What is Unix and Linux ?

What is Unix and Linux ?

What is an operating system ?

An operating system is a system software who is responsible for direct inspection and management of computer hardware and running application programs. Operating systems enable all other software to access memory, I/O devices, etc.

Kernel can be considered as brain of an operating system. Existing of an operating system without a kernel is impossible. All the other programs communicate via kernel. Kernel gains value when it becomes together with other programs. It enables programs to communicate with hardware and other programs uniformly, which means independent from hardware and software.

One of the most interesting examples of operating systems is Debian GNU/Linux. Currently, Debian is composed of Linux kernel and GNU tools, but now it is being updated in such a way that it could run on Hurd kernel. Main purpose of the Debian team is to prepare an operating system which provides users the opportunity of running the same GNU tools on different kernel alternatives.

What is UNIX ?

In 60's and 70's, there were operating systems which are developed for a specific computer in assembly language. For every new computer system, a new operating system was being developed in order to make users benefit from computers in a more comfortable manner.

Only a little part of the UNIX was developed in assembly language. It was developed in late 60's. Major part of the operating system was developed in C language which is also developed in almost the same years. Developing an operating system in a high-level language like C compared to assembly, provided computer manufacturers with the mobility, which means moving UNIX in their computer systems. So, it was a major technological improvement.

Application programming interface (API) which is provided with UNIX, enabled all the applications to be developed without any problem on all UNIX systems. An application that is developed for one UNIX can be transferred to other UNIX systems using re-compiling without any problem.

Properties of UNIX

Multi-tasking

It is the ability of running more than one task concurrently. Multiple tasks can be run in parallel if there are multiple CPU's or they can be run as if they are parallel if there is one CPU. For example, while working with a word processor like WPS Writer, it is possible to back-up the disk.

Multi-user

It means multiple users can use a computer system concurrently. For example, while a user is watching a movie, other one can surf on the web.

Time Sharing

Thanks to this feature, all the jobs on the system can be maintained even if a computer has only a single CPU. Every user has a priority on the system and the time taken  from CPU to processes for those users is assigned according to those priorities. Super user can change the priority of the users and tasks.

Portability

It is the ability to move to a computer system with a different architecture with only a little change in the code. This broad compatibility allows architecture dependency to be reduced and variety to be increased.

High Performance

In the UNIX world which simplicity is preferred over visuality, many applications can be run with a better performance. Even though it is an operating system that is developed in the early 70's it is preferred by most companies on critical duties.

What is Linux ?

Linux is manifested as a result of experiments of a second year student at University of Finland, whose name is Linus Torvalds. He has done his work on a computer system based on a Intel 80386 architecture. Linux has tried to make his computer to open without an operating system and make it run applications. 0.02 version which is the first product of Linus is completed in 1991. Linus has attended a lecture whose topic was MINIX and he decided to create a better operating system than it. His message which is sent to internet groups, attracted a lot of attention and gained support. Volunteers who supported Linus and his project which is called 'Linux' has contributed it to become real.

Linux is distributed under GNU General Public License which enables its source code to belong everyone and open to every person. Linux is only a kernel of an operating system and it becomes meaningful with other free software which makes it useful.

Message from Linus

From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
Newsgroups: comp.os.minix
Subject: What would you like to see most in minix?
Summary: small poll for my new operating system
Message-ID: <1991Aug25.205708.9541@klaava.Helsinki.FI
Date: 25 Aug 91 20:57:08 GMT
Organization: University of Helsinki
Hello everybody out there using minix -
I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones. This has been brewing
since april, and is starting to get ready. I'd like any feedback on things people like/dislike in minix, as my OS resembles it somewhat (same
physical layout of the file-system (due to practical reasons) among other things). I've currently ported bash(1.08) and gcc(1.40),and
things seem to work.This implies that I'll get something practical within a few months, andI'd like to know what features most people would
want.
Any suggestions are welcome, but I won't promise I'll implement them :-)
Linus (torvalds@kruuna.helsinki.fi)
PS. Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT protable (uses 386 task switching etc), and it probably never will
support anything other than AT-harddisks, as that's all I have :-(

Properties of Linux

The most important feature of Linux is it belongs to public. Corporations that want to use Linux don't have to pay any license fees. Even if people and companies who contributed to development of Linux give up some day, other volunteers can continue developing it as long as it belongs to public. That way, dangers like producer changing the strategy, end the product or offering severe conditions after creating a product dependency are eliminated.

Source code of the system is open for anyone who wants to view and modify. Any person who wants to view, download, modify or distribute the modified version can reach the source code from here. Because of source code is open like this, it is very easy to trace and find the bugs. If we think there are thousands of people viewing the source code, we can understand how easy it is to find a bug in the code.

Another advantage of having the source code open is that new features can easily be added and the corporations can meet their unique expectations.

Apart from the addition of the new feature, the system can be shaped according to the sub-level settings and it is possible to disable unnecessary parts. Thus, a system suitable for the job can be obtained.

Linux can be run on different hardware platforms like HP-Compaq Alpha, Sun Sparc ve UltraSparc, Motorola PowerPC and StrongARM in the same way. An application that is running on a specific architecture can be moved to another Linux without any problems.  For example, if the server used for Intel Pentium architecture is insufficient a migration is possible to an IBM with many PowerPC processors, or a Sun computer system with a number of UltraSparc processors. Re-compilation of applications on new architectures is enough for this process.

Linux is in great harmony with other UNIX variants. Linux environment which has the features of both AT&T and BSD, has the ability to run other UNIX applications on itself. In this case, for example, an application developed on Sun Solaris systems can be re-compiled and run on Linux almost without change.

Linux Distributions

The software, which basically uses the Linux kernel and is bundled with the kernel, is called the Linux distribution as a whole. There are many companies and / or non-governmental organizations that prepare paid and free Linux distributions. 


Distributions can be used to make changes to the settings of the Linux kernel,
applying custom patches with preferences, and putting different free software into the distribution package. To differentiate, placing commercial licensed applications in the package, offering paid technical support and putting local language support at the forefront is another way to go.

RedHat, Ubuntu, Suse, Debian GNU / Linux and TurboLinux are Linux distributions, all showing differences with the qualities summarized in the previous paragraphs, despite having the same kernel (Linux) at the core.