Flexibility - The source code to the Linux kernel is copylefted under the GNU Public License , meaning that the system must be freely distributed with source code available, and anyone may freely modify that source code provided that any modifications they distribute are distributed with source code. Because the source to Linux is open, it is easy to customize. This flexibility has enabled Linux to run on everything from hand-helds and embedded systems to clusters of hundreds of servers and mainframes. Because the source code to Linux is open and widely distributed, Linux has been thoroughly debugged. Linux's fundamental architecture also creates a more reliable system.
Systems using protected memory and preemptive multitasking are inherently more stable.
Protected memory prevents an error in one application from bringing down the entire system, and genuine multitasking means that a bottleneck in one application does not hold up the rest of the system. Linux also maintains a clean separation between user processes and kernel processes. While other server class operating systems use protected memory, protected memory does no good if faulty applications are allowed to invade kernel space with their processes. Because Linux is open source, the initial cost is low. There are no seat licenses, and no usage fees associated with the operating system.