Chapter Two -- Computer-System Structures -- Lecture Topics

• What is the typical configuration of the modern computing system? How do the controllers and memory manager fit in the model?
  
  
• What does it mean to say that a modern operating system is "interrupt driven?"
  
  
• How do interrupts work?
  
  
• What are system calls? How are they implemented?
  
  
• What roles do the OS and controllers play to implement I/O in a multiprogramming operating system? How does the OS communicate with an I/O controller? How does a controller communicate with the OS?
  
  
• How does an OS keep track of which processes are waiting for I/O to complete on which devices? How does the OS keep track of which processes are waiting their turn to use which I/O devices? What is the typical interaction of the OS with the device table during the servicing of an interrupt?
  
  
• How do synchronous and asynchronous I/O work?
  
  
• How does DMA differ from ordinary I/O?
  
  
• A DMA in progress typically causes the process currently executing in the CPU to be delayed. What is the nature of this delay? Why and how does it happen?
  
  
• Access (read or write) to primary memory takes a lot of time compared to CPU speed. Caching helps. Because of "locality" the system performs almost as well with a small amount of cache as it would with a much larger amount. That's fortunate because cache is expensive.
  
  
• Storage Hierarchies -- cost per bit versus speed, volatility, capacity.
  
  
• Memory Coherency problems -- between levels -- in parallel systems. Consider a multiprocessor with a data cache for each CPU when several caches contain a copy of the same word of primary memory. (This particular cache coherency problem is typically handled by hardware.) A similar problem arises when there are many copies of a file in existence in a distributed file system. This situation has to be handled by software.
  
  
• Hardware Protection mechanisms: The hardware and OS should prevent processes from harming the system and each other. The OS must be protected. We must be concerned about illegal I/O, illegal memory access, and "hogging" of the CPU. Tools: traps -- dual mode operation -- memory protection -- base and limit registers -- privileged instructions -- timers.
  
  
• Check your understanding. Is monitor mode the same as superuser status in Unix? No! Superuser is a user -- it does not run in monitor mode.
  
  
• Important to distinguish between the operating system and the hardware: What entity checks every address against the base and limit registers?
  
  
• Does the monitor *need* to access user memory?
  
  
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