dd performance

[chefren]

Wiping identical 18GB SCSI disks on same Dell 1750 machine:

OpenBSD 3.8:

dd if=/dev/zero of=/dev/sd0c bs=1024k

6MB/s


Linux 2.4:

dd if=/dev/zero of=/dev/sda bs=1024k

53MB/S



Any clue about the difference? Of course I'm also interested in 
different ways to do this but the difference is what puzzles me.

+++chefren