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I know enabling DMA for hard drives can increase overall performance, but should I do the same for optical drives (CD-RW, DVD, CD-ROM)? Will those drives actually benefit from sending data directly to memory, since there transfer rate is already so slow compared to hard drives?
If you don't enable DMA, then the drive operates in PIO mode. Here's an explanation of the advantages of DMA over PIO from StorageReview.com:
So if you don't enable DMA, the drive will run in PIO mode, which uses a lot more CPU power than if you had it in DMA mode.Quote:
<font face="Verdana, Arial" size="2">Programmed I/O is performed by the system CPU; the system processor is responsible for executing the instructions that transfer the data to and from the drive, using special I/O locations. This technique works fine for slow devices like keyboards and modems, but for performance components like hard disks it causes performance issues. Not only does PIO involved a lot of wasteful overhead, the CPU is "distracted" from its ordinary work whenever a hard disk read or write is needed. This means that using PIO is ideally suited for lower-performance applications and single tasking. It also means that the more data the system must transfer, the more the CPU gets bogged down.
Clearly, a better solution is to take the CPU out of the picture entirely, and have the hard disk and system memory communicate directly. Direct memory access or DMA is the generic term used to refer to a transfer protocol where a peripheral device transfers information directly to or from memory, without the system processor being required to perform the transaction. </font>
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Captain Troy D. Pack Rat
`akbar Press
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While the above post succinctly describes the difference between DMA and PIO, there are some additional considerations.
Many CD-R/RW drives flake-out when DMA is enabled. The problem is noted in<a href="http://www.fadden.com/cdrfaq/faq05.html#[5-15-1]">Andy McFadden's CD-Recordable FAQ</a>
My Philips drive works great with DMA enabled, but many that I've seen do not play well with DMA. I hope this helps.
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Blackhawk
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Illegitimis non carborundum.
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[This message has been edited by Blackhawk (edited March 03, 2001).]
I think my drive is one of those. It's a LiteON 12x10x32 BurnProof drive and it works wonderfully, except when DMA is enabled. From what I can tell it just doesn't support it.
What about plain old cd-rom drives? I usually don't enable dma for them either. Another thing u need to take into consideration is the number of dma channels. For instance, LPT1 in ECP/EPP mode uses DMA 1 or 3, one or two hard drives use another DMA channel, sound cards usually grab up another DMA channel. Do I really wanna waste another DMA setting for a cd-rom drive?
I was under the impression that there a limited number of DMA channels, just like IRQ settings. I know two devices can share the same IRQ nowadays with IRQ steering. Is this also the case with dma?
Best way is to check you BIOS POST screen. If it states 'CD-ROM ATA33' then enable DMA and see what happens, if it state 'CD-ROM PIO 4' or 'CD-ROM Mode 4' then leave the DMA off as you are asking for problems that way.
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Darren Wilson
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