Ohne DMA muss die CPU die Speicehrblöcke zwischen den Geräten hin- und herschaufeln. Mit DMA können das machen Geräte direkt tun. Besonders bei Laufwerken und Grafikkarten wirkt sich das erheblich in der Geschwindigkeit aus.
For „ruckelfreie“ DVD: hdparm /dev/hdc (when DVD is hdc) 32-bit access and DMA should be on (1)
else try to turn it on:
hdparm -c 1 /dev/hdc (32bit) hdparm -d 1 /dev/hdc (dma)
see configuration of dma etc. /eg. harddisc): cat /proc/ide/hda/settings
By the way, if you want to review the boot messages, run „dmesg“ just after booting up.
It's probably that the kernel is disabling DMA transfers, because they often don't work right on many IDE controllers. You can try reenabling it by installing „hdparm“ and running „hdparm -d 1 /dev/hda“. If you want to test the speeds that you're getting, run „hdparm -T -t /dev/hda“ before and after the change.
To make it permanent you'll have to put the hdparm command in your startup scripts
/etc/rc.d/rc.local