What do OS’ do?

• Process execution, scheduling
• Inter-process communication
• Hardware I/O
• Hardware abstraction
• Filesystems
• Access control (system, files, memory, devices)
• Accounting

Operating systems mediate software access to resources, whether concrete (disk space, I/O devices) or abstract (time, security)

“Real-Time” Operating Systems?

• Predictable behaviour
• Notable deadlines that need to be met, with clear priorities of various tasks
• Tasks are periodic

Hard real-time (“or else”):

• Has hard deadlines (emphasis on dead)
• Example: cars, planes, mars robots, etc.

Soft real-time (“mostly”):

• Has soft deadlines
  • i.e., deadlines are important (mostly)
  • but slippage is acceptable
  • Example: Frame drops in HQ video stream
• Example: A/V, transactions, simulation

Non-real-time

• Everything else!

Important concepts

• Interrupts
• Memory and I/O interfacing
• Multiprocessing
• Privilege modes
• Virtual memory
  • Virtual and physical addresses
  • Page tables and TLBs