If you say Y here and create a character special file /dev/nvram
with major number 10 and minor number 144 using mknod ("man mknod"),
you get read and write access to the non-volatile memory.

/dev/nvram may be used to view settings in NVRAM or to change them
(with some utility). It could also be used to frequently
save a few bits of very important data that may not be lost over
power-off and for which writing to disk is too insecure. Note
however that most NVRAM space in a PC belongs to the BIOS and you
should NEVER idly tamper with it. See Ralf Brown's interrupt list
for a guide to the use of CMOS bytes by your BIOS.

This memory is conventionally called "NVRAM" on PowerPC machines,
"CMOS RAM" on PCs, "NVRAM" on Ataris and "PRAM" on Macintoshes.

To compile this driver as a module, choose M here: the
module will be called nvram.

source code:

drivers/char/nvram.c