excerpt from 'man bootparm';
NAME
       bootparam - Introduction to boot time parameters of the Linux kernel

DESCRIPTION
       The  Linux kernel accepts certain 'command-line options' or 'boot time parameters' at the moment it is started.  In general this is used
       to supply the kernel with information about hardware parameters that the kernel would not be  able  to  determine  on  its  own,  or  to
       avoid/override the values that the kernel would otherwise detect.

       When  the kernel is booted directly by the BIOS (say from a floppy to which you copied a kernel using 'cp zImage /dev/fd0'), you have no
       opportunity to specify any parameters.  So, in order to take advantage of this possibility you have to use software that is able to pass
       parameters, like LILO or loadlin.  For a few parameters one can also modify the kernel image itself, using rdev, see rdev(8) for further
       details.

       The LILO program (LInux LOader) written by Werner Almesberger is the most commonly used.  It has the ability to  boot  various  kernels,
       and  stores  the configuration information in a plain text file.  (See lilo(8) and lilo.conf(5).)  LILO can boot DOS, OS/2, Linux, Free-
       BSD, UnixWare, etc., and is quite flexible.

       The other commonly used Linux loader is 'LoadLin' which is a DOS program that has the capability to launch a Linux kernel from  the  DOS
       prompt (with boot-args) assuming that certain resources are available.  This is good for people that want to launch Linux from DOS.

       It  is  also very useful if you have certain hardware which relies on the supplied DOS driver to put the hardware into a known state.  A
       common example is 'SoundBlaster Compatible' sound cards that require the DOS driver to twiddle a few mystical registers to put the  card
       into  a  SB  compatible  mode.  Booting DOS with the supplied driver, and then loading Linux from the DOS prompt with loadlin avoids the
       reset of the card that happens if one rebooted instead.

   The Argument List
       The kernel command line is parsed into a list of strings (boot arguments) separated by spaces.  Most of the boot args take the form of:

              name[=value_1][,value_2]...[,value_10]

       where 'name' is a unique keyword that is used to identify what part of the kernel the associated values (if any) are  to  be  given  to.
       Note  the  limit of 10 is real, as the present code only handles 10 comma separated parameters per keyword.  (However, you can reuse the
       same keyword with up to an additional 10 parameters in unusually complicated situations, assuming the setup function supports it.)
Most of the sorting goes on in linux/init/main.c.  First, the kernel checks to see if the argument  is  any  of  the  special  arguments
       'root=', 'nfsroot=', 'nfsaddrs=', 'ro', 'rw', 'debug' or 'init'.  The meaning of these special arguments is described below.

       Then  it walks a list of setup functions (contained in the bootsetups array) to see if the specified argument string (such as 'foo') has
       been associated with a setup function ('foo_setup()') for a particular device or part of the kernel.  If you passed the kernel the  line
       foo=3,4,5,6  then  the kernel would search the bootsetups array to see if 'foo' was registered.  If it was, then it would call the setup
       function associated with 'foo' (foo_setup()) and hand it the arguments 3, 4, 5 and 6 as given on the kernel command line.

       Anything of the form 'foo=bar' that is not accepted as a setup function as described above is then interpreted as an  environment  vari-
       able to be set.  A (useless?) example would be to use 'TERM=vt100' as a boot argument.

       Any  remaining  arguments  that  were not picked up by the kernel and were not interpreted as environment variables are then passed onto
       process one, which is usually the init program.  The most common argument that is passed to the init process is the word 'single'  which
       instructs init to boot the computer in single user mode, and not launch all the usual daemons.  Check the manual page for the version of
       init installed on your system to see what arguments it accepts.