Computer
Operating Systems
When
you turn on the power to a computer, the first program that
runs is usually a set of instructions kept in the computer's
read-only memory (ROM). This code examines the system hardware
to make sure everything is functioning properly. This power-on
self test (POST) checks the CPU, memory, and basic input-output
systems (BIOS) for errors and stores the result in a special
memory location. Once the POST has successfully completed,
the software loaded in ROM (sometimes called the BIOS or firmware)
will begin to activate the computer's disk drives. In most
modern computers, when the computer activates the hard disk
drive, it finds the first piece of the operating system: the
bootstrap loader.
The bootstrap
loader is a small program that has a single function: It loads
the operating system into memory and allows it to begin operation.
In the most basic form, the bootstrap loader sets up the small
driver programs that interface with and control the various
hardware subsystems of the computer. It sets up the divisions
of memory that hold the operating system, user information and
applications. It establishes the data structures that will hold
the myriad signals, flags and semaphores that are used to communicate
within and between the subsystems and applications of the computer.
Then it turns control of the computer over to the operating
system.
The operating system's tasks, in the most
general sense, fall into six categories:
Processor management
Memory management
Device management (I/O and Disk)
Storage management (File management)
Application interface
User interface
Types
of Operating Systems
Within
the broad family of operating systems, there are generally
four types, categorized based on the types of computers they
control and the sort of applications they support. The categories
are:
Real-time operating system (RTOS) - Real-time operating systems
are used to control machinery, scientific instruments and
industrial systems. An RTOS typically has very little user-interface
capability, and no end-user utilities, since the system will
be a "sealed box" when delivered for use. A very
important part of an RTOS is managing the resources of the
computer so that a particular operation executes in precisely
the same amount of time, every time it occurs. In a complex
machine, having a part move more quickly just because system
resources are available may be just as catastrophic as having
it not move at all because the system is busy.
Single-user,
single task - As the name implies, this operating system is
designed to manage the computer so that one user can effectively
do one thing at a time. The Palm OS for Palm handheld computers
is a good example of a modern single-user, single-task operating
system.
Single-user,
multi-tasking - This is the type of operating system most
people use on their desktop and laptop computers today. Microsoft's
Windows and Apple's MacOS platforms are both examples of operating
systems that will let a single user have several programs
in operation at the same time. For example, it's entirely
possible for a Windows user to be writing a note in a word
processor while downloading a file from the Internet while
printing the text of an e-mail message.
Multi-user
- A multi-user operating system allows many different users
to take advantage of the computer's resources simultaneously.
The operating system must make sure that the requirements
of the various users are balanced, and that each of the programs
they are using has sufficient and separate resources so that
a problem with one user doesn't affect the entire community
of users. Unix, VMS and mainframe operating systems, such
as MVS, are examples of multi-user operating systems.
It's important
to differentiate between multi-user operating systems and
single-user operating systems that support networking. Windows
2000 and Novell Netware can each support hundreds or thousands
of networked users, but the operating systems themselves aren't
true multi-user operating systems. The system administrator
is the only "user" for Windows 2000 or Netware.
The network support and all of the remote user logins the
network enables are, in the overall plan of the operating
system, a program being run by the administrative user.
With the
different types of operating systems in mind, it's time to
look at the basic functions provided by an operating system.
How
Operating System Works?
When you
turn on your computer, it's nice to think that you're in control.
There's the trusty computer mouse, which you can move anywhere
on the screen, summoning up your music library or Internet
browser at the slightest whim. Although it's easy to feel
like a director in front of your desktop or laptop, there's
a lot going on inside, and the real man behind the curtain
handling the necessary tasks is the operating system.
Most desktop or laptop PCs come pre-loaded with Microsoft
Windows. Macintosh computers come pre-loaded with Mac OS X.
Many corporate servers use the Linux or UNIX operating systems.
The operating system (OS) is the first thing loaded onto the
computer -- without the operating system, a computer is useless.
More recently,
operating systems have started to pop up in smaller computers
as well. If you like to tinker with electronic devices, you're
probably pleased that operating systems can now be found on
many of the devices we use every day, from cell phones to
wireless access points. The computers used in these little
devices have gotten so powerful that they can now actually
run an operating system and applications. The computer in
a typical modern cell phone is now more powerful than a desktop
computer from 20 years ago, so this progression makes sense
and is a natural development.
The purpose
of an operating system is to organize and control hardware
and software so that the device it lives in behaves in a flexible
but predictable way. In this article, we'll tell you what
a piece of software must do to be called an operating system,
show you how the operating system in your desktop computer
works and give you some examples of how to take control of
the other operating systems around you.
|
