I have installed Knoppix on my Hard Drive, and the hard drive goes really slow:

root@Walkyria:/home/Antonio# hdparm -Tt /dev/hdc

/dev/hdc:
Timing cached reads: 3112 MB in 2.00 seconds = 1553.91 MB/sec
Timing buffered disk reads: 4 MB in 4.41 seconds = 928.10 kB/sec


And I realize i havent DMA enabled. But when i try to enable it, something is wrong:

root@Walkyria:/home/Antonio# hdparm /dev/hdc

/dev/hdc:
multcount = 16 (on)
IO_support = 0 (default 16-bit)
unmaskirq = 0 (off)
using_dma = 0 (off)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 16383/255/63, sectors = 117210240, start = 0

root@Walkyria:/home/Antonio# hdparm -d1 /dev/hdc

/dev/hdc:
setting using_dma to 1 (on)
HDIO_SET_DMA failed: Operation not permitted
using_dma = 0 (off)


I installed from knoppix 4.0.2 . The Kernel has activated the options Generic PCI IDE chipset support and Generic PCI bus-master DMA support
I have tried to change /etc/hdparm.conf, and added a line like:

/dev/hdc {

write_cache = on
dma = on
}

But doesnt work.
However, during boot, appears the message: "Enabling DMA acceleration for: hdc". I cant understand what happens.

Can anyone help me?