Chapter 2: Operating-System
Structures
Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013
Chapter 2: Operating-System Structures
● Operating System Services
● User Operating System Interface
● System Calls
● Types of System Calls
● System Programs
● Operating System Design and Implementation
● Operating System Structure
● Operating System Debugging
● Operating System Generation
● System Boot
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Operating System Services
● Operating systems provide an environment for execution of programs
and services to programs and users
● One set of operating-system services provides functions that are
helpful to the user:
● User interface - Almost all operating systems have a user
interface (UI).
4 Varies between Command-Line (CLI), Graphics User
Interface (GUI), Batch
● Program execution - The system must be able to load a
program into memory and to run that program, end execution,
either normally or abnormally (indicating error)
● I/O operations - A running program may require I/O, which may
involve a file or an I/O device
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Operating System Services (Cont.)
● One set of operating-system services provides functions that are helpful to
the user (Cont.):
● File-system manipulation - The file system is of particular interest.
Programs need to read and write files and directories, create and delete
them, search them, list file Information, permission management.
● Communications – Processes may exchange information, on the same
computer or between computers over a network
4 Communications may be via shared memory or through message
passing (packets moved by the OS)
● Error detection – OS needs to be constantly aware of possible errors
4 May occur in the CPU and memory hardware, in I/O devices, in user
program
4 For each type of error, OS should take the appropriate action to
ensure correct and consistent computing
4 Debugging facilities can greatly enhance the user’s and
programmer’s abilities to efficiently use the system
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Operating System Services (Cont.)
● Another set of OS functions exists for ensuring the efficient operation of the
system itself via resource sharing
● Resource allocation - When multiple users or multiple jobs running
concurrently, resources must be allocated to each of them
4 Many types of resources - CPU cycles, main memory, file storage,
I/O devices.
● Accounting - To keep track of which users use how much and what
kinds of computer resources
● Protection and security - The owners of information stored in a
multiuser or networked computer system may want to control use of
that information, concurrent processes should not interfere with each
other
4 Protection involves ensuring that all access to system resources is
controlled
4 Security of the system from outsiders requires user authentication,
extends to defending external I/O devices from invalid access
attempts
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A View of Operating System Services
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User Operating System Interface - CLI
CLI or command interpreter allows direct command entry
● Sometimes implemented in kernel, sometimes by systems
program
● Sometimes multiple flavors implemented – shells
● Primarily fetches a command from user and executes it
● Sometimes commands built-in, sometimes just names of
programs
4 If the latter, adding new features doesn’t require shell
modification
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User Operating System Interface - GUI
● User-friendly desktop metaphor interface
● Usually mouse, keyboard, and monitor
● Icons represent files, programs, actions, etc
● Various mouse buttons over objects in the interface cause
various actions (provide information, options, execute function,
open directory (known as a folder)
● Invented at Xerox PARC
● Many systems now include both CLI and GUI interfaces
● Microsoft Windows is GUI with CLI “command” shell
● Apple Mac OS X is “Aqua” GUI interface with UNIX kernel
underneath and shells available
● Unix and Linux have CLI with optional GUI interfaces (CDE,
KDE, GNOME)
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Touchscreen Interfaces
● Touchscreen devices require new
interfaces
● Mouse not possible or not desired
● Actions and selection based on
gestures
● Virtual keyboard for text entry
● Voice commands.
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The Mac OS X GUI
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System Calls
● Programming interface to the services provided by the OS
● Typically written in a high-level language (C or C++)
● Mostly accessed by programs via a high-level
Application Programming 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)
Note that the system-call names used throughout this
text are generic
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Example of System Calls
● System call sequence to copy the contents of one file to another file
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Example of Standard API
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System Call Implementation
● Typically, a number associated with each system call
● System-call interface maintains a table indexed according to
these numbers
● The system call interface invokes the intended system call in OS
kernel and returns status of the system call and any return values
● The caller need know nothing about how the system call is
implemented
● Just needs to obey API and understand what OS will do as a
result call
● Most details of OS interface hidden from programmer by API
4 Managed by run-time support library (set of functions built
into libraries included with compiler)
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API – System Call – OS Relationship
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System Call Parameter Passing
● Often, more information is required than simply identity of desired
system call
● Exact type and amount of information vary according to OS
and call
● Three general methods used to pass parameters to the OS
● Simplest: pass the parameters in registers
4 In some cases, may be more parameters than registers
● Parameters stored in a block, or table, in memory, and
address of block passed as a parameter in a register
4 This approach taken by Linux and Solaris
● Parameters placed, or pushed, onto the stack by the program
and popped off the stack by the operating system
● Block and stack methods do not limit the number or length of
parameters being passed
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Parameter Passing via Table
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Types of System Calls
● Process control
● create process, terminate process
● end, abort
● load, execute
● get process attributes, set process attributes
● wait for time
● wait event, signal event
● allocate and free memory
● Dump memory if error
● Debugger for determining bugs, single step execution
● Locks for managing access to shared data between processes
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Types of System Calls
● File management
● create file, delete file
● open, close file
● read, write, reposition
● get and set file attributes
● Device management
● request device, release device
● read, write, reposition
● get device attributes, set device attributes
● logically attach or detach devices
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Types of System Calls (Cont.)
