What is Linux? Linux is a clone of the operating system UnIX, written from scratch by LinusTorvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UnIX Specification compliance.
It has all the features you would expect in a modern fully-fledged Unix, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and Tcp/IP networking.
Linux was first developed for 32-bit x86-based PCs (386 or higher). These days it also runs on (at least) the Compaq AlphaAXP, SunSPARC and UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 and CRIS architectures.
Linux is easily portable to most general-purpose 32- or 64-bit architectures as long as they have a paged memory management unit (PMMU) and a port of the GNU C compiler (gcc).