Linux Definitions, Concepts and Key Ideas

An operating system is made up of software instructions that lie between the computer hardware and the application software. At the center is the kernel, which functions to control processes, handles memory management, and manages software and hardware communications. Besides the kernel, an operating system also provides other basic services such as file systems, device drivers, user interfaces and system services.

UNIX was originally born in 1969 at Bell Labs, and grew and evolved through the years. In the early 1980s, AT&T began to market UNIX, and also distributed it free to universities. UNIX began to be used more and more throughout the world. As multiple ports of UNIX started appearing, AT&T standardized what the different ports had to be able to do to still be called UNIX. To that end, compliance with the Portable Operating System Interface for UNIX (POSIX) and the AT&T UNIX System V Interface Definition (SVID) defined whether an operating system was UNIX or not. Some of the major operating systems that are POSIX compliant, and thus UNIX, are Solaris, Linux, AIX, and HP-UX.

Linux is a free Unix-type operating system originally created by Linus Torvalds in August of 1991 when he was a student at the University of Helsinki. He wrote it partly from scratch and partly by using publicly available software. He then released it to the internet and asked others to work with it, fix it and enhance it. Developed under the GNU General Public License, the source code for Linux is freely available to everyone. Although much of the code for Linux started from scratch, the blueprint for what the code would do was created to follow POSIX standards.

In general, ‘open source’ refers to any program whose source code is made freely available for use or modification. Open source software is usually developed as a public collaboration project and is made freely available, as are patches and fixes.

When Linus Torvalds first developed Linux, the operating system basically consisted of his kernel and some GNU tools. With the help of other developers, Linus added more and more tools and applications.

Clustering is most widely recognized as the ability to combine multiple systems in such a way that they provide services a single system could not. Clustering is used to achieve higher availability, scalability and easier management. Higher Availability can be achieved by use of "failover" clusters, in which resources can automatically move between 2 or more nodes in the event of a failure. Scalability can be achieved by balancing the load of an application across several computer systems. Simpler management can be attained through the use of virtual servers, as opposed to managing each individual computer system.

High availability clustering joins together two or more servers to help ensure against system failures including planned shutdowns (e.g., maintenance, backups) and unplanned outages (e.g., system failure, software failure, operator errors). The group of connected systems is known as a cluster.

Beowulf or High Performance Computing Cluster (HPCC) combines multiple Symmetric Multi-Processor (SMP) computer systems together with high-speed interconnects to achieve the raw-computing power of classic "big-iron" supercomputers. These clusters work in tandem to complete a single request by dividing the work among the server nodes, reassemble the results and present them to the client as if a single-system did the work.

Server farms that can distribute requests to the same application among multiple independent servers are referred to as "load balancing". The term load balancing applies to clusters that include some number of nodes processing requests for the same type of application, often web servers, streaming media servers, terminal servers, or read only FTP and file servers. There are software-based mechanisms to perform load balancing, as well as appliance-based mechanisms.

Scalable Clusters provide the freedom of adding compute nodes in a cluster in order to increase the joint resources of processing. This can add to the power of computation since processors within a cluster can communicate data more efficiently and hence it also can reduce the average memory access time. This is particularly attractive when running parallel applications.

Oracle RAC is a parallel database clustering technology from Oracle that runs under Linux and is an option of Oracle9i Enterprise Edition. RAC enables IT organizations to acquire key competitive advantages from a technical and business standpoint: