1. Paper Discussions
Karthik Dantu
Steve Ko

2. Unix Time-Sharing System
History
CTSS ( )
Multics ( ) – MIT, GE, Bell Labs
Seamless store for data access (everything is a segment)
Dynamic linking
Hotswap, multi-processor support
Hierarchical file system, shell, security
Third version - Uniplexed Information and Computing Service (Unics  UNIX)
PDP-7 and PDP-9s ( )
PDP-11/20
Demonstrate OS capability on hardware costing as little as $40,000

3. Features Tools Assembler editor linking loader symbolic debugger
Languages: C compiler, BASIC interpreter, Fortran, Snobol
YACC
macro processor
Fully self-supporting

4. Filesystem Most important job of UNIX
Regular files, directories, special files
Removable file systems
Set-user-id bit – precursor to ‘sudo’?
No distinction between random/sequential access
Simple set of calls – open, close, create, seek
Locks – neither necessary or sufficient

5. Processes Layout – very similar to modern processes Fork
Process hierarchy
Pipes – first attempt at IPC
Semantics unclear – blocking/non-blocking?
Process synchronization
Shell
Filtering/unix-pipes
Internal/external commands?

6. Perspective Usage – primary objective
Make it interactive as opposed to batch-processing
Minimalism due to size constraints
Maintaining itself
First Open Source system?

7. Hints For Computer Design
Algorithm vs Design
Fundamentally a tradeoff
Much more internal structure – potentially flexible
Success less well-defined
Guiding questions
Why? Improve functionality, speed, fault-tolerance
Where? Ensuring completeness, designing interfaces, better implementation

8. Keep it Simple Do one thing; do it well Don’t generalize
Get it right (!)
Corollaries
Make it fast, not general
Don’t hide power
Use procedure arguments/parameterize
Leave it to the client
When in doubt, leave it out
Exterminate features

9. Continuity
Keep the basic interfaces stable
Keep a place to stand

10. Implementation Plan to throw one away Keep secrets Divide and Conquer
Use a good idea again
Completeness
Make the normal case fast
The worst case must make some progress

11. Speed Split resources Use static analysis Dynamic translation
Use hints
When in doubt, use brute force
Compute in background
Safety first
Shed load

12. Fault Tolerance End-end Log updates
Make actions atomic and re-startable