Necessary Background for OS Dr. John Abraham Professor UTRGV Dr. John Abraham, Professor UTRGV

Dr. John Abraham, Professor UTRGV Software Application software For specific task that a user runs System software Operating System and other programs that are not application software. Allows application programs to run Allows application programs to use I/O devices through syscalls Dr. John Abraham, Professor UTRGV

Dr. John Abraham, Professor UTRGV Operating system Sits between user and the hardware so that user need not know the details of the hardware Users can’t access computer resources directly, OS handles it for the user Explain experiences with pokes and peeks If a user is allowed to use resources directly such as a printer, the user can tie up the resource from others. Explain my experiences with plotters Dr. John Abraham, Professor UTRGV

Functions of Operating System Resource management: CPU (processor management) using PCB, Scheduler, Dispatcher Memory management (cache, RAM) I/O devices management Storage management, Directories, subdirectories, file Allocation Tables, etc. Security – who can access what Controls (governs) execution of all programs Goals of OS Ease of use (convenience), GUI, command line interface (CLI) of character line interface Efficiency Dr. John Abraham, Professor UTRGV

Types of Operating Systems System Operator (SysOps) Batch processing. Explain my experiences Job – program, input data plus control instructions User does not interact with the operating system Multiprogramming, many processes One processor at a time is allocated to CPU. The program may exit when waiting for IO, and another process can use the CPU. Large programs may monopolize the CPU, when small programs simply wait Multi-tasking Time slice or priority will switch processes in/out of cpu (round robin, etc), interrupts (Hardware, software) based context switching (PCB) Multi-processing. Many processors. One process to each processor, or portions of each process handled by several cpu’s Real-time. Time dependent for mission critical. Immediate response needed. Military, gas refinery, etc. Dr. John Abraham, Professor UTRGV

Generations of operating system 1940s Users had complete access to machine language, so no OS. 1950s Jobs oriented OS. Significant time was lost between jobs. Batch oriented. Sysop decided what is stored on which tape. 1960s supported Multiprogramming. Several processes brought into RAM. A job monopolized the CPU until I/O is needed. Then swapped out. OS decided what is stored on which tape, issued instruction to sysop to load the tape. Timesharing systems appeared here. 1970s IBM 360 – multimode system that supported all the above. Late 1970s (unbundled hardware from software) and networking and distributed data processing. Dr. John Abraham, Professor UTRGV