Knoppix 4.0.2 vs Mandrake: 20x slower PATA IDE HDD??

[dv440]

I have a Dell GX260 (Pentium 4) with plain-vanilla 7200RPM PATA IDE hard drive. Mandrake 10 is installed.

Under Mandrake 10, executing
# time dd if=/dev/zero of=/zero.bin bs=4K count=250000
creates a 1GB file on a ext3 partition. Time taken = 14.94 seconds, for a write throughput of 69 MB/sec.

Similarly, read throughput comes out 58 MB/sec, gauged via
# time dd if=/zero.bin of=/dev/null bs=4K

I now boot the same system with Knoppix 4.0.2. Mount (read-write) the exact same HDD partition as above.
Run exact same write and read commands as above.

Throughput under Knoppix 4: 2 MB/sec read, 3 MB/sec write.
Again, under Mandrake 10: 58 MB/sec read, 69 MB/sec write.

More data:
I repeated this experiment on the same PC but using a different IDE controller (PCI vs. motherboard) and got very similar results.
I repeated this experiment on a different PC (Biostar iDEQ - Athlon XP, again PATA 7200RPM HD) and got very similar results.

Summary: I get a factor of >20 reduction in IDE throughput using Knoppix 4.0.2 vs. Mandrake 10, with 3 different HW setups.

Could anyone offer any help as to why this would be? Thanks in advance.

[UnderScore]

Unless it has changed in 4.x & up ... http://www.knoppix.net/forum/viewtop...?p=82158#82158