What determines the DMA mode?

I have a MEGA mini computer running WinXP Pro, 2.8 GHz, 1 GB memory, 2 hard drives (250 GB master & 500 GB slave set on cable select) and a NEC ND-3550A DVD drive (set up as master, not cable select). The DVD drive dropped down to PIO and I had to use the VBA script to reset it to DMA, no other method worked. The VBA script reset it to Ultra DMA, Mode 2 which is probably correct. Everything seems to be working fine now.

Now my question:
I was looking at three new Acer computer at work, all XP Pro, and checked the DMA settings on them.
Oldest (4 months old): The DVD drive(CD burner & DVD reader) was set on Ultra DMA, Mode 4, the HD was set on Ultra DMA, Mode 6
Next (2 months old) The DVD drive (DVD burner & reader) was set on Ultra DMA, Mode 2, the HD was set on Ultra DMA, Mode 5
Newest (1 month old): The DVD drive (DVD burner & reader) was set on Ultra DMA, Mode 4, the HD was set on Ultra DMA, Mode 5
What in the computer determines the different DMA modes? Is it the drive(s), controllers, motherboard or? Can the Mode be changed? What is the benefit of having a higher Mode on a DVD drive, if any?

Both the drive and the motherboard determine the used DMA mode.
Usually motherboards and IDE hard drives support DMA up to Mode 5 (100 MB/s), but certain HDDs and motherboards support Mode 6 (133 MB/s) too. I’m not sure, but i think Mode 6 is not an IDE standard, but rather something that some manufactures introduced.
DMA Mode 6 can be also a Serial ATA device connected in IDE compatibility mode.

The most IDE DVD drives support DMA Mode 2 (33 MB/s), but again the newer drives (like 18x and 20x LiteOn DVDRWs) support Mode 4 (66 MB/s) too.

DMA mode can be changed, but only to modes supported by the system. So you can’t set a DVDRW drive to Mode 4 if the drive or motherboard support only Mode 2, but you can set it to Mode 0, if you want (however i don’t know one would want to do that).
Higher DMA mode means higher transfer speeds between the drive and the IDE bus, thus it is providing more stability. In general, it is recommended to set the devices to the highest supported DMA mode.

The other factor is the IDE cable. A 40wire cable will limit DMA to mode 2 while an 80wire cable raises the limit to mode 6.

Motherboards over the past few years have mode 6 support generally and an increasing number of burners offer mode 4. Some DVD-ROM drives support mode 5 as well eg Asus.

Occasionally a HDD will come with a default setting of mode 5. My Samsung was like this but the manufacturers utilities enable mode switching so mine is now mode 6.

I believe practically all recent IDE controllers will support UDMA6 (133MB/s).

But only Maxtor HDD’s support UDMA6-133MB’s.since maxtor are a bunch of pricks, overclocked the UDMA100 standard & had the hide to patent it. Worse, the patent office upheld it!


I am not sure about Intel. They stuck with UDMA 5.

But only Maxtor HDD’s support UDMA6-133MB’s.
No. Samsung HDDs also support UDMA 6, but it has to be changed using a software tool. Default setting is UDMA 5, just for compatibility with Intel chipsets.


I see high ranked member posting but still not answering the question; What determines the DMA mode?"
I’m not able to answer this in detail because its to complicated (and I don’t know all of it) so I’ll try to put it as simple as possible.

UDMA mode depends primarily on programmed I/O modes clock frequency (this per se determes the speed), ie. the time consumed in ns for a certain operation, interested can learn some basics here.

This programed I/O clock frequency is designed to meet demands of the subsystem aparature that it’s used in. For optical drives almost all producers agree on that the old UDMA-2 mode (speed) is not enough to secure problemfree operation, this has brought us up to UDMA-4.
It’s the same with DMA modes as with other parts of PC, frequencies/speeds have been pumped up.

I’ll not post any comments about HDD’s and UDMA-6 mode, simply because it’s not a approved standard by t13.org.

Thanks everyone for all of the good information, I learned a lot about DMA today.

TimC wrote:
“The other factor is the IDE cable. A 40 wire cable will limit DMA to mode 2 while an 80 wire cable raises the limit to mode 6.”

This is the only thing that I can change, My DVD drive cable is 40 wire, but due to space constraints it is short, sliced and bundled. I have a short 80 wire IDE cable which I might be able to slice and bundle so I could fit it in my computer. I will try this next, although I beleive the motherboard will probably still limit the drive to Mode 2. I will let you know the results of this modification.

I have three other DVD burners, a Lite-On, a Samsung and another NEC ND-3550A, all less than a year old. I use a IDE to USB 2.0 external drive cable to connect them to this computer. How is the DMA controlled thru this USB connection, if at all?

I dont think DMA is relevent if using USB connection.
BTW, here is a little more info on DMA:


I strongly recommend not to touch the cable in this way. I did the same, and a couple of weeks later, my drive wasn’t recognized properly any more.
You should be able to install the cable “as is”, if you want to enjoy your drive. Really.


I’m currently running 3 HDDs on self made single device cables. Self made in that I started with a normal 2 drive cable & cut off the master connection flush at the slave. Certainly reduced clutter in my cases & so far after maybe 6 months they’ve been fine.

These were round cables to start with so I didn’t have to slice them.

The USB to IDE converter will negotiate the UDMA/DMA/PIO mode capability automatically with the drive.

There are some units known to have problems with some drives, but this is often remedied by a firmware update for either the drive, or the USB/IDE converter.

Thank you for your advice, I did what you said and I was able to get the 80 conductor cable in without modifying it. I then installed the Lite-On SHM-165H6S drive (set to Cable Select) instead of the NEC ND-3550A as it is 3/4" shorter (6 5/8" OAL), giving me more room for the cable. This drive also has Lightscribe and will read and write DVD-RAM discs. I restarted the computer and checked my DMA status, this DVD drive is operating at Mode 4. I will try the NEC’s and Samsung in the next few days and see what Mode they end up operating at.
The next step with the Lite-On is to rip a few movies and then record them and see if I can notice any differences, either reading or burning.

The NEC & Samsung are UDMA mode 2 burners. So if you get that all is well.

I tried connecting the other three drives directly and checked the modes. The two NEC ND-3550A’s and the Toshiba/Samsung SH-S162 were Mode 2 as you said.
I then used VSO Inspector http://www.vso-software.fr/products/inspector/inspector.php to surface scan check the same burned movie disc. The Lite-On read at 14.38X max/9.21X avg, the NEC’s were 10.90X max/8.76X avg and the Samsung was a disappointing 7.31X max/4.80X avg. The Mode 4 drive was by far the fastest for this check but it appears that it is more likely that the parameters of the drive itself is more of a factor. The Mode 4 Lite-On was about 5% faster than the Mode 2 NEC’s but the Mode 2 Samsung was about 55% of the speed of the NEC’s.
The Lite-On ripped a 8+ GB movie disc using DVD Decrypter in 16 min 45 sec. I then burned one 3.7 GB movie using DVD Shrink and a Ritex DVD+R 8X disc using the Lite-On and it took 12 min 18 sec but I have nothing to compare either of these two results to yet.


the read speed of a drive is normally not correlated with the DMA mode it is running at. It is more likely the result of mechanical design and firmware.
Just as an example:
Benq DW1650 and Philips DVDR1660 are exactly the same hardware. The Philips reads DVD media slower than the Benq does. Just a matter of firmware here.