OS学习笔记：Lecture 3

OS architecture

 

What isOS?

1. Not solvable.
2. Goals:
   1. User goals: easy to learn, reliable, safe and fast.
   2. System goals: easy to design, implement and maintain, flexible.
3. Principle:
   1. Policy: OS undertake
   2. Mechanism: application undertake
   3. Policy mechanism devided.

 

Simplestructure

1. Dos
2. Unix
3. Microkernel
   1. Kernel: LPC (hub, connect server); HAL
   2. Example: Mach
      1. IPC: between threads via ports -> 函数调用 bottleneck
         1. Synchronous IPC
            1. Send, wait
            2. Send copy to kernel; kernel copy to wait
         2. Rendezvous model
            1. Kernel copy send's message to wait
            2. Must multi threads
         3. Multi threads -> 轮询 select
      2. Memory object management -> virtual memory
      3. Device support using IPC
      4. User multipocessing: user threads map to same kernel thread
      5. Multicomputer support -> 集群 task 调度
      6. Mach 2.5 -> NeXT, Encore, OSF
   3. Not take over the world
      1. Hardware standardization
      2. Software standardization
4. Exokernel structure
   1. OS devided from critical path: kernel never provide any service
   2. Example
      1. Program visit hardware directly
      2. Library OS can be customized for applications ->LKL
   3. Customer-support issues