LINUX

What is Linux?

Linux is a free operating system. The name "Linux" actually refers to the kernel (core of an operating system) of a unix-alike operating system (Derivat). But this term is often used for the complete operating system (Distribution). Besides the programs essential to the operating system, e.g. for file and user administration, it also covers graphical frontends, office applications, multimedia tools, databases, web browser and other programs. Linux is free, that means the sources are open, so that the system can be adapted to the respective application. It is free to copy and there are no fees for software licensing. Furthermore Linux is multisupplier.

History

1969 - Ken Thompson (Bell Labs) writes the 'Original-UNIX' in Assembler
1978 - UNIX Version 7 as a commercial product (in C) Many well-known manufacturer license UNIX and transfer it onto their hardware
1979 - first official AT&T-Version System III
1984 - AT&T-Version System V
1989 - AT&T-Version System V.4 (in close cooperation with Sun)
1991 - on September 17th 1991 Linus Torvalds publishes the result of his studies in regards to a Unix-related operating system within the newsgroup 'Minix'. In this start-up version was just a rudimental kernel implemeted. Linus calls for more code contributions, which he would then distribute. The Linux-Code has soon replaced Minix completely. Further computer programs like Apache, Samba, Python and Bind are generated this way.
1998 -IBM supports the Apache Web Server. Sun Microsystems and Adaptec enter Linux International. Oracle and Informix transfer their databases to Linux. In the Helloween-Documentation Microsoft points out the advantages of Open Source programs and classifies them as serious competition for the Microsoft-products.

The tasks of the operating system

The operating system is the 'Interface to the hardware' and has to perform various administrative and controlling services.

One can divide these tasks into 7 function units. The operating system contains the data management, the safety, the communication as well as the user interface. Furthermore the development tools, the logging and the time sharing are counted among those units:

Data Management

Linux manages the access to the memory provided by the disk. The management of the memory disk is performed by a data system in case of secondary memory. Linux groups a certain number of units together in so called cluster. These are the smallest adressable memory units. Furthermore Linux provides data systems. Each data system has its own allocation tables. The operating is also responsible for the (de)fragmentation of the memory and therefore for the provision of coherent memory space.

Safety

Linux is a multiuser- multitasking-system that is suitable for single seat computer. Multitasking is the ability to manage and/or execute multiple programs (tasks) at the same time. Therefore Linux offers various procedures for the security of data. Each user has to be authenticated and his/her autorisation is reviewed. Each user has clearly defined rights. The system also stores for each file a number of administrative data. Access rights are associated with each file.

Communication

Under this headline are programs combined that allow a user to exchange data with another computer and/or another user or even have direct access to a remote computer.

User Interface

User Interfaces are programs that enable the user to communicate his/her instructions to the operating system. These commands can be text or graphic oriented. These programs are usually also responsible for the return of results as requested by the used command.

Development Tools

Development Tools refer to programs which allow the programmer to create applications with the system. Editors, coding environments, compiler and program binder are examples of this group of programs.

Logging

Linux offers the possibility to track the activities of users. It can be recorded how long a user was logged into the system, how much computing time he/she needed and what kind of traffic he/she generated in the network.

Time Sharing

Because multiple users and/or processes share common ressources, e.g. the CPU, Linux possesses implented mechanisms that make sure that the processor is assigned alternatingly to the various tasks. The assignment of the processor to the processes is carried out by so-called time disks. Each process disposes of the CPU for a certain time span, is then suspended and another process is executed. The calculation and the assignment of the CPU-time is done by the so-called Scheduler-Process. The switching of the processes is executed by the Dispatcher.

Linux Architecture

In the uppermost layer we find the application programs. Strictly speaking they do not belong to the operating system but are separate programs. Underneath are the service programs of the system. It is a collection of programs, e.g. text editors or command interpreters. These programs are usually written in C and are a fixed part of the operating system.

The kernel is the most important part of the system. When the computer is started, he is loaded into the working memory. He is responsible for the device management and control. Also the process controlling, the interprocess communication and the timing is covered by the kernel.

The service and application programs transmit commands with the help of system calls to the kernel. The kernel is for the most part (over 90 %) written in C. Only the direct device control and some time critical parts of the kernel are designed in Assembler.