You could go back 4000 years when the Greeks and the Chinese used the abacus. It's argued that Charles Babbage's Analytical Engine was the first computer back in the 1833. It had 1000 words of memory, 50 decimal digits each. Capable of input, processing, memory, output. Ada Lovelace became famous for programming it. I suppose the operating system was part mechanical and part human.
Then you had the vacuum tube machines that were programmed by patching wires. Later punch card and paper tape fed machines, then magnetic tape and so on. OSs go back a long ways. IBM started building machines back in the late 1800's. UNIX is probably one of the oldest operating systems still in wide use today that still has somewhat of a resemblence to it's origins at the very base level. Even UNIX is a young operating system at ~35 years.
Linux (UNIX like kernel) was started in 1991 by Linus Torvolds as you know. Although most people think of the entire operating system which is based on GNU software (UNIX like) which has been in development for quite some time prior to the Linux kernel (I believe since the early 80s).
I'm not real familiar with BeOS other than I did download and install it at one point and I found it also to be very UNIX like underneath, in fact I wonder if a lot of it didn't come from BSD, maybe someone can enlighten me on this one. And I don't believe the BeOS OS started development until the mid to late 1990's, someone correct me.
Also CPM was created in 1954. And IBM had operating systems long before that. I used MVS on their mainframes which I believe to be at least as old as UNIX, could be wrong. Don't know for sure what they used on their big mainframe systems prior to MVS. But any of the OSes running today have been significantly enhanced over their predecessors because of advances in hardware making much more possible.
Here's an interesting link I just found:
http://www.geocities.com/alienhardware/index10.htm[ January 24, 2003: Message edited by: void main ]