Multiword vs. Ultra DMA mode - what's the difference?

[wpenhall]

The VIA IDE Tool shows my Lite-On LTR-40125S (40x12x48) CD-RW running in "Multiword DMA mode 2." It appears that I have the option to change it to Ultra DMA mode 0, 1, or 2. It is in the master position of my primary IDE channel with no slave.

What is the difference between multiword and Ultra DMA? What considerations should go into selecting the mode? Should I change this setting?

BTW, I have the Epox 8K5A3+ mobo if that makes any difference.

Thanks!

 

[dszd0g]

If I recall correctly, one of the features that was added in UDMA 2 was the ability to transfer more than one word of data at a time (multiword mode).

Now there is "regular DMA" and "Ultra DMA" Mode 2, where regular is single transition clocking and ultra is double transition clocking. However, both are multiword so that doesn't tell much.

 

[Pariah]

All DMA transfers are multiword transfers. The last single word DMA transfer maxed at about 8MB/s. Ultra DMA is simply a progression of multiword DMA transfers and begins 16.6MB/s (UDMA Mode 0) which is the same speed as the highest non-Ultra DMA (Multiword DMA mode 2) transfer speed. UDMA mode 1 is 25MB/s (not commonly used) and mode 2 is 33MB/s. If you're not having any problems with your drive, just leave the settings alone.

 

[dszd0g]

O.K., multiword DMA is often used to describe when it is running single transition instead of double transition:

PIO Modes: 0 [3.3MB/s], 1 [5.2MB/s], 2 [8.3MB/s], 3 [11.1MB/s], 4 [16.7MB/s]
Multiword DMA Modes: 0 [4.2MB/s], 1 [13.3MB/s], 2 [16.7MB/s]
Ultra DMA Modes: 0 [16.7MB/s], 1 [25.0MB/s], 2 [33.3MB/s], 3 [44.4MB/s], 4 [66.7MB/s], 5 [100.0MB/s]

Sometimes devices will fall back to single transition if they cannot work in double transition mode. One needs an 80-wire (still 40-pin) cable to operate in double-transition mode. I am not sure whether that drive supports double transition mode or not.

 

[Pariah]

"One needs an 80-wire (still 40-pin) cable to operate in double-transition mode. I am not sure whether that drive supports double transition mode or not."

You only need the 80 wire cable when running UDMA mode 3 or higher since that was the first transfer mode to increase the clock rate above the speeds of multiword DMA mode 2. If the drive supports any mode of UDMA it will support double transition clocking.

 

[wpenhall]

Thank you for all the input, but I'm still not sure if this is something I should try to change. I do have an 80 pin cable connecting my CD drive to the ISE controller, but my drive apparently still defaulted to multiword DMA mode 2. My WD 120 GB SE defaulted to UDMA mode 5.

So how can I find out if the Lite-On supports UDMA? And should I really care? Would I really notice a speed increase with either reading or burning?

I'm not having any problems with the drive so I'm tempted to leave well enough alone.

 

[dszd0g]

Multiword DMA Mode 2:

16.7MB/s * (1024KB/1MB) * (1X*s/150KB) = 114X

UDMA Mode 2:

33.3MB/s * (1024KB/1MB) * (1X*s/150KB) = 227X

I don't think we'll be seeing a 114X CD-ROM anytime soon. I wouldn't worry about it.

I don't think it would even make a noticeable difference with a buffered read.

 

[Pink0]

My LG burner also is stuck in Multi word DMA mode 2 and according to reviews does not support UDMA 33. This is fine. It benches just great and performs like a champ anyway. I don't think it's anything you need to worry about.

 

[wpenhall]

Originally posted by: dszd0g
Multiword DMA Mode 2:

16.7MB/s * (1024KB/1MB) * (1X*s/150KB) = 114X

UDMA Mode 2:

33.3MB/s * (1024KB/1MB) * (1X*s/150KB) = 227X

I don't think we'll be seeing a 114X CD-ROM anytime soon. I wouldn't worry about it.

I don't think it would even make a noticeable difference with a buffered read.

Ahhhh - now I see. Thank you for the explanation (a little math really can go a long way...).