properly, the most important processes get the quickest responses from the processor. For
example, a Linux scheduler on a desktop system gives higher priority to things such as
moving a window on the desktop than it does to a background file transfer.
Memory -- Linux tries to keep processes with the most immediate need in RAM, while
managing how processes that exceed the available memory are moved to swap space.
Swap space is a defined area on your hard disk that's used to handle the overflow of
running processes and data. When RAM is full, processes are placed in swap space.
When swap space is full (something that you don't want to happen), new processes
can't start up.
Devices -- Linux supports thousands of hardware devices, yet keeps the kernel a man-
ageable size by including only a small set of drivers in the active kernel. Using loadable
modules, the kernel can add support for other hardware as needed. Modules can be
loaded and unloaded on demand, as hardware is added and removed. (The kernel,
described in detail a bit later on, is the heart of a Linux operating system.)
File systems -- File systems provide the structure in which files are stored on hard disk,
CD, DVD, floppy disks, or other media. Linux knows about different file system types
(such as Linux ext3 and reiserfs file systems, or VFAT and NTFS from Windows systems)
and how to manage them.
Security -- Like UNIX, Linux was built from the ground up to enable multiple users to
access the system simultaneously. To protect each user's resources, every file, directory,
and application is assigned sets of read, write, and execute permissions that define who
can access them. In a standard Linux system, the root user has access to the entire system,
some special logins have access to control particular services (such as Apache for Web
services), and users can be assigned permission individually or in groups. Recent features
such as Security Enhanced Linux and AppArmor enable more refined tuning and protec-
tion in highly secure computing environments.
What I have just described are components that are primarily managed by what is referred to as
the Linux kernel. In fact, the Linux kernel (which was created and is still maintained by Linus
Torvalds) is what gives Linux its name. The kernel is the software that starts up when you boot
your computer and interfaces with the programs you use so they can communicate effectively and
simply with your computer hardware.
Components such as administrative commands and applications from other free and open source
software projects work with the kernel to make Linux a complete operating system. The GNU
Project, in particular, contributed many implementations of standard UNIX components that are
now in Linux. Apache, KDE, GNOME, and other major open source projects in Linux, discussed a
bit later, have also contributed to the success of Linux. Those other projects added such things as:
Graphical user interfaces (GUIs) -- Consisting of a graphical framework (typically the
X Window System), window managers, panels, icons, and menus. GUIs enable you to
use Linux with a keyboard and mouse combination, instead of just typing commands
(as was done in the old days).
7
Starting with Linux
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