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.