DMA vs. PIO

[JudgeGarth]

I've seen references here of setting your burners to DMA as opposed to PIO. What does this mean and why would I ever want to have them set to PIO? These weren't in the glossary on the left.

[dun4cheap]

DMA is direct Memory Accress, pio is much slower software mode. When your drives are in pio mode then busmastering is no longer enabled. Busmastering is a way for the motherboard and eide interface to transfer data without taxing the processor. There is no reason you would want to run in legacy mode (pio).

[guns1inger]

They are data transfer methods. DMA (Direct Memory Addressing) allows data to be transfered from a device - say a HDD - the the memory without having to take it through the CPU first. PIO (Programmed Iput/Output) routes the data to memeory via the CPU.

PIO is undesirable because it slower than DMA, and puts a higher load on the CPU, simply to transfer data.

The default setting for all modern devices is DMA. PIO is a fallback that Windows XP will use if it detects a string of errors reading from a device. If you suddenly find that it takes much longer to read or write when burning a disc, dropping back to PIO is often the cause.

[JudgeGarth]

Thanks, guys!

[redwudz]

Just to add, as this comes up fairly often and may help others, I use this text when someone says they have an unusual slowdown with their optical drives. This is a Windows 'feature' that is supposed to keep the system still running after encountering read errors. Unfortunately, it doesn't reset the mode as automatically as it defaults to it.

To check DMA/PIO mode within Windows:

Control Panel>System>Hardware>Device Manager>IDE ATA/ATAPI controllers.

From there, right click on one of the channels and choose 'Properties>Advanced Settings'. All drives should be DMA mode. The 'Current Transfer Mode' for Hard drives is usually DMA 4-6 and DVD burners DMA 2-4, DVD ROMs usually DMA 2. If you see any in PIO mode, that can slow things down. MS says Windows will default the drive to PIO mode after 6 consecutive read failures.

Changing them back may be easy or complicated. First see if you can change them in that window. If not, I usually right click on the channel the drive is on and uninstall the channel, then let the OS reinstall it by rebooting the computer. This will not damage any files on the computer.

There are other ways to do this, but this usually works the best for me. Sometimes even this doesn't work, then you need to do some Registry editing.

It's surprising how ofter Windows does this sort of reset. Something to check on first if you have a slowdown.

[handyguy]

when looking at your windows desktop, push F1, input DMA in the box, you should get more info.

[ROF]

Is there an advantage to PIO? I know it is slower but I was just wondering if there is something positive related to it.

[jagabo]

Is there an advantage to PIO? I know it is slower but I was just wondering if there is something positive related to it.

No, aside from the obvious like DMA isn't working or a certain device doesn't support it. If you're writing device drivers PIO is easier to program for.

[Dv8ted2]

I've seen references here of setting your burners to DMA as opposed to PIO. What does this mean and why would I ever want to have them set to PIO? These weren't in the glossary on the left.

PIO stands for programmable input-output. It is much much slower.

[kschang]

PIO means your CPU has to move every single byte/word, using up a lot of program cycles. DMA means the peripheral will negotiate the transfer with the mainboard's DMA controller, and do the transfer independent of the CPU, and thus, "much faster".

[oldandinthe way]

The reason it might be desirable to use PIO is that all DMA channels are assigned to other devices. All computers have a limited number of DMA channels, and operating systems do not provide adequate means of sharing DMA channels among many devices.