The Sawtooth can see 128 gigs of a formatted drive, a larger drive will always appear as 128 gigs. You can pop in an IDE PCI card and get large drive support, but you have to have your System drive on the motherboard bus. There is no restriction about 32 gig drives.
The QuickSilver Macs are more complicated. They straddled Apple's logic board change, the first versions could not see large drives, the later ones could. Your 733 MHz was one of that went both ways. If I remember right, I think the "education" model had large drive support. Your model probably does not.
I have never seen anything about that the system has to be on the motherboard bus. Most if not all cards support booting. If I would get a card I would get a SATA card not a IDE133 as SATA drive will fit in your next computer a PATA will not
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The QuickSilver Macs are more complicated. They straddled Apple's logic board change, the first versions could not see large drives, the later ones could. Your 733 MHz was one of that went both ways. If I remember right, I think the "education" model had large drive support. Your model probably does not.