Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Operating Systems Lecture 4 System Calls OS System Structure

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Computing Environments Traditional Computing Client-Server Computing Peer to Peer Computing (e.g. Napster) Web-based Computing Special Purpose Systems:  Embedded Systems  Multimedia Systems  Handheld Systems Operating System Concepts Client Server Computing

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, User-Operating System Interface Command Line Interpreter (CLI) (e.g. UNIX or MS-DOS)  Fetches command from user and executes  Commands may be built into O.S. or names of programs to execute. Operating System Concepts Bourne Shell Command Interpreter for Solaris

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, User-Operating System Interface--GUI GUI uses desktop metaphor with Icons for files and folders. Actions executed with mouse-over and button-clicks. Many systems provide both CLI and GUI (e.g. LINUX has desktop environment, Apple UNIX shell, Windows has CLI shell). Operating System Concepts Mac OS X GUI

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts System Calls System calls provide the interface between a running program and the operating system.  Generally available as assembly-language instructions.  Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++)  Use API's so don't need to know system details. (Win32, POSIX, Java)

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts System Calls are Used Frequently A single program may make numerous system calls. For example, a program to read from one file and write to another would need system calls for the following: (We will discuss this in class)  Prompt the user to enter file names  Read in filenames  Open input file  Read from input file  Open/create output file  Write output to file  Close input and output files The system must be able to signal and handle errors that occur.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts C program invoking printf() library call, which calls write() system call API system call

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Passing Parameters Three general methods are used to pass parameters between a running program and the operating system.  Pass parameters in registers.  Store the parameters in a table in memory, and the table address is passed as a parameter in a register.  Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Passing of Parameters As A Table

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Types of System Calls Process control  create (fork), execute (exec), wait, end (exit), abort (kill), etc. File management (Can you think of any in Linux?)  create (mkdir), delete (rm, rmdir), open, close, read, write, cp, rm, mkdir, rmdir, ls, cat, more, grep, etc. get/set file attributes Device management  read, write, attach (mount), detach (unmount), get/set device attributes Information maintenance  get/set time or date, get/set process/device attributes (getpid, du, ps, etc) Communications  send, receive, connect, accept, get/set status information, gethostid/sethostid, gethostbyname, etc. Protection (Can you think of any?)  get/set file attributes (chmod, chown, chgrp)

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Process Control A process executing one program may want to load and execute another program (e.g. the shell loads and executes programs). The following are important considerations: Where does control return when the new process is finished?  If return control to existing program, must save memory image of existing program before loading new process.  If both programs are to run concurrently, the new process is added to the multiprogramming set of processes. Controlling execution of the process:  get/set process attributes, terminate process Waiting for the process to finish  wait event, signal event Terminating the process  Normal (exit) or abnormal (abort) termination. There are multiple ways of implementing process control.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts MS-DOS Execution At System Start-up Running a Program MS-DOS runs the command interpreter on startup. It loads a new program into memory, writing over part of the interpreter. When the program terminates, the part of the interpreter not overwritten begins execution. It loads the rest of the interpreter from disk.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts UNIX Running Multiple Programs UNIX runs the shell on startup. To start a new process, it uses the fork command to create the process and exec to execute it. If the process is in the foreground, the shell waits for the process to finish. If the process is in the background, the user can continue to issue commands while the process is running. When the process is finished, it executes an exit system call.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, System Calls--Communication Operating System Concepts How is inter-process communication achieved?  Message Passing (think USPS): Good for small amounts of data No conflicts (i.e. with protection and synchronization) Easier to implement  Shared Memory Speed Convenience Both are common and most systems have both.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Message Passing Processes use message passing to send messages to one another. First, the connection must be opened.  The name of the communicator must be known (host name or host id, process name or process id). Use get process id or get host id.  open connection, close connection The recipient uses "accept connection" The initiator is the client. The recipient of the request is the server. Exchange of information made with write message system calls.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Shared Memory In memory sharing, processes communicate by writing and reading to the same memory addresses. Processes use map memory system calls to access memory owned by other processes. Both processes must agree to remove O.S. memory restriction so that they can access the same region of memory. The processes are responsible for the form and location of the data. The processes are responsible for making sure that they are not writing to the same memory area simultaneously.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Communication Models Msg Passing Shared Memory Communication may take place using either message passing or shared memory.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts System Programs System programs provide a convenient environment for program development and execution. The can be divided into:  File manipulation (copy, delete, rename, print, list)  Status information (get date, disk usage, performance info)  File modification (text editors)  Programming language support (compilers, interpreters, debuggers)  Program loading and execution (loaders, linkers)  Communications (IM, , remote login)  Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Types of OS Structure Operating System Concepts The design of operating systems has evolved over time. We can roughly divide them into the following categories: 1.Monolithic systems (1st operating systems). 2.Modular systems (e.g. early UNIX, Solaris) 3.Hierarchical layered systems (e.g. OS/2) 4.Microkernel systems (e.g. Mach) 5.Virtual Machines

