On Saturday 28 August 2004 05:14 pm, Greg Meyer wrote:

> But then how was the first UNIX system created?

On a PDP-11, likely using RSTS or RSX-11.

It's really a 'bootstrapping' process (called so because you're lifting 
yourself by your bootstraps).  From bare iron you write a loader that loads 
from something simple - old times it was paper tape.  On the first paper tape 
you have a very simple control program, all it might do is execute other 
programs and manage devices a bit.  Using that you write the machine language 
code to write an assembler, then use the assembler to write better programs 
(maybe a disk driver and a file system), then use the improved tools to write 
a better control program, then an operating system, etc.  

With outside hardware you can write a lot of the system on another computer 
and have the advantage of terminals, editors, compilers, linkers - file 
systems!  Build things and put then to a floppy or hard disk, them boot it on 
the new system.  Once in place start putting the tools and such together - 
for Linux it was nice because there was a whole bunch of GNU stuff that could 
run.

The old term of bootstrapping lives - you 'boot' your system up when it powers 
up.  First the BIOS runs, then it loads a better loader from the hard drive, 
then the loader load the operating system.  (In the old days I had to use the 
front panel switches to load a simple paper tape loader, then load a loader 
from paper tape and then tell it to load things from the hard drive.  Yup, 
men were *men* and computers were made of *iron* in those days.)

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