oflag=direct speed boost

[Dominik Smogór]

Hello,
Recently I have been playing with newewst dd version and noticed that "direct" 
flag gives huge speed boost ( 2x-3x) when accessing raw hdd.
I attributed it to bufer layer cpu overhead but on 10x faster CPU boost is the 
same. What is more, on head movement heavy IO load (dd'ing beeteween 
different disk places) transfer is also 2x faster.

What is the problem with my system. Is my system badly misconfigured?

Best regards,
DS.

ps
Please cc to address@hidden, thanks.


 dd if=/dev/hdc of=/dev/null bs=1M count=100 skip=600
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 7.10541 seconds, 14.8 MB/s

dd if=/dev/hdc of=/dev/null bs=1M count=100 skip=600 iflag=direct
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 2.87005 seconds, 36.5 MB/s

dd if=/dev/hdc of=/dev/null bs=1M count=100 skip=600 iflag=direct
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 2.69986 seconds, 38.8 MB/s