Monolithic kernels

A relatively large kernel with sophisticated capabilities is adapted
to suit an embedded environment. This gives programmers an environment
similar to a desktop operating system like Linux or Microsoft Windows,
and is therefore very productive for development; on the downside, it
requires considerably more hardware resources, is often more
expensive, and because of the complexity of these kernels can be less
predictable and reliable.

Common examples of embedded monolithic kernels are Embedded Linux and
Windows CE.

Despite the increased cost in hardware, this type of embedded system
is increasing in popularity, especially on the more powerful embedded
devices such as Wireless Routers and GPS Navigation Systems. Here are
some of the reasons:

* Ports to common embedded chip sets are available.

* They permit re-use of publicly available code for Device
Drivers, Web Servers, Firewalls, and other code.

* Development systems can start out with broad feature-sets, and
then the distribution can be configured to exclude unneeded
functionality, and save the expense of the memory that it would
consume.

* Many engineers believe that running application code in user
mode is more reliable, easier to debug and that therefore the
development process is easier and the code more portable.

* Many embedded systems lack the tight real time requirements of a
control system. A system such as Embedded Linux has fast enough
response for many applications.

* Features requiring faster response than can be guaranteed can
often be placed in hardware.

* Many RTOS systems have a per-unit cost. When used on a product
that is or will become a commodity, that cost is significant