Linux is free.
You can install a complete Unix system at no expense other than the hardware (of course).
Linux is fully customizable in all its components.
Thanks to the General Public License (GPL), you are allowed to freely read and Modify the source code of the kernel and all system programs.
Linux runs on low-end, cheap hardware platforms.
You can even build a network server using an old Intel 80386 system with 4 MB of RAM.
Linux is powerful.
Linux systems are very fast, since they fully exploit the features of the hardware components. The main Linux target is efficiency, and indeed many design choices of commercial variants, like the STREAMS I/O subsystem, have been rejected by Linus because of their implied performance penalty.
Linux has a high standard for source code quality.
Linux systems are usually very stable; they have a very low failure rate and system maintenance time.
The Linux kernel can be very small and compact.
Indeed, it is possible to fit both a kernel image and full root filesystem, including all fundamental system programs, on just one 1.4 MB floppy disk! As far as we know, none of the commercial Unix variants is able to boot from a single floppy disk.
Linux is highly compatible with many common operating systems.
It lets you directly mount filesystems for all versions of MS-DOS and MS Windows, SVR4, OS/2, Mac OS, Solaris, SunOS, NeXTSTEP, many BSD variants, and so on. Linux is also able to operate with many network layers like Ethernet, Fiber Distributed Data Interface (FDDI), High Performance Parallel Interface (HIPPI), IBM's Token Ring, AT&T WaveLAN, DEC RoamAbout DS, and so forth. By using suitable libraries, Linux systems are even able to directly run programs written for other operating systems. For example, Linux is able to execute applications written for MS-DOS, MS Windows, SVR3 and R4, 4.4BSD, SCO Unix, XENIX, and others on the Intel 80x86 platform.
Linux is well supported.
Believe it or not, it may be a lot easier to get patches and updates for Linux than for any proprietary operating system! The answer to a problem often comes back within a few hours after sending a message to some newsgroup or mailing list. Moreover, drivers for Linux are usually available a few weeks after new hardware products have been introduced on the market. By contrast, hardware manufacturers release device drivers for only a few commercial operating systems, usually the Microsoft ones.
Therefore, all commercial Unix variants run on a restricted subset of hardware components.
With an estimated installed base of more than 12 million and growing, people who are used to certain creature features that are standard under other operating systems are starting to expect the same from Linux. As such, the demand on Linux developers is also increasing. Luckily, though, Linux has evolved under the close direction of Linus over the years, to accommodate the needs of the masses
Linux tries to maintain a neat distinction between hardware-dependent and hardware-independent source code. To that end, both the arch and the include directories include nine subdirectories corresponding to the nine hardware platforms supported. The standard names of the platforms are:
arm alpha i386 m68k mips ppc sparc sparc64 s390
Acorn personal computers
Compaq Alpha workstations
IBM-compatible personal computers based on Intel 80x86 or Intel 80x86-compatible microprocessors
Personal computers based on Motorola MC680x0 microprocessors
Workstations based on Silicon Graphics MIPS microprocessors
Workstations based on Motorola-IBM PowerPC microprocessors
Workstations based on Sun Microsystems SPARC microprocessors
Workstations based on Sun Microsystems 64-bit Ultra SPARC microprocessors
IBM System/390 mainframes