hdparm - настройка диска

вобщем под ядром 2.4.29, включенным со слакой 10.1 - скорость харда

/dev/hda:
 Timing cached reads:   756 MB in  2.00 seconds = 378.00 MB/sec
 Timing buffered disk reads:  166 MB in  3.01 seconds =  55.15 MB/sec
  
вот что выводит hdparm /dev/hda:
  
/dev/hda:
 multcount    = 16 (on)
 IO_support   =  1 (32-bit)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 9729/255/63, sectors = 80026361856, start = 0

         
а под скомпиленым ядром 2.6.11.12:

/dev/hda:
 Timing cached reads:   692 MB in  2.00 seconds = 345.53 MB/sec
 Timing buffered disk reads:   92 MB in  3.02 seconds =  30.42 MB/sec

bash-3.00# hdparm /dev/hda1

 multcount    = 16 (on)
 IO_support   =  1 (32-bit)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 16383/255/63, sectors = 10487199744, start = 63


Те почти в 2 раза скорость во втором случае меньше из-за чего?