Programs To Access System Resources

3.6    OTHER OPERATING SYSTEMS
There have been many operating system that were significant in their day but are no longer so, such as AmigaOS; OS/2 from IBM and Microsoft; Mac OS, non-Unix precursor to Apple Mac OS X; BeOS; XTS-300; RISC OS; MorphOS; Haiku; BareMetal and FreeMint. Some are still niche markets and continue to be develop as minority platform for enthusiast communities and specialist application. OpenVMS, formally from DEC, is still under active development by Hewlett-packard. Yet other operating system are used almost exclusively in academia, for operating system application or to do research on operating system concepts. A typical example of system that fulfils both roles is Minix, while for example singularity is used purely for research.
Other operating system failed to win significant market share but have introduce innovation that have influenced mainstream operating system not least Bell Labs’ plan.
3.7    LINUX HAS ALL OF THE COMPONENTS OF A TYPICAL OS
a)    Kernel: The Linux Kernel includes device drivers supports for a large number of PC hardware devices (graphics card, network cards, hard disk etc.) advanced processor and memory management features, and support for many different types of file systems (including DOS floppies and the ISO9660 standard for CD ROMs). In terms of the services that it provides to applications programs and file utilities, the Kernel implements most BSD and SYSV system calls, as well as the system calls described in the POSIX.1 specification.
The Kernel (in raw binary form that is loaded directly into memory at system start up time) is typically found in the file/ boot/vmLinuz, while the source files can usually be found/usr/src/linux.
b)    Shells and GUIs: Linux support two forms of command input: through textual command line shells similar to those found in most UNIX system (e.g., sh – the Bourne shell, bash- the Bourne again shell and csh – the C shell) and through graphical interface (GUIs) such as the KDE and GNOME window managers. If you are connecting remotely to a server your access will typically be through a command line shell.
c)    System Utility: virtually every system Utility that you would expect to find on standard implementation of UNIX (including every system utility described in the POSIX.2 specification) has been ported to Linux. This includes commands such as Is, Cp, Grep, Awk, Sed, Bc, Wc, more, and so on. These system utility are designed to be powerful tools that do a single task extremely well (e.g., grep finds text inside files while WC counts the numbers of words, lines and bytes inside a file). Users can often solve problem by interconnecting these tools instead of writing a large monolithic application program. Like other UNIX flavors, Linux’s system utility also include server program called Daemons which provides remote network administration services (e.g., telnetd and sshd provide remote login facilities, ipd provides printing services, httpd serves web page, crond runs regular system administration tasks automatically). A Daemon (probably derived from the Latin word which refers to a beneficent spirit who watches over someone, or perhaps short form “Disk and Execution monitor”) is usually spawned automatically at system start up and spend most of its time lying dormant (lurking?) waiting for some event to occur.
d)    Application programs: Linux distributions typically comes with several useful application program as standard. Examples includes the emacs editor, xv (an image viewer), gcc (a C compiler) g++ (a C++ compiler), xfig (a drawing package), Latex (powerful typesetting language) and suffice (starOffice, which is an MS- Office style clone that can read and write word, excel and PowerPoint files)
Redhat Linux also comes with rpm, the Redhwat package manager which makes it easy to install and uninstall application program.