Hello spirit,
Because they are both the same brand of drive and same speed (i'm assuming), I would go with:-
20GB OS Primary IDE Master
80GB Data Primary IDE Slave
CDrom Secondary IDE Primary/Slave whatever.
The reason is, IDE cannot do simultaneous read/write regardless of spreading drives across IDE controllers (it doesn't work like SCSI) E.G.-
Read from IDE1, Write to IDE2 - does not occur simultaneously, rather it will read first from hardrive on ide1 and then write to harddrive on ide2 then go back to ide1, read a bit more then write to ide2 etc, etc.
The addition of an extra ide controller is pretty much only to facilitate connection of extra devices to get around the 2 devices on one ide.
The people building your computer should know this.
PS, someone please correct me if i'm wrong.
