Transcript Chapter2 - OS Strcuture

Operating System Structures
Common System Components
 Due to the complex nature of the modern operating
systems, it is partitioned into smaller component.
 Each component performs a well-defined function
with well-defined inputs and outputs.
Common System Components
 Process Management
 Main Memory Management
 File Management
 I/O System Management
 Secondary Management
 Networking
 Protection System
 User Interface/Command-Interpreter System
Basic OS Organization
 Each manager:
 Works closely with other
managers
 Performs a unique role
 Manager tasks
 Monitor its resources
continuously
 Enforce policies determining:

Who gets what, when, and how
much
 Allocate the resource (when
appropriate)
 Deallocate the resource (when
appropriate)
Process Management
 A process is a program in execution (More about
process in chapter 4)
 A process needs certain resources, including CPU
time, memory, files, and I/O devices, to accomplish its
task.
 These resources are either given to the process when it
is created or when it is running. When the process
completes, the OS reclaims all the resources.
Process Management
 The operating system is responsible for the following
activities in connection with process management.
 Creating and deleting both user and system processes
 Suspending and resuming processes
 Providing mechanisms for process synchronization
 Providing mechanisms for process communication
 Providing mechanisms for deadlock handling
Main Memory Management
 All data in memory before and after processing
 All instructions in memory in order to execute
 Memory management determines what is in memory when
 Optimizing CPU utilization and computer response to users
 Memory management activities include:
 Keeping track of which parts of memory are currently being used and by
whom
 Deciding which processes (or parts thereof) and data to move into and out
of memory
 Allocating and deallocating memory space as needed
File Management
 Computers can store information on several different
types of physical media (e.g. magnetic tap, magnetic
disk, CD