1. Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Chapter 2: Operating-System Structures T.Yang, 2012 Partially based on the OSCE text book

2. Chapter 2: Operating-System Structures Operating System Services & User OS Interface System Calls System Programs (System utilities) Operating System Design and Implementation Virtual Machines

3. A View of Operating System Services

4. Linux Layers

5. Nachos system Layers Base Operating System (Linux for our class) Nachos kernel threads Thread 1Thread 2Thread N Nachos OS modules (Threads mgm, File System, Code execution/memory mapping, System calls/Interrupt) Simulated MIPS Machine (CPU, Memory, Disk, Console) User process Projects 2&3 Project 1

6. OS UI: Shell Command Interpreter

7. OS User Interface: GUI

8. Programming API – OS System Call

9. Standard C Library Example C program invoking printf() library call, which calls write() system call

10. System Calls System calls: Programming interface to the services provided by the OS Mostly accessed by programs via a high- level Application Program Interface (API) rather than direct system call use Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM) Why use APIs rather than system calls?

11. System Calls System calls: Programming interface to the services provided by the OS Mostly accessed by programs via a high- level Application Program Interface (API) rather than direct system call use Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM) Why use APIs rather than system calls? Portability. Simplicity.

12. Types of System Calls Process control File management Device management Information maintenance Communications Protection

13. Examples of Windows and Unix System Calls

14. Transition from User to Kernel Mode

15. Unix I/O Calls fileHandle = open(pathName, flags) A file handle is a small integer, valid only within a single process, to operate on the device or file Pathname: a name in the file system. In unix, devices are put under /dev. E.g. /dev/ttya is the first serial port, /dev/sda the first SCSI drive Flags: read only, read/write, append etc… Mode may be added as the third argument for file permission errorCode = close(fileHandle) Kernel will free the data structures associated

16. Unix I/O Calls byteCount = read(fileHandle, buf, count) Read at most count bytes from the device and put them in the byte buffer buf. Bytes placed from 0 th byte. Kernel can give the process fewer bytes, user process must check the byteCount to see how many were actually returned. A negative byteCount signals an error (value is the error type) byteCount = write(fileHandle, buf, count) Write at most count bytes from the buffer buf Actual number written returned in byteCount A negative byteCount signals an error

17. 17 Copy file1 to file2 #command syntax: copy file1 file2 #include #define BUF_SIZE 8192 void main(int argc, char* argv[]) { int input_fd, output_fd; int ret_in, ret_out; char buffer[BUF_SIZE]; /* Create input file descriptor */ input_fd = open (argv [1], O_RDONLY); if (input_fd == -1) { printf ("Error in openning the input file\n"); return; }

18. 18 copy file1 file2 /* Create output file descriptor */ output_fd = open(argv[2], O_WRONLY | O_CREAT, 0644); if(output_fd == -1){ printf ("Error in openning the output file\n"); return; } /* Copy process */ while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){ ret_out = write (output_fd, &buffer, ret_in); if(ret_out != ret_in){ /* Write error */ printf("Error in writing\n"); } close (input_fd); close (output_fd); }

19. System Programs/Utilities Categories of System programs/utilities Process status and management File /directory manipulation File modification and text processing Programming language support (compilers) Program loading and execution Communications Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls

20. Linux Utility Programs

21. OS Design & Implementation Start by defining goals and specifications Affected by Choice of hardware User goals – convenient to use, easy to learn, reliable, safe, and fast System goals – easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

22. OS Design Principles Separate policy (what to do) and mechanism (how to do) Why? Layered structure Modular Monolithic kernel vs. Microkernel Maximize flexibility

23. Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

24. MS-DOS: Simple Layer Structure written to provide the most functionality in the least space

25. Traditional UNIX System Structure

26. Modular approach Object-oriented Each core component is separate Each talks to the others over known interfaces Each is loadable as needed within the kernel

27. 27 Monolithic Kernel vs. Microkernel

28. Microkernel System Structure Moves as much from the kernel into “user” space Communication takes place between user modules using message passing Benefits: Easier to extend a microkernel Easier to port the operating system to new architectures More reliable (less code is running in kernel mode) More secure Weakness: Performance overhead of user space to kernel space communication

29. Mac OS X Structure

30. Virtual Machines A virtual machine takes the layered approach A virtual machine provides an interface identical to the underlying bare hardware. The host creates the illusion that each guest has its own processor and virtual memory/storage.

31. Virtual Machines (Cont.) (a) Non-virtual machine (b) virtual machine

32. VMware Architecture

33. The Java Virtual Machine

34. New OS Interface for Applications Google Android Microsoft Windows Phone 7Apple iOS Application StoreAndroid Market App MarketplaceAppStore User Interface Java Application FrameworkSilverlightCocoa BrowserWebkit Internet ExplorerWebkit 3D GraphicsOpenGLDirectXOpenGL Main programming languageJavaC#Objective-C Virtual machineDalvik VMCLRNone

35. Android (Linux-based)

36. Apple iOS Unix-based