DMA - UDMA ?????

[TonyMan]

Having a hard discussion with a friend concerning DMA & UDMA. We both run WIN98 and he says that I should have the DMA box checked for my hard drive in Device Manager. I tried it & upon rebooting it's not checked. When searching around (of course can't find it now!) I swear I read that if the drive is UDMA, then checking DMA could cause a performance setback. When I boot the screen I get showing IDE devices says the drive is UDMA. My position is that I am configured properly for best performance. My friend claims that until I can get DMA checked that something is wrong. Looking for a source of a definitive answer.

Thanks

[Stoormtroopr]

Tony, you are correct. I had assumed the same as your friend, and had a reformat to do because of my lack of computer knowledge. I checked the DMA box in device manager, and could not reboot. One of the fine folks in this forum explained to me about several problems with this DMA box. The way he basically put it was "your BIOS is the definitive judge on DMA/UDMA settings, and windows just attempts to do the same, but poorly"

[AuraEdge]

IS there a link to this? Id like to read up on this. I have an UDMA HD, and Its set as so, but If i check DMA in windows, it immediatly freezes (Prolly an OCing Issue so it doesnt really matter). HOWEVER If i leave UDMA off in BIOS and then turn on DMA in windows, its ok.... In other words, I can have one or the other. At 33-34 Mhz PCI clock tho, I can have both on. Im saying HUH cuz I dont get it. I just wanna link http://www.sysopt.com/forum/smile.gif

[BBA]

Ummm....


Exscuse me..... if you don't use DMA mode in the OS, then you dont get any benefit from UDMA.

If you overclock your PCI bus, then some drives can not handle the increased access rate of DMA and will cause system errors and or slowdowns. Maxtor drives are famous for this. WD and IBM are the least sensitive to overclocking and work fine with DMA set while overclocked.

If you have problems with data corruption when overclocking and using DMA, then you should go into bios, leave UDMA mode on AUTO and set PIO to mode3, then UDMA will still work fine but at 24M/sec as opposed to 33M/sec. Even these rates double for ATA66 drives!

DMA is not evil!


BBA

[hesscomputer]

DMA = DIRECT MEMORY ACCESS
UDMA =ULTRA DIRECT MEMORY ACCESS.
If the drives installed are found to be "real UDMA's" then Win98 will assign the DMA automatically but this has also to have that the Motherboard can read UDMA.
I've installed Windows 98 on I can't remember how many machines and never got any problems with it.
If a drive isn't DMA or UDMA then under certain circumstances there will be problems but this happens only once in history of installing 98 to me.
It does make a difference when running big files (100 Mb up) if DMA is enabled or not.
I fully agree with BBA in this matter but only would not change too much in the bios settings.

[AndreBranco]

how do i know if my motherboard can read udma? i have a wd26400 6.4gb hd but windows didn't check my dma box after reformat and reinstalling windows............ http://www.sysopt.com/forum/frown.gif

[Mitch]

Hi, you can find some interesting info here http://www.pcguide.com/ref/hdd/if/ide/modes_PIO.htm ...Mitch

[AuraEdge]

Oh..hey..yeah guys thanks...I get it now! http://www.sysopt.com/forum/smile.gif

[TonyMan]

OK, I'm mpre confused. I accept that UDMA is faster than DMA, but am I right in saying there is no need to check DMA in Device Manager if the drive is UDMA? I just upgraded my daughters machine to WIN98, her BIOS does not show the drive as UDMA, and I can check the DMA box in Device Manager. This kinda makes me think I'm right in my assumption.

[sunman]

hahah, i have the same doubts as you guys until i visited this website, http://www.benchtest.com/win98.html
BTW, PLEASE back up your registry before enabling DMA in win98 for your HDD becoz once there's some conflict you can't change in safe mode, thus you will have to restore registry settings. some PCI card (eg. my ATM card) has conflict when i enable the DMA support for my IBM HDD and win98 reboots upon loading.
now i have my ATM card remove and i have benchmarked my HDD performance with DMA enabled in WIN98SE. check out the HDD performance~!
http://web.singnet.com.sg/~faxmodem/overclock.htm

[800XL]

DMA box in windows = Direct Memory Access between RAM and the drive controller enable/disable.

UDMA settings in bios = UDMA transfer mode between drive and controller enabled.