The Exokernel Operating System and Active Networks - Advanced Operating Systems and Kernel Applications - page 140

code optimization and who is best suited for this
task. We will concede that some processes - like
multithreaded applications - perform worse in an
Ekokernel environment. We will finally question
if extensibility is even the solution to the grow-
ing problem of operating systems becoming the
bottleneck of computer system performance. We
will conclude that despite some of the issues that
make the Exokernel commercially unacceptable at
this time, the Exokernel's enhancements outweigh
its shortcomings and therefore we encourage the
reader to embrace its approach.

into the operating system, then these items must
also be considered to be part of the definition of
an operating system.
Regardless of which definition of an operating
system you agree with, we must all agree that the
traditional operating system is that program that
abstracts the hardware and offers the user a single
interface with which to interact with. It is this
single interface approach that has the traditional
operating system literally caught in the middle
between two different forces. One force is the
need for a more flexible operating system. As 64
bit processors replace 32 bit processors, the need
for an operating system that can interact with this
new hardware has grown. Larger memory de-
vices - such as hard drives that are now measured
in terrabytes - as well as fiber-optic networks,
high-bandwidth networks, and new data storage
devices, have also demanded a more flexible
operating system.
In addition to the flexibility demands being
made by hardware, software applications are also
demanding a more flexible operating system to
meet their needs. For example, realistic gaming
programs are requiring access to hardware in
non-traditional ways. Portable computing and
communication devices are requiring the ability to
up-load and down-load data more easily. Database
systems want to be able to access memory in their
own ways, and real-time systems demand a spe-
cific performance level that can be best achieved
through a flexible operating system. All of these
have combined into one force that is demanding
the traditional operating system become more
flexible to change.
The traditional operating system could be
pulled-apart by these forces if it continues to re-
main rigid in its design. Therefore, the traditional
operating system needs a more flexible design.

problem deScription

The need for a new operating system design has
been motivated by two forces - the need for speed
and the need for flexibility. These two forces are
explained next.

the need for flexibility

Trying to define the term “operating system” is an
ongoing debate. Some say the operating system
is simply that software program that sits between
the hardware and the other user programs. It is
that program that provides a simple interface that
allows processes to interact with the hardware.
Others say the operating system is the manager
and protector of computer resources. It manages
how every computer resource gets used and also
protects the resources against improper use.
Some have argued that an operating system is
defined by the manufacturer. As was stated previ-
ously, an operating system is “whatever comes in
the box when it is purchased” (Leschke, 2004).
This means that if a user-manual is included in
the package, then the user-manual is a formal part
of the operating system. Furthermore, whatever
software is bundled-with or integrated-with the
operating system is also a part of the operating
system. For example, if a text editor or an entire
suite of office application software is integrated

the need for Speed

Gene Amdahl has provided us with “Amdahl's
Law” - one of the fundamental laws of computer