/dev/nvram does not exit

hi,
    i am new to this thing so please bear with me.  I am trying to
determine the free space in my CMOS memory.  What i did was
    cat /dev/nvram > /tmp/temp
i tried editting/replacing a single character with another character
in temp and write it back by
    cat /tmp/temp > /dev/nvram
my problem is, this command does not exit no matter how long i wait.
i have to press Ctrl-C to terminate it.  i tried
    cat /dev/nvram > /tmp/temp
    cat /tmp/temp > /dev/nvram
without editting any characters in temp and the command exits
immediately.  what happened?  what did i do?  please help.  any inputs
are very much welcome.

nick_faye