The Explorer: The Nearly Secret DMA Can Speed Up Your Drives

CDs, DVDs, and CDRs, Too!
Curiously, although most newer CDs (and CD-Rs and DVDs) support DMA operation, there's not a lot of information on its use -- except for the usual dire warnings. And the warnings are amplified with CD-R: If you take things at face value, you might assume that, with DMA enabled, you'll never burn another CD again.

But I've been using DMA on all my hard drives and CD-type devices -- including CDRs and DVDs -- for some time now. With most hard drives, I've benchmarked the before and after speeds, and found an immediate 5 to 15 percent speed increase with DMA enabled. And some things (loading large apps, for example) feel much, much more than just 5 to 15 percent faster. I've had no trouble whatsoever using DMA.

Because DMA is a way to bypass the CPU, you might suspect that DMA's benefit is greatest on slower systems. And while there's some truth to that -- the more CPU-bound your system is, the more speed-increase you may see from DMA -- even the fastest system can benefit. On my newest system, for example, a 1.2GHz Athlon box with 256MB of RAM and an Ultra-ATA hard drive, manually enabling DMA speeded my hard drive read operations by almost 10MB/sec, and speeded writes by 13MB/sec.

But due to the vagaries of OS, hardware, and driver support, not every system sees DMA speed improvements all the time: The only way to be sure is to do your own before and after tests, using something like the free drive-throughput tests at WinTune to benchmark your before and after results. (You also can use other reputable hard-drive tests, such as those in Norton Utilities, or on the free PC Pitstop site.)

Want more info? We originally covered DMA access in this space more than a year ago. That article will tell you about the five different "modes" of drivewoperation, master/slave issues (when you have more than one device on an IDE cable) and lots more.

Ready To Try?
If you want to try DMA mode, visit the vendor site for your system and/or hard drive brand and search for information and advice on whether or not to use the DMA option. Or try this: Your system's BIOS information may show whether or not your have a DMA-capable drive.

If the answer is clearly yes or no, then stick with what the manufacturer says. But if the answer is unclear, and if you have a good backup, you might want to give it a try. Microsoft says that under Windows, if your drive doesn't support DMA transfers, nothing bad will happen, and the drive will simply revert to non-DMA mode. But I never, ever counsel you to trust your data to what's "supposed" to happen: Always make a backup of your essential files first, just in case.

Chances are, you probably can enable DMA on some or all of the drives and CDs that currently do not have it enabled, and pick up a nontrivial amount of speed that you've paid for -- but haven't been getting!

Give DMA a try, and then join in the discussion area to tell us what your results were!

To discuss this column with other readers, please visit Fred Langa's forum on the Listening Post.

To find out more about Fred Langa, please visit his page on the Listening Post.