What does history tell us?

Take a stroll down memory lane :

 
		1985 		Present 		factor

MIPS		1		300		300

/MIPS		100 K		50		2000

Memory		128 KB		64 MB		500

Disk		10 MB		2 GB		200

Tape		200 MB		1 TB		5000

How to deal with this as a designer ?

Tradeoffs ? Time varing techniques

Methods which vary as the problems change ...

B<>History Phase 1 :

Cheap Humans - Expensive Machines

• Single user (highly protected environments)
• Batch programs (Job Control Languages)
  (load, run, print, perform operation X etc)
• Data Channels / interrups (overlap I/O and computation). DMA : direct memory access.
• Memory Proection and relocation
  Multiprogramming : several programs run at the same time ; users share system.
  Multiprogramming requires memory protection to keep bugs in one program from crasging system or corrupting other program)

What does this mean ?
Operating System become large complex programs that must manage all these interactions.
Each step of operation seems logical, but at some point ...

B<>History Phase 2 :

Cheap Machines - Expensive Humans

• Interactive Timesharing : cheap terminals with multiple users interacting simultaneously.
  CPU time shared between all users. But what about Thrashing (less time in CPU more for I/O).
• Personal computing - everyone has their own computer.
• Resource sharing now with a Network.

BUT - what does this all mean ?

• Multics announced in 1963 RAN in 1969
  (Unix based on Multics but simpler!).
• NT under development for the last 7 years - STILL DOESN'T WORK.
• Situation today much like the past :
  Operating Systems are enormous complex things
  small OS : 100 K lines of code, to big OS : 10 M lines of code.

So where do we go from here ?

Key Aspect of this course :

"Understand Operating Systems so we can simplify them"