Very Computer

[snipped]
 CP> Hardware: Celeron500, 128 Mb Samsung 15.3Gb UDMA mode4 HDD, SiS5513 IDE
 CP>           controller.
 CP> Kernel  : 2.2.16, patched with ide-2.2.16.20000630
 CP> BIOS    : Detects the harddisk as PIO4 and UDMA4
 CP> hdparm  : 3.9-1, params: -d1 -m16 -c1 -A1 (even tried -X66)
 CP>           (for some reason, after installing 3.9-1 my hdparm
 CP>           manpages were gone)

 CP> Enabled SiS5513 support in the kernel (yes, and even recompiled and
 CP> installed the new kernel :) ).

 CP> hdparm -t /dev/hda gives me on average  8Mb/s (slow!)
 CP> hdparm -T /dev/hda gives me on average 17Mb/s (waaaaaaay to slow!)

 CP> I've tried all I can think off, but it won't go any faster...

 CP> Anyone has any ideas?

Add -a1 and -u1 to your hdparm command line and benchmark again.

Regards,
  Neal