Operating Systems (OS)

- Software platform on which other programs run
- Provides a connection between application programs and the computer hardware
- Major tasks
   - Starting the computer (booting or boot strap)
   - Managing files
   - Program and memory management
   - Ensuring security
   - Providing a user interface

Managing Files:
- OS keeps track where all files are located
- Creates and manages directory structure
   - Free space
   - Used space
   - Formerly used space (see defragmentation)

Program and memory management:
- OS is responsible for
   - Sending a program to the CPU
   - Allocating primary storage for the program
   - Controlling other devices the program requires
- Multiprogramming and Multitasking
   - More than one program in memory at once
   - OS keeps track of memory for each program
   - One program runs until it needs data from the user, then the OS    - switches to the other program
- Time sharing
- Virtual memory

Ensuring security:
- Access control – Who has access to the computer; needed when network connected
- File permissions – Read and/or modify security permissions for individual files
- Logging – Audit trail of who has accessed the computer and what actions they performed

Providing a User Interface:
- Text or command line interfaces
- Graphical User Interfaces (GUIs)
- Voice interface