What is Linux ?

Linux is a completely free reimplementation of the POSIX specification, with SYSV and BSD extensions, and it's available in both source code and binary form. It was originaly developed as a hobby project by Linus Torvalds and is freely redistributable under the terms of the GNU Public License.

Linux is freeware, and you may give copies away, but you must also give the source with it or make it available in the same way. If you distribute any modifications, you are legally bound to distribute the source for those modifications. See the GNU General Public License for details.

Linux runs on multiple platforms :

• On 386/486/Pentium machines with ISA, EISA, PCI and VLB busses.
• On Motorola 680x0 platforms.It requires a 68020 with an MMU, a 68030, 68040, or a 68060, and also requires an FPU.
• On DEC's Alpha CPU.
• On Sun SPARCs; most sun4c and sun4m machines now run Linux, with support for sun4u in active development.
• On PowerPC architecture, including PowerMac (Nubus and PCI), Motorola, IBM, and Be machines.

Linux Features :

• Multitasking: several programs running at once.
• Multiuser: several users on the same machine at once.
• Multiplatform: runs on many different CPUs.
• Multiprocessor: SMP support is available on the Intel and SPARC platforms.
• Runs in protected mode on the 386.
• Has memory protection between processes, so that one program can't bring the whole system down.
• Demand loads executables: Linux only reads from disk those parts of a program that are actually used.
• Shared copy-on-write pages among executables. This means that multiple process can use the same memory to run in.
• Virtual memory using paging to disk: to a separate partition or a file in the filesystem, or both, with the possibility of adding more swapping areas during runtime.
• A unified memory pool for user programs and disk cache, so that all free memory can be used for caching, and the cache can be reduced when running large programs.
• Dynamically linked shared libraries (DLL's), and static libraries too, of course.
• Does core dumps for post-mortem analysis, allowing the use of a debugger on a program not only while it is running but also after it has crashed.
• Mostly compatible with POSIX, System V, and BSD at the source level.
• Through an iBCS2-compliant emulation module, mostly compatible with SCO, SVR3, and SVR4 at the binary level.
• All source code is available, including the whole kernel and all drivers, the development tools and all user programs; also, all of it is freely distributable.
• POSIX job control.
• Pseudoterminals (pty's).
• 387-emulation in the kernel so that programs don't need to do their own math emulation. Every computer unning Linux appears to have a math coprocessor. Of course, if your computer already contains an FPU, it will be used instead of the emulation.
• Support for many national or customized keyboards, and it is fairly easy to add new ones dynamically.
• Multiple virtual consoles: several independent login sessions through the console, you switch by pressing a hot-key combination.
• Supports several common filesystems, including minix, Xenix, and all the common system V filesystems, and has an advanced filesystem of its own, which offers filesystems of up to 4 TB, and names up to 255 characters long.
• Transparent access to MS-DOS partitions (or OS/2 FAT partitions) via a special filesystem: you don't needany special commands to use the MS-DOS partition, it looks just like a normal Unix filesystem. VFAT (WNT, Windows 95) support is available in Linux 2.0
• Special filesystem called UMSDOS which allows Linux to be installed on a DOS filesystem.
• Read-only HPFS-2 support for OS/2 2.1
• HFS (Macintosh) file system support is available separately as a module.
• CD-ROM filesystem which reads all standard formats of CD-ROMs.
• TCP/IP networking, including ftp, telnet, NFS, etc.
• Appletalk server
• Netware client and server
• Lan Manager (SMB) client and server
• Many networking protocols: the base protocols available in the latest development kernels include TCP,
• IPv4, IPv6, AX.25, X.25, IPX, DDP (Appletalk), NetBEUI, Netrom, and others.

Author : Nick Arahovas
For comments or suggestions mail at infonick@hol.gr
Last updated : 25-Feb-1997

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