Linux has a slightly larger memory footprint than most conventional
embedded operating systems when configured with equivalent options.
This is the price you pay to leverage the advantages of its enormous
desktop user base, and being able to share a common desktop and
embedded environment. For most applications the difference is insignificant,
but if every last byte counts in your application, you might want to
consider 21.2. RTEMS - Real Time Executive for Multiprocessor Systems
or 21.1. eCos - Embedded Configurable Operating System
Beware that commercial embedded operating system vendors often make
meaningless claims regarding the footprint of their micro-kernel,
and the total memory footprint (and often the royalties payable)
increases substantially once all the optional packages needed to
provide the required functionality for a typical networked device
are included. Work out what functionality you need before attempting
to make valid comparisons.
For good architectural reasons, Linux isn't a micro-kernel. However,
it does allow large chunks of code to be removed easily at configuration
time. In practice the architectural distinction between micro and
monolithic kernels makes little difference to total memory requirements
of the overall system.
Minimum memory requirement when using an
root file system
is generally 2 MB of flash ROM and 8 MB of RAM, and here's what you
can expect to fit in:
This is the most common configuration because it attempts to minimize
ROM space at the expense of RAM, since ROM is generally more expensive.
However, you can trade off ROM space to reduce RAM usage by using a
compressed flash file system and/or running the kernel directly from ROM.
Both these options are more difficult, but have been successfully deployed
and discussed on the linuxppc-embeddedmailinglist