The UNIX Time-Sharing System

Review by Thorsten von Eicken, Jan 1998

"Goals"

• a system that's fun to use for program development and research
• powerful yet small
• build to be able to use

Achievements

Sophisticated operating system that runs on cheap machines

Simplicity (economy of features)

Full exploitation of small set of features

Important aspects

• File system namespace hierarchy, uniformity, and ubiquity
• mapping of devices into filename space (Multics)
  • same operations for devices as for files
  • same namespace
  • same protection mechanism
• Uninterpreted byte streams
• Non-privileged command shell, I/O redirection, pipes (Multics)
• Simple access control mechanism, set-uid, set-gid
• File system built around I-nodes
• File descriptors
• Portability

Questions

• mis-features in original UNIX?
• what happens if one deletes an open file?
• what do you think about their discussion of locking files?
• can you link across file systems?