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Ch1 OS 及 System types介紹 (System types(computing environment) (B. Time…

- - - - (1) Increased throughput
        Note: The speed-up ratio with N processors is not N, however; it is less than N. Because of resource Contention & Communication between processors.
      - (2) Increased Reliability
        (i) Graceful degradation
        (ii) Fault Tolerant system ( able to continue working to a level of satisfaction in
        the presence of errors or breakdowns.)
      - (3) Economy of Scale
        Can cost down because of sharing resources like memory and bus.etc
    - - (1) ASMP
        
        Advantage: Easy to develop OS ( can be modified from single CPU )
        
        Disadvantages ( In contrast to SMP ): low efficiently ( Master CPU will be the bottleneck ) / low reliability ( if Master CPU breaks down, must choose a new one to replace it )
        
        Def: Every processor is responsible of different jobs ( Master-slave )
      - (2) SMP (圖)
        
        Def: Each peer CPU processor performs all tasks, including operating-system functions and user processes. ( identical working ability )
        
        Note: Each CPU processor has its own set of registers, as well as a private—or local— cache. However, all processors share physical memory over the system bus.
        
        Advantage: The opposite of ASMP ( can run simultaneously —N processes can run if there are N CPUs—without causing performance to deteriorate significantly.)
        
        Disadvantage: The development of the OS of SMP is much more complicated than ASMP ( need the mechanism of exclusive access )
    - - Def: multiple computing cores reside on a single chip.
      - Advantage: (1) more efficient than multiple chips with single cores ( because on-chip communication is faster than between-chip communication.) (2) uses significantly less power than multiple single-core chips, an important issue for mobile devices as well as laptops.
      - a multicore processor with N cores appears to the operating system as N standard CPUs.
  - - - 1. Def: Processing must be done within the defined constraints, or the system will fail. ( This system must ensure the critical tasks complete on time)
      - eg. weapon systems / industrial control systems / Nuclear Safety control / robots control
      - System design must consider:
        
        (1) Any factor that may affect Time ( Algorithm / signal & data transfer / system processing latency)
        
        (2) Any device and mechanism that may cause processing time too long should not be adopted ( e.g: Disk / Virtual memory )
        
        (3) Reduce the intervention of kernel ( mostly, hard real time system do not have OS )
        
        (4) General OS(eg.UNIX/ Linux/ Windows/ Solaris) doesn't support hard real time features
        
        (5) Cannot coexist with Time-sharing system ( because of Virtual memory )
    - - Def: This system must ensure the real-time process has the highest priority than the others and retain this level of priority until it completed
      - System design must consider:
        
        (1) CPU scheduling: preemptive ( don't support "Aging")
        
        (2) Reduce kernel Dispatch latency
        
        (3) Current OS support soft real-time features
        
        (4) Can be coexisted with Time-sharing system ( support virtual memory, but it requires the Page of real-time must be in the memory until work done )
      - eg. Multimedia system / Virtual Reality / Science Simulation.etc
  - - - (1) Slower process (i) High energy consumption of power (ii) cooling problem
      - (2) Small memory size
      - (3) Small display screen
      - Software design: The operation should not be overly complicated
      - The program should be simplify
      - The content of the display should be reduced (e.g mobile page)