA+IDE1+IDE2  'cos there
is no IDE2.