Introduction to Operating System – Download PDF Notes

Operating System-History

Every computer system must have at least one operating system to run other programs. Applications like Browsers, MS Office, Notepad Games, etc., need some environment to run and perform their tasks. The OS will assist the user to communicate with the computer without knowing how to speak the computer’s language. It is not possible for the user to use any computer or mobile device without having an operating system. Some refer to an operating system as system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems arranges tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory. The operating system acts as an intermediary between programs and the computer hardware, even though the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it.

• Initially, in the 1940s, the electronic digital systems had no operating systems.
• Electronic systems at that  time were programmed on rows of mechanical switches or by jumper wires on plugboards.
• They were special-purpose systems that, for example, generated ballistics tables for the military or controlled the printing of payroll checks from data on punched paper cards.
• After programmable general-purpose computers were discovered , machine languages(consisting of strings of the binary digits 0 and 1 on punched paper tape) were introduced that sped up the programming process (Stern, 1981).
• The OS/360 was used on most IBM mainframe computers beginning in 1966, including computers used by the Apollo program.
• In the early 1950s, a computer could function only one program at a time.
• Each user had one use of the computer for a limited period and would arrive at a scheduled time with their program and data on punched paper cards or punched tape.
• The program would be loaded into the machine, and the machine would be ready to work until the program completed or crashed.
• Programs could generally be debugged via a front panel using toggle switches and panel lights.
• It is said that Alan Turing was a master of this on the early Manchester Mark 1 machine, and he was already deriving the primitive conception of an operating system from the principles of the universal Turing machine.

Operating System-Notes

The OS will assist the user to communicate with the computer without knowing how to speak the computer’s language. It is not possible for the user to use any computer or mobile device without having an operating system. Some refer to an operating system as system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems arranges tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory.

Types of Operating System

• Batch Operating System
  • A set of similar jobs are stored in the main memory for execution.
  • A job gets assigned to the CPU, only when the execution of the previous job completes.
• Multiprogramming Operating System
  • The main memory consists of jobs waiting for CPU time.
  • The OS selects one of the processes and assigns it to the CPU.
  • Whenever the executing process needs to wait for any other operation (like I/O), the OS selects another process from the job queue and assigns it to the CPU.
  • This way, the CPU is never kept idle and the user gets the flavor of getting multiple tasks done at once.
• Multitasking Operating System-
  • Multitasking OS combines the benefits of Multiprogramming OS and CPU scheduling to perform quick switches between jobs.
  • The switch is so quick that the user can interact with each program as it runs
• Time Sharing Operating System-
  • Time-sharing systems require interaction with the user to instruct the OS to perform various tasks.
  • The OS responds with an output.
  • The instructions are usually given through an input device like the keyboard.
• Real Time Operating System-
  • Real-Time OS are usually built for dedicated systems to accomplish a specific set of tasks within deadlines.

A thread is a lightweight process and forms the basic unit of CPU utilization. A process can perform more than one task at the same time by including multiple threads.

• A thread has its own program counter, register set, and stack
• A thread shares resources with other threads of the same process the code section, the data section, files and signals.
• A new thread, or a child process of a given process, can be introduced by using the fork() system call.
• A process with n fork() system calls generates 2ⁿ – 1 child processes.
• There are two types of threads:
  • User threads
  • Kernel threads
  • Java thread, POSIX threads.
  • Example : Window Solaris.

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