Simple Advice on HDD & IDE controller issue requested

Hi,

I've just had a compromised primary IDE controller problem in Win98SE, MS-DOS compatability mode and no drives reported in Device Manager and all that, in an older P2 440LX based system. We have managed to solve this eventually thanks to some great support in the Win98 forum. I have 2 HDDs on the primary and a CD-ROM on the secondary. The HDDs are both venerable units, 8.4Gb & 3.2Gb and both ATA33, reported by BIOS as UDMA4 and UDMA2. Master/slave relationships are correctly set.

In the end the solution came down to exploring in safe mode and finding that in Device Manager both HDDs are reported as type 46, and that the boot drive C:, although being identified in the BIOS correctly, was being reported twice by Windows Device Manager. Both versions were reported as C: but one was type 46 and one was type 47. I deleted the type 47 as this seemed the odd man out (scientific or what?), deleted the IDE master controller, (Intel 82371AB/EB from their 440LX chipset), and rapidly restarted before lockup. Hey presto, win98 finds the controller, reinstalls and Device Manager now reports the primary is ok and I have 2 HDDs reported both type 47!

So ok I'm up and running again, but this has happened to me before and it could not be resolved then. It took an unrelated reformat/reinstall to eventually sort it out. Any problem which reoccurs and I don't know why leaves me worried and looking for the answer. So here are my queries and I wonder if anyone can offer advice:

1) What is the difference between type 46 and type 47 HDDs?

2) Should I leave DMA unchecked or checked in the HDD's Settings dialog in Device Manager and why? Although I would have thought that I should check this box to enable DMA transfers I have a feeling that checking it may have kicked off the whole sorry saga.

3) I understand that ATA33/66/100/133 is an increasing speed standard but how does the DMA/UDMA side of this relate to the ATA?

Any offering gratefully received.