Pilot: An Operating System for a Personal Computer

Q: How do the requirements of the Pilot operating system differ from the systems we have read about so far, and how does the design of Pilot reflect those differences?

Why?

• Single user
• Defensive protection
• Resources - not on fairness
• Network

Feature of Mesa language

• Object oriented (Pointer not exist)
• Single address space (No H/W protection)
• Strong type check

Hints

• Memory mapped file, pages used, can be moved
• OS trust the app hints
• No incentive for lying

Virtual memory

Virtual memory -> Space

Space.Create

• Space is servering as the unit of allocation.
• Space can be created as nest.

Space.Map

• Virtual memory is the only access path to the contents of files, and files are the only backing store for virtual memory.

Swapping

• The swapping between primary memory and backing store is performed in the units of spaces.
• The swapping stategy followed is to swap in the lowest (i.e., smallest) space containing the page.
• Space.Activate as a hint to be swapped in asap. Space.Deactivate is the inverse operation.

Advantage of all files memory mapped

• Decouple read / write and paging
• Reuse virtual memory functionality
• Stream I/O on top

Kernel / Manager

Kernel -> Mechanism

Manager -> Policy

Kernel: Memory page out, page in.

Manager: Decides which page to page out.