I just put a new power supply (ANTEC 430 Truepower) in one of my computers to, hopefully, solve a OS stability problem - too many Blue Screens of Death with WinXP no less. While I was at it, I threw another DVD writer in the box (Pioneer DVR 108) so now I have 4 optical burners on the 2 ATAPI/IDE channels - a DVD-ROM, a CD writer, and 2 DVD writers. There's a SATA RAID 0 setup for the hard drives on another controller. Anyway, I ended up with one DVD writer (a BTC 8X OEM) as master, and the DVD-ROM (Pioneer slot type) as slave, both on the IDE primary channel. The CD writer (a Lite-on 52X) is master and the new DVD writer (Pioneer 16X & DL) as slave on the IDE secondary channel. I deleted and reinstalled the secondary IDE channel so all the devices end up using DMA mode. All the devices seem to work fine. I don't understand, however, why the devices on the primary IDE channel use DMA-4, while both devices on the seconary IDE channel are assigned DMA-2. Is there any differences between DMA-4 and DMA-2 I should be concerned about these different DMA modes with my setup? Sorry for the rambling question...
Since nobody responded to my question - I "googled" the question and the answer is... As far as DVD writers go, it makes no difference if you use DMA mode 2 or mode 4. The limiting factor is the DVD writer's data transfer rate, not the ATAPI/IDE channel DMA mode 2 or 4 transfer rate. So what are the transfer rates? A DVD writer transfers (i.e. writes) at 3.2 MBs/sec at 2.4X, 5.4 MBs/sec at 4x, 10.8 MBs/sec at 8X and 21.6 MBs/sec at 16X. DMA-2 has a transfer rate (i.e. reads from hard drive) of 33.3 MBs/sec and DMA-4 weighs in at 66.7 MBs/sec. So, even if your DVD writer is burning at 16X, the ATAPI/IDE controller set to DMA-2 mode still supplies the data plenty fast enough (i.e. 33.3 is greater than 21.6). This explains why I see no differences burning DVDs where one writer uses DMA-2 and the other DMA-4. I forgot to mention why the computer assigns DMA-2 to the one writer on the secondary ATAPI/IDE channel. It's the ribbon connector cable - unless you use the 80 pin ribbon cable (the one with blue, grey, and black connectors), WINXP limits you to DMA-2. You need that 80 pin cable to allow DMA-4. My cable is the 40 pin type (all black connectors), so I'm limited to DMA-2. I think I've beat this subject to death...
The only issue when worrying about DMA modes is when there is some sort of multiple transfer... IE primary master is HD and primary slave is DVD burner. Then the line gets clogged because the data has to transfer down from the HD and back up to the burner, through the ribbon twice. Had some problems with a CD burner having this problem a couple years back. Also, I believe that when there are two devices on one cable, the DMA mode defaults to the highest supported by both devices. so if one supports 4 and the other only 2, it will be forced into DMA mode 2.