● Information maintenance
● get time or date, set time or date
● get system data, set system data
● get and set process, file, or device attributes
● Communications
● create, delete communication connection
● send, receive messages if message passing model to host
name or process name
4 From client to server
● Shared-memory model create and gain access to memory
regions
● transfer status information
● attach and detach remote devices
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Types of System Calls (Cont.)
● Protection
● Control access to resources
● Get and set permissions
● Allow and deny user access
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Examples of Windows and Unix System Calls
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Standard C Library Example
● C program invoking printf() library call, which calls write() system call
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Example: MS-DOS
● Single-tasking
● Shell invoked when system
booted
● Simple method to run
program
● No process created
● Single memory space
● Loads program into memory,
overwriting all but the kernel
● Program exit -> shell
reloaded
At system startup running a program
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Example: FreeBSD
● Unix variant
● Multitasking
● User login -> invoke user’s choice of shell
● Shell executes fork() system call to create
process
● Executes exec() to load program into
process
● Shell waits for process to terminate or
continues with user commands
● Process exits with:
● code = 0 – no error
● code > 0 – error code
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System Programs
● System programs provide a convenient environment for program
development and execution. They can be divided into:
● File manipulation
● Status information sometimes stored in a File modification
● Programming language support
● Program loading and execution
● Communications
● Background services
● Application programs
● Most users’ view of the operation system is defined by system
programs, not the actual system calls
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System Programs
● Provide a convenient environment for program development and
execution
● Some of them are simply user interfaces to system calls;
others are considerably more complex
● File management - Create, delete, copy, rename, print, dump, list,
and generally manipulate files and directories
● Status information
● Some ask the system for info - date, time, amount of available
memory, disk space, number of users
● Others provide detailed performance, logging, and debugging
information
● Typically, these programs format and print the output to the
terminal or other output devices
● Some systems implement a registry - used to store and
retrieve configuration information
Operating System Concepts – 9th Edition 2.27 Silberschatz, Galvin and Gagne ©2013
System Programs (Cont.)
● File modification
● Text editors to create and modify files
● Special commands to search contents of files or perform
transformations of the text
● Programming-language support - Compilers, assemblers,
debuggers and interpreters sometimes provided
● Program loading and execution- Absolute loaders, relocatable
loaders, linkage editors, and overlay-loaders, debugging
systems for higher-level and machine language
● Communications - Provide the mechanism for creating virtual
connections among processes, users, and computer systems
● Allow users to send messages to one another’s screens,
browse web pages, send electronic-mail messages, log in
remotely, transfer files from one machine to another
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System Programs (Cont.)
● Background Services
● Launch at boot time
4 Some for system startup, then terminate
4 Some from system boot to shutdown
● Provide facilities like disk checking, process scheduling, error
logging, printing
● Run in user context not kernel context
● Known as services, subsystems, daemons
● Application programs
● Don’t pertain to system
● Run by users
● Not typically considered part of OS
● Launched by command line, mouse click, finger poke
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Operating System Structure
● General-purpose OS is very large program
● Various ways to structure ones
● Simple structure – MS-DOS
● More complex -- UNIX
● Layered – an abstrcation
● Microkernel -Mach
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Simple Structure -- MS-DOS
● 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
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Non Simple Structure -- UNIX
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
4 Consists of everything below the system-call interface
and above the physical hardware
4 Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a
large number of functions for one level
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Traditional UNIX System Structure
Beyond simple but not fully layered
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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
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Microkernel System Structure
● Moves as much from the kernel into user space
● Mach example of microkernel
● Mac OS X kernel (Darwin) partly based on Mach
● 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
● Detriments:
● Performance overhead of user space to kernel space
communication
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Microkernel System Structure
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Modules
● Many modern operating systems implement loadable 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
● Linux, Solaris, etc
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Solaris Modular Approach
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Hybrid Systems
● Most modern operating systems are actually not one pure model
● Hybrid combines multiple approaches to address
performance, security, usability needs
● Linux and Solaris kernels in kernel address space, so
monolithic, plus modular for dynamic loading of functionality
● Windows mostly monolithic, plus microkernel for different
subsystem personalities
● Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa
programming environment
● Below is kernel consisting of Mach microkernel and BSD Unix
parts, plus I/O kit and dynamically loadable modules (called
kernel extensions)
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Mac OS X Structure
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iOS
● Apple mobile OS for iPhone, iPad
● Structured on Mac OS X, added
functionality
● Does not run OS X applications natively
4 Also runs on different CPU architecture
(ARM vs. Intel)
● Cocoa Touch Objective-C API for
developing apps
● Media services layer for graphics, audio,
video
● Core services provides cloud computing,
databases
● Core operating system, based on Mac OS X
kernel
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Android
● Developed by Open Handset Alliance (mostly Google)
● Open Source
● Similar stack to IOS
● Based on Linux kernel but modified
● Provides process, memory, device-driver management
● Adds power management
● Runtime environment includes core set of libraries and Dalvik
virtual machine
● Apps developed in Java plus Android API
4 Java class files compiled to Java bytecode then translated
to executable than runs in Dalvik VM
● Libraries include frameworks for web browser (webkit), database
(SQLite), multimedia, smaller libc
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Android Architecture
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