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Operating Systems I

Explore the evolution of operating systems from batch jobs to time-sharing, understanding how OS manages resources, processes, and interfaces for efficient computer operations. Learn about the OS shell, kernel components, file management, device drivers, memory management, scheduler, and dispatcher. Discover the types of software, utilities, and the coordination between applications and utilities within an OS environment.

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Operating Systems I

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  1. Operating Systems I An Introduction to Operating System Concepts

  2. OS Introduction • Computer applications today require a single machine to perform many operations and the applications may compete for the resources of the machine. • This demands a high degree of coordination • This coordination is handled by system software known as the operating system

  3. Evolution of Operating System • OS for batch jobs • Program execution required significant preparation of equipment • Program execution (job) • OS was a system to simplify program setup and simplify transition between jobs • Physical separation of users and equipment led to computer operators

  4. OS Evolution (cont’d) • Users left jobs with the operator and came back the next day (batch jobs) • Users had no interaction with computer during program execution. Maybe okay for some applications, but not for all.

  5. OS Evolution • OS for Interactive Processing • Allowed programs to carry on dialogue with user via remote terminals (workstations) • Real-time processing • Users demand timely response • Machines too expensive to serve only one user • Common for several users to want interactive services at the same time

  6. OS Evolution (cont’d) • OS for time-sharing • To accommodate multiple real-time users, the OS rotates its various jobs in and out of execution via time-sharing • Each job gets a predetermined “time slice” • At end of time slice current job is set aside and a new one starts • By rapidly shuffling jobs, illusion of several jobs executing simultaneously is created

  7. OS Evolution (cont’d) • Without time slicing, a computer spends most of its time waiting for peripheral devices or users • A collection of tasks can be completed in less time with time-sharing than when completed sequentially

  8. Different Operating Systems on the Same Machine ? • It is possible to have more than one operating system available to be used on a machine. • Only one operating system is run at a time, though. • Examples: • VAX -- VMS or Ultrix • PCs -- DOS, Windows, or Linux

  9. Types of software • Applications software • Performs tasks specific to the machine’s utilization. • System Software • Performs tasks common to computer systems in general • Operating systems vary based on the hardware they’re used on

  10. Types of software (cont’d) • Utility software • Provides fundamental activities, yet not included with OS • “Extends” the OS • Distinction between applications and utilities is often vague • Distinction between OS and utilities is also vague

  11. The OS Shell • Defines interface between OS and users • Windows GUI • UNIX command line • UNIX users can choose among a variety of shells • csh is the “C shell” • tcsh is an enhanced “C shell”

  12. OS Shell interface Users Users Users O / S shell

  13. The OS Kernel • The internal part of the OS is often called the kernel • Kernel Components • File Manager • Device Drivers • Memory Manager • Scheduler • Dispatcher

  14. OS File Manager • Maintains information about the files that are available on the system • Where files are located in mass storage, their size and type and their protections, what part of mass storage is available • Files usually allowed to be grouped in directories or folders. Allows hierarchical organization.

  15. OS Device Drivers • Software to communicate with peripheral devices or controllers • Each driver is unique • Translates general requests into specific steps for that device

  16. OS Memory Manager • Responsible for coordinating the use of the machine’s main memory • Decides what area of memory is to be allocated for a program and its data • Allocates and deallocates memory for different programs and always knows what areas are free

  17. OS Scheduler • Maintains a record of processes that are present, adds new processes, removes completed processes • memory area(s) assigned • priority • state of readiness to execute (ready/wait)

  18. OS Dispatcher • Ensures that processes that are ready to run are actually executed • Time is divided into small (50 ms) segments called a time slice • When the time slice is over, the dispatcher allows scheduler to update process state for each process, then selects the next process to run

  19. OS Summary • Shell -- interface to user • File Manager -- manages mass memory • Device Drivers -- communicate with peripherals • Memory Manager -- manages main memory • Scheduler & Dispatcher -- manage processes

  20. Utilities • Operating systems usually come with some associated utility programs • UNIX usually has the text editors emacs and vi (and sometimes pico) • UNIX has its own sort utility • UNIX has its own mail utility

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