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, From monolithic to modular Operating System Concepts Monolithic systems:  No structure to speak of.  As the OS grows, the complexity becomes overwhelming.  Example: OS/360 version 1  created by 5000 programmers over 5 years.  In 1964, had over 1 million lines of code.  Example: Multics  In 1975, had over 20 million lines of code.  When UNIX was written, people joked it was EUNUCHS, i.e. a castrated Multics Modular systems:  Divide OS into modules.  Example: Original UNIX had 2 modules.  System programs (e.g. emacs, compiler)  The kernel (HUGE!)--file system, CPU scheduling, memory management, etc.  Problem: Kernel so big and complex that it was hard to work with and extend.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts MS-DOS System Structure MS-DOS – written to provide the most functionality in the least space  not divided into modules  Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts MS-DOS Layer Structure

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts UNIX System Structure UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts.  Systems programs  The kernel  Consists of everything below the system-call interface and above the physical hardware  Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts UNIX System Structure

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts 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. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers. Advantage: Modularity makes it easy to modify and extend. Disadvantage: Some functions may depend on one another, making a strict hierarchy difficult to implement.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts An Operating System Layer

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts OS/2 Layer Structure Jointly developed in the mid 1980's by IBM and MS

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Modules Operating System Concepts  Most modern operating systems implement kernel modules Uses object-oriented approach Each core component is separate Each talks to the others over known interfaces Each is loadable as needed within the kernel  Overall, similar to layers but with more flexible

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Solaris Modular Approach Operating System Concepts

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Microkernel System Structure Moves as much from the kernel into “user” space. Communication takes place between user modules using message passing. Only the kernel is machine/device dependent. Example: Mac OS X is based on the Mach micro kernel.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Microkernels—Benefits and Drawbacks Operating System Concepts Microkernels:  Advantages:  Modularity (Easy to modify modules)  Extensibility (Can easily add new functions--user processes)  Flexibility (Can remove functions that are not needed)  Portability (Only the small kernel has hardware specific code)  Distributed System support (Message passing can generalize to network communications)  Object oriented (A good design).  Disadvantages: (will discuss in class)  Performance: create/send receive message takes longer than a system call. Efficiency still a problem.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Virtual Machines Virtual Machines:  Provides software interface identical to underlying bare hardware.  Virtual CPU, Virtual Device drivers, Virtual memory, etc.  Each process has its own virtual machine  Implementation provides interface between virtual machine and real machine.  Physical resources divided up between the virtual machines (e.g. minidisks).  Advantages: (will discuss in class)  Security (no process has direct access to system resources.)  System development (Can use virtual machine to test new OS)  System compatibility. Can run Windows on Virtual PC on Mac.  Java runs on Java virtual machine--cross platform.  Disadvantage: (will discuss in class)  Speed: Each instruction is interpreted. This is slower than a direct system call.

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Virtual Machine Diagram Non-virtual Machine Virtual Machine

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, VMWare Architecture Operating System Concepts

Silberschatz, Galvin and Gagne  2002 Modified for CSCI 346, Royden, Operating System Concepts Java Virtual Machine Compiled Java programs are platform- neutral bytecodes executed by a Java Virtual Machine (JVM). JVM consists of - class loader - class verifier - runtime interpreter Just-In-Time (JIT) compilers increase performance