1. CS 111 – Sept. 20 Operating Systems Commitment: definition origin
responsibilities
relationship with other software
Commitment:
Please read pp
Quiz on Wednesday.

2. Original purpose Streamline process of doing jobs on the computer.
Reduce overhead spent between jobs.
Batch processing:
Plan day’s jobs in advance
Give jobs to a computer operator
Job Control Language: enter commands to the OS
Computer operator not practical
Confidentiality
Some applications like a game are inherently interactive; require fast turnaround

3. Utilization Historically… CPU time used to be very expensive
2 ways to run jobs
Interactively
In batch mode. This is useful if jobs must complete by some deadline in a real-time system.
Time sharing
Many users, but just 1 expensive machine.
Do not let any one job monopolize machine.
Have several jobs running at same time; give each a turn at the CPU: multi-programming
Today: 1 user has many jobs per day – use same technique

4. Kinds of software Application – fun & useful stuff for people
Hearts, Excel, Firefox, , PPT, …
System utilities – programs that make the computer more useful, added features
Formatting a disk, compress data, play DVD
OS shell – accept commands from user; display error message
OS kernel – major responsibilities; manage resources
Note: distinctions can be blurred – the distinctions among the categories are not exact

5. Responsibilities (1) Security CPU Memory
Require many password combinations
Penalties for mistake
Super user & diagnostic tools to detect abnormal activity
CPU
Be aware of all currently running programs
Synchronization: make sure 2 executing programs don’t interfere with each other
Scheduling: deciding which program to execute now
Memory
Decide which files (or portions of files) should be in RAM
Virtual memory: shuffle pages in and out of RAM to give illusion that RAM is bigger than it really is

6. Responsibilities (2) Files I/O and network
Maintain folders
Keep information about each file: name, size, owner, type, permissions
User quotas
I/O and network
Device drivers
User interface (shell or GUI)