For the computer geek, the world began at midnight on January 1, 1970, the day we now know as the epoch. This is the day that Unix was created (actually, Unix was created in 1969, but it's clock started in 1970). Unix was created by Brian Kernigan and others at AT&T Bell Laboratories. From this moment all Unix machines date themselves - the date is stored internally as the number of milliseconds from the epoch. As of the writing of this chapter of this book, 1033530810062731 milliseconds have transpired since that important moment.
And computer geeks around the world gazed upon Unix and saw that it was Good.
Years passed since January 1, 1970, and during that time other operating systems were written. Some stood the test of time, others didn't. Some that stood the test of time perhaps should not have, but did anyway. And many flavors of Unix were developed by many different companies (for instance: Solaris developed by Sun Microsystems, HP-UX developed by Hewlett Packard, on so on). These flavors of Unix were almost always closed and proprietary implementations.
Also during the time from the epoch until now, a certain operating system (Windows) gained wide use around the world, and runs on the Intel x86 processor. Since Windows is popular, and runs on Intel chips, there are a lot of computers based on the Intel architecture.
But here is the problem: most computers based on the Intel architecture run the Windows operating system. Back in 1991, a college student from Finland was dissatisfied with the inferior operating system running on his Intel hardware, so he posted the following message to the comp.os.minix newsgroup (Minix is a small implementation of Unix):
Hello everybody out there using minix - I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones.
The student was Linus Torvalds, and his hobby has become the Linux operating system.
Linux is a powerful, stable, securable, free, open source, POSIX-compliant operating system developed by Linus Torvalds with the help of thousands of programmers around the world. It started on the Intel 386/486 platform, but has since been ported to many other architectures: Macintosh, Alpha, SGI, VMS, even the Palm Pilot.
Linux specifically refers to the kernel software, the code that is the guts of the operating system. The other system software, such as the tools grep, ps, etc., is taken from multiple sources, primarily the GNU Project (GNU stands for Gnu's Not Unix). Thus, Linux is more properly referred to as "GNU/Linux." See http://www.gnu.org for their take on it.
Oh, by the way. Did we mention Linux is free?