CSC 315
Professor Stearns
Hardware needed to support concurrent programs

Once the decision is taken to run N programs at the same time, the hardware must support a number of new features.

1. A program is not allowed to do its own input/output
   Needed: kernel/user state, privileged instructions, instruction to request input/output, an operating system.

2. A program can't crash other programs
   Needed: A memory protection system and an exception system.

3. A fast method for switching control between programs is needed.
   Needed: exception system

4. I/O devices need a way to signal I/O completion
   Needed: interrupt system

5. Loaders need a way to allocate memory between programs
   Needed: A fast, foolproof allocation system that doesn't waste memory.