On 2004.04.03 19:27, adam@thebowery.co.uk wrote:

The (very) unscientific results of this showed that whichever way I tried this the job took the same amount of real time in seconds to complete (around 2m19s) (this I presume is that even without using dma the dvdburner can shunt more than enough data over the IDE bus), the difference was that when I wasn't using dma the amount of cpu usage as system (according to top) was pegged at around 60-70% of cpu with the idle time at about 40-30% and a load average of around 0.89 and when using dma the system time dropped to under 5% with an idle time of about 95% and a load average of 0.60ish. This is on an athlon 1700+ machine and a via kt400 motherboard chipset with everything connected up nicely with the best type of cables etc. etc.

OK, so that's a data transfer rate of 3.27 MB/s and yes, at that speed PIO can keep up at the expense of more CPU time used. As the device gets faster the same is not true. Doing a similar test for a hard disk I remember getting rates of approx. 5 MB/s for PIO and approx. 25 MB/s for DMA. For a DVD burner running at 11 MB/s the difference would be important.

Steve.