2. CS 111.01Chapter 3 – Operating SystemsPage 49 Operating Systems An operating system is a set of programs through which a computer manages its resources. Its main functions are to: 1)Manage the computer hardware CPU performance & utilizationCPU performance & utilization Memory allocation & protectionMemory allocation & protection Input-output managementInput-output management Keyboard controlKeyboard control Mouse device driverMouse device driver Printer spoolingPrinter spooling Display monitorDisplay monitor 1)Manage the computer hardware CPU performance & utilizationCPU performance & utilization Memory allocation & protectionMemory allocation & protection Input-output managementInput-output management Keyboard controlKeyboard control Mouse device driverMouse device driver Printer spoolingPrinter spooling Display monitorDisplay monitor

3. CS 111.01Chapter 3 – Operating SystemsPage 50 2)Support applications software Word processors Electronic spreadsheets Computer graphics & games Database management

4. CS 111.01Chapter 3 – Operating SystemsPage 51 3)Establish a user interface Textual, with a command-line prompt Graphical, with windows, menus, and icons

5. CS 111.01Chapter 3 – Operating SystemsPage 52 Batch Processing Non-interactive execution of one or more programs with distinct input and output sessions Batch Processing Non-interactive execution of one or more programs with distinct input and output sessions Different Approaches To Processing Time-Sharing Multiple programs executing “simultaneously” (via time slices) on a single computer (either many users on a server or one user “multitasking”) Time-Sharing Multiple programs executing “simultaneously” (via time slices) on a single computer (either many users on a server or one user “multitasking”) Interactive Processing Execution of a program with additional input from the user and output to the user during execution Interactive Processing Execution of a program with additional input from the user and output to the user during execution Multiprocessing Multiple CPUs available within the computer system, either across a network or within a single machine (e.g., a supercomputer) Multiprocessing Multiple CPUs available within the computer system, either across a network or within a single machine (e.g., a supercomputer) RAM Process PCB CPU

6. CS 111.01Chapter 3 – Operating SystemsPage 53 Producer Consumer Waiting Full Queue Producer Consumer Waiting Empty Queue Resource Allocation Problems Mutual Exclusion If two processes require access to the same nonshareable resource at the same time, then both cannot be accommodated. Example: Producer & Consumer Mutual Exclusion If two processes require access to the same nonshareable resource at the same time, then both cannot be accommodated. Example: Producer & Consumer When extreme cases occur (either there are no resources available to be consumed, or no room for more to be produced), a “semaphore” is set to signal that someone must wait. Deadlock If two processes are simultaneously blocking each other’s progress, then neither one may be able to proceed. Deadlock One process copies from the floppy to the CD One process copies from the CD to the floppy

7. CS 111.01Chapter 3 – Operating SystemsPage 54 Computer Viruses A computer virus piggybacks on another file to “infect” a system. When a user runs an infected program, the computer starts by copying the program from the disk, where it is stored and inactive, into RAM, where it can be executed. The viral code begins running first, while the infected program is still quiescent. The virus copies itself in a part of RAM separate from the program so that it can continue its work even after the user starts running other software. Its initial work done, the virus passes control back to the infected program. When the user runs a different program, the dormant virus begins running again. It inserts a copy of itself into the previously uninfected software so that the cycle of virulence can repeat.

8. CS 111.01Chapter 3 – Operating SystemsPage 55 Fighting Viruses Various techniques have been developed to combat computer viruses. Generic Antiviral Program Flags activities--such as the alteration of critical sites in RAM or particular files on disk--that are likely to arise from a virus in action. Preventing these illicit acts will not eliminate the virus but can stop it from infecting additional programs or interfering with the computer's normal operation. Generic Antiviral Program Flags activities--such as the alteration of critical sites in RAM or particular files on disk--that are likely to arise from a virus in action. Preventing these illicit acts will not eliminate the virus but can stop it from infecting additional programs or interfering with the computer's normal operation. Signature Scanner Searches a user's disks looking for fragments of program code that appear in known viruses. Signature Scanner Searches a user's disks looking for fragments of program code that appear in known viruses. Antiviral Snapshots Capture mathematical "fingerprints" of crucial programs and data. Subsequent changes strongly suggest viral infection. Advanced algorithms can use the original fingerprints to recover a pristine program from the virus-altered version. Antiviral Snapshots Capture mathematical "fingerprints" of crucial programs and data. Subsequent changes strongly suggest viral infection. Advanced algorithms can use the original fingerprints to recover a pristine program from the virus-altered version.