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

2. 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

3. 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

4. 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

5. 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

6. 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