Operating Systems

Operating Systems

Computer Services What things can your computer do? • Calculator • Word processing • Web browsing • Photoshop • Paint program • Games These are all pieces of Software!

Software Software applications usually have very nice interfaces – • Buttons • Icons • Menus • Instructions • Graphics

Computer Components How does the computer perform these functions? • Memory • Disk drive • Circuit Board • Keyboard • Monitor These are pieces of Hardware!

Hardware Hardware components usually have pretty difficult interfaces. Machine Language Program for MIPS Machine [0x00400000] 0x8fa40000 lw $4, 0($29) ; lw $a0, 0($sp) [0x00400004] 0x27a50004 addiu $5, $29, 4 ; addiu $a1, $sp, 4 # argv [0x00400008] 0x24a60004 addiu $6, $5, 4 ; addiu $a2, $a1, 4 # envp [0x0040000c] 0x00041080 sll $2, $4, 2 ; sll $v0, $a0, 2 [0x00400010] 0x00c23021 addu $6, $6, $2 ; addu $a2, $a2, $v0 [0x00400014] 0x0c000000 jal 0x00400020 [main] ; jal main [0x00400018] 0x3402000a ori $2, $0, 10 ; li $v0 10 [0x0040001c] 0x0000000c syscall

Operating System User Operating System Hardware

Virtual Environments Operating Systems make the computer applications organized • Hallway • Desk • File Cabinet • Book Shelf

Virtual Environments You’ve seen Operating Systems already: • Windows whatever • UNIX • Mac Usually work with WIMPs (Windows, Icons, Menus, Pointers)

Booting up • If the OS is the program that runs the other programs, how does the OS program get loaded and run in the first place? • When you turn on the computer, it runs a hardwired program called bootstrap code that loads the OS.

OS Services • Provides access to software • Gives interface to user • Knows how to load applications into memory • Provides other communication between the user and the application

OS Services • Provides a secure computing environment - Security for a system (logins and passwords) - Security for internal files and functions(You can’t erase my files; A program crash won’t crash the whole computer) - Security from hardware failure (tries to protect you from crashes with backup measures)

OS Services 3. Provides a file system public_html wedding cps1 index.html<HTML>My Homepage images Comp.gif Guestlist Spreadsheet index.html<HTML>My CPS1Homepage Lab 1

OS Services 4. Provides for Multiprogramming (Multitasking) A process is a program in some state of execution. Many can be running at once, while the processor is waiting on one process, it runs a second. Some processes have priority over the others. It may also interrupt a process because of error or just to give another process a chance to run.

More on Multiprogramming OS Print a file Read from Disk Process 2 RegisterValues Disk A Process 3 RegisterValues Disk A Process 1 RegisterValues Printer

More on Multiprogramming • Several programs are competing for processor time, memory, use of devices, etc… • OS is the manager that says who gets what • OS must be programmed to avoid problems…

Dining Philosophers • Dijkstra: 1965 • Setup for thinking about multiple processes sharing resources

Scenario 1: • Everyone must pick up/put down left utensil first and then right utensil • NO grabbing both at same time!!! • Show Deadlock

Scenario 2: • Number around table • Evens: Left, then right (pick up/put down) • Odds: Right, then left (pick up/put down) • NO GRABBING BOTH AT SAME TIME!!! • Deadlock? • Starvation? • Can you make up something better?

Multiprogramming Potential Problems • Starvation – one process never gets the chance to get a resource • Deadlock – every process waiting for something, and none can run • Dirty Data – if more than one process is accessing a piece of data, there can be problems

Data Sharing: Dirty Data x = 4; x = x + 1; print x; Shared integer x x = x + 6;

Conclusion • Operating Systems provide a bridge between user and computer • They give access to computer functionality • They provide security • They provide file systems • They manage multiprocessing and resource allocation

Operating Systems