Chapter One -- Introduction -- Lecture Notes

• 1.0 Chapter Goals
  • Tour of OS Components
  • Describe Computer System Organization
  
  
• 1.1 What Operating Systems Do
  • Provide An Interface above the Level of the Bare Machine
  • Make the Computer More Efficient
  • Make Computer Use More Convenient
  • Controls and Coordinates Use of the Hardware - esp. I/O - prevents error and misuse.
  • Allocates Resources: CPU time, storage, devices ...
  • Provide Functions Commonly Needed by Application Programs
  
  
• 1.2 Computer-System Organization
  • The Typical System consists of one or more general-purpose CPU's and special purpose controllers sharing a common bus, including a memory controller.
  • A ROM-resident routine runs at boot time to perform initializations and load & execute the OS.
  • Hardware devices can interrupt the CPU - a signal sent along the system bus
  • A process can interrupt the CPU - by executing a special instruction - also by making an error.
  • An interrupt automatically causes suspension of the currently running process and transfer of execution to some predetermined section of code - typically a part of the operating system - an interrupt handler.
  • When an Interrupt Occurs, everything that will be needed to restart the currently running process must be saved. The interrupt automatically does some of the saving - for example the saving of the address of the current instruction. The interrupt handler code may perform other "context-saving" actions.
  • Typically methods for controlling peripheral devices are quite diverse and complex. Operating systems have "device driver" code - drivers corresponding to each type of device controller. The job of the device driver is to receive simple high level commands from the OS, translate the commands, and communicate with the device to achieve the desired effects.
  • Typically drivers have to load bit patterns into registers within the devices in order to "command" the device to perform an action.
  • Typically, when a device finishes performing a data transfer it notifies the OS by sending an interrupt.
  • With Direct Memory Access (DMA) a controller can transfer an entire block of data between device and primary memory, and interrupt the CPU only once, after the entire block has been transferred.
  
  
• 1.3 Computer-System Architecture
  • OS's must rise to the challenge of operating various kinds of multiprocessor systems efficiently: SMP's, multiple cores, blade servers & clustered systems.
  
  
• 1.4 Operating-System Structure
  • 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, protection, and security.
  • 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.
  
  
• 1.5 Operating-System Operations
  • 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.
  • In your mental model of how an OS works, do you see the OS as a part of the system that is always executing and always monitoring user processes? Typically "the OS" is NOT running all the time. In fact this would make it impossible for user processes ever to execute on a uniprocessor. An OS can employ hardware protection mechanisms to ensure that it will not lose control of the system, even during periods when the OS is suspended.
  
  
• 1.6 Process Management
  • A process is a program in execution. An OS has to create, delete, suspend, resume, and synchronize processes.
  • An OS must provide a mechanisms by which processes can communicate.
  
  
• 1.7 Memory Management
  • The OS has to allocate memory to processes and deallocate memory that is no longer in use. It has to keep track of which portions of memory belong to which processes
  • Sometimes an OS has to take memory away from a process temporarily.
  
  
• 1.8 Storage Management
  • OS's are responsible for implementing file systems on secondary storage: e.g. creating and deleting files & directories, and allocating/deallocating storage space on disk.
  
  
• 1.9 Protection and Security
  • Although the difference between computer protection and security has become blurred, our text makes an effort to preserve a clear distinction between the two.
  • An OS must perform "gatekeeper" functions - making sure that users provide proper credentials before being given access to system resources. This is "protection". The doorman at an expensive hotel and the sentry at a military facility are doing protection work.
  • gatekeepers, door men and sentries certainly cannot adequately work to prevent damage or failure that happens inside the facility that they guard. Besides protection, an OS must also be concerned with "security" - insuring that processes always use resources properly. When casino owners watch people gambling, it's security work. The bouncer in a bar is there for the security of the establishment.
  
  
• 1.10 Distributed Systems
  • A distributed system is basically a bunch of computers connected to each other via a network.
  • A distributed operating system is an operating system that makes a distributed system operate as if it were a single computer.
  • A major challenge of the current generation is to build reliable and efficient distributed operating systems.
  
  
• 1.11 Special Purpose Systems
  
  
• 1.12 Computing Environments