Transcript sept20
CS 111 – Sept. 20 • Operating Systems – – – – definition origin responsibilities relationship with other software • Commitment: – Please read pp. 131-137 – Quiz on Wednesday. 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 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 Kinds of software • Application – fun & useful stuff for people – Hearts, Excel, Firefox, e-mail, 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 Responsibilities (1) • Security – 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 Responsibilities (2) • Files – 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)