Problems enabling DMA on /dev/cdrom with hdparm

[alan snyder att net]

I am running RedHat 8.0 on a Dell Dimension Desktop 8200 with a DVD-ROM drive as
my /dev/hdc (/dev/cdrom) device. Whenever I try to run the command below on my
cdrom, also /dev/hdc, I get the following...

[root localhost sbin]# ./hdparm -d1 /dev/cdrom

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

I get the exact same message when I do this command on /dev/hdc as well...

[root localhost sbin]# ./hdparm -d1 /dev/hdc

/dev/hdc:
 setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Operation not permitted
 using_dma    =  0 (off)
[root localhost sbin]#

I am logged into KDE as 'alan', then I do 'su' to root in a bash shell. When I
execute the command above, I get the message 'Operation not permitted'. I don't
quite understand why because I'm logged in as root. 

Any thoughts??
Thanks in advance -- Alan