Chapter 1<P> What determines performance
What determines performance
A computer system consists of a finite set of hardware and
software components. These components constitute the
resources
of the system.
One of the tasks of the operating system is
to share these resources between the programs that are
running on the system.
Performance is a measure of how well the operating system does this
task; the aim of performance tuning is to make it do this task better.
A system's hardware resources have inherent physical limits
in the quantity of data they can handle and the speed with which
they can do this. The physical subsystems that compose hardware include:
One or more central processing units (CPUs),
and the ancillary processors that support them.
Memory -- both in Random Access Memory (RAM)
and as
swap space
on disk.
I/O
devices including hard and floppy disk drives,
tape drives, serial ports, and network cards.
Networks -- both Local Area Networks
(LANs) and Wide Area Networks (WANs).
Operating system resources are limited by the hardware resources
such as the amount of memory available and how it is accessed.
The internal resources of the operating system are usually
configurable and control such things as the size of data
structures, security policy, standards conformance, and
hardware modes.
Examples of operating system resources are:
The tables that the operating system uses to keep track
of users and the programs they are running.
The buffer cache and other memory buffers that
reduce dependence on accessing slow peripheral devices.
If your system is connected to one or more networks, it may
depend on remote machines to serve files, perform database
transactions, perform calculations, run X clients, and
provide swap space, or it may itself provide some of these services.
Your system may be a router or gateway if it is connected to more
than one network. In such cases, the performance of the network
and the remote machines will have a direct influence on the
performance of your system.