The Operating System Linux

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3. Linux

3.1 Introduction:

The operating system Linux is an open source version of UNIX [6]. In 1992 [8] Linus Torvalds, who was a computer science student -at the University of Helsinki- [6], was the one who started this operating system.

Linux is used on variety of hardware (e.g. on workstations, mid-and high-end servers and on gadgets), which makes it unique [6]. Linux keeps maintaining its position in the market due to the hard work of both employees and volunteers [6].

Previously, UNIX systems used batch jobs, which run a process until it is finished and then the next process will run [8]. What UNIX used is known as “non-preemptive scheduling” [8]. After years, preemptive scheduling was used to run processes in parallel by switching between them [8].

3.2 Scheduling Technique: Linux scheduler is based on Time-Sharing Scheduling technique [7], which means “It can effectively schedule tasks that have strict timing requirements”. The CPU is divided into small sections, which allows many process to run simultaneously [7]. Time-sharing depends on “timer interrupts” [7].

3.2 Scheduling Priorities:

The priority ranges differ for real- time tasks and normal tasks in Linux scheduler [1]. In real-time tasks: priorities vary from 0 to 99. In normal tasks: processes’ priorities range from 100 to 139. Processes who have higher priorities are “numerically” lower than others [1].
Normal tasks are appointed priorities “based on their nice
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