Principles of Operating System and Software application

1. Principles of Operating System and Software application Prepared by Ms. Loren Chavez

2. Lesson Overview • What is an operating system? • Brief history of operating systems • Activity

3. The operating system is the software layer between the user applications and the hardware. • The OS is “all the code that you didn’t have to write” to implement your application.

5. Brief History of O.S. …..

6. In the beginning… • OSeswere runtime libraries The OS was just code you linked with your program and loaded into the computer. • First computer interface was switches and lights, then punched tape and cards.

7. Back in the transistor-based technology, early mainframes were first run by human operators. The unit of processing was a job, or predefined collection of commands that are executed without human interaction. Operators would handle one job at a time (e.g., submitting punch cards, running the program, and printing out results). Much computer time was wasted.

8. Later machines came with libraries of programs, which would be linked to a user's program to assist in operations such as input and output and generating computer code from human-readable symbolic code. • This was the genesis of the modern-day computer system. However, machines still ran a single job at a time.

9. Batch systems were next… • OS was permanently stored in primary memory • It loads a single job into memory(card reader, magnetic tape); • Executes job, creates output (line printer); • Loaded the next job, so on and so forth… • Card readers, line printers were slow, and CPU was idle while they were being used.

10. Batch system was introduced to collect a batch of jobs before processing them and printing out results. • A batch system consists of three stages— • job collection, • job processing, • and printing out results. All three stages can occur concurrently.

11. Since CPU processing and I/O processing can occur concurrently, a job that is waiting for its I/O to complete can be overlapped with a job that is using CPU. • This is now the beginning of multiprogramming, or allowing multiple programs to run concurrently.