space travel
nick...@googlemail.com
The following text was written by Dennis Ritchie about the early
development of Unix at Bell Labs
Also during 1969, Thompson developed the game of `Space Travel.' First
written on Multics, then transliterated into Fortran for GECOS (the
operating system for the GE, later Honeywell, 635), it was nothing
less than a simulation of the movement of the major bodies of the
Solar System, with the player guiding a ship here and there, observing
the scenery, and attempting to land on the various planets and moons.
The GECOS version was unsatisfactory in two important respects: first,
the display of the state of the game was jerky and hard to control
because one had to type commands at it, and second, a game cost about
$75 for CPU time on the big computer. It did not take long, therefore,
for Thompson to find a little-used PDP-7 computer with an excellent
display processor; the whole system was used as a Graphic-II terminal.
He and I rewrote Space Travel to run on this machine. The undertaking
was more ambitious than it might seem; because we disdained all
existing software, we had to write a floating-point arithmetic
package, the pointwise specification of the graphic characters for the
display, and a debugging subsystem that continuously displayed the
contents of typed-in locations in a corner of the screen. All this was
written in assembly language for a cross-assembler that ran under
GECOS and produced paper tapes to be carried to the PDP-7.
Space Travel, though it made a very attractive game, served mainly as
an introduction to the clumsy technology of preparing programs for the
PDP-7. Soon Thompson began implementing the paper file system (perhaps
`chalk file system' would be more accurate) that had been designed
earlier. A file system without a way to exercise it is a sterile
proposition, so he proceeded to flesh it out with the other
requirements for a working operating system, in particular the notion
of processes. Then came a small set of user-level utilities: the means
to copy, print, delete, and edit files, and of course a simple command
interpreter (shell). Up to this time all the programs were written
using GECOS and files were transferred to the PDP-7 on paper tape; but
once an assembler was completed the system was able to support itself.
Although it was not until well into 1970 that Brian Kernighan
suggested the name `Unix,' in a somewhat treacherous pun on `Multics,'
the operating system we know today was born.