Chapter One (A) -- Introduction -- Lecture Topics

• For some operating systems EFFICIENCY (mainframes and mini's) is the primary goal.
  
  
• In other cases the primary goal is CONVENIENCE to the user (Personal Computers).
  
  
• STABILITY is a goal to think about too.
  
  
• In still other cases a delicate balance between CONVENIENCE and EFFICIENCY is pretty important (workstations).
  
  
• OS as GOVERNMENT
  
  
• OS as RESOURCE ALLOCATOR -- this relates to the model of an OS as queueing system.
  
  
• OS as CONTROL PROGRAM
  
  
• It is not feasible to use computer hardware directly. Software is required to act as an intermediary between user and hardware. The OS can be viewed as a collection of services that are needed in common by all or most programs.
  
  
• It's important to realize that by learning about the history of operating systems, you get better at understanding current operating systems and the future of operatings systems. In other words, it's (probably) relevant to you the student to know about the history of operating systems.
  
  
• Important themes in OS development:
  
  
  • Interrelationship of hardware development with OS development
    
    
  • The manner in which the quest for greater CPU utilization drove the development of operating systems.
    
    
  
  
  
• Earliest operating systems were simple job-sequencers. Batching reduced set-up time. Disk drives allowed for a job pool and more scheduling choices.
  
  
• Multiprogramming was development pushed into existence by the need for greater CPU utilization. A "QUANTUM LEAP" in sophistication of the OS was required -- e.g. context switching, memory management, scheduling, concurrency management.
  
  
• Time-sharing was a "natural" follow-on to multiprogramming that allowed a return to "interactive" computing.
  
  
• Time-sharing tends to make greater demands for swapping and virtual memory.
  
  
• Traditional time-sharing requires implementing a file system -- not the same as just the ability to write and read disk sectors.
  
  
• At first security and protection was a low priority for personal computers. Now that networked and multitasking personal computers are common, security and protection has become a high priority.
  
  
• Discuss how worms and viruses are rendered less powerful in environments where there is good file protection and secure separation of user privileges.
  
  
• Multiprocessor systems have hardware that offers certain advantages -- increased throughput; economy of scale through sharing of memory, peripherals, and power supplies; increased reliability; fault tolerance; and graceful degradation. However it is quite a challenge to design an operating system for a multiprocessor, especially a (desirable) completely symmetric system. "Virtually all modern operating systems ... now provide support for SMP."
  
  
• Many computers are now intended to remain connected to a network and function either primarily as servers or clients. Operating system designs have been adapted to optimize the performance of such computers -- network operating systems and distributed operating systems. This is an active area of operating system research today.
  
  
• Clustered systems are a form of redundancy that provides fault tolerance. Cluster technology is an area of active development.
  
  
• Operating systems for real-time applications have special requirements. "A real-time system has well-defined, fixed time constraints. Processing must be done within the defined constraints, or the system will fail." Keep in mind that "real-time" is not just about being able to do things quickly. Consider the requirements of a computing system that plays a video -- each frame is supposed to appear and disappear at a certain "objective" time -- a time as measured "out there" in the world of the audience. The system fails if it changes a frames too late or too soon.
  
  
• It is interesting to notice when the same OS problem "pops up" in different eras. Currently programmers for handheld computers are struggling to work with a very limited physical memory of perhaps as little as 512KB. This same problem was faced by programmers of the early mainframes, the early PC's, and embedded systems.
  
  
• Feature migration -- "... the features developed for a large mainframe system have moved to microcomputers over time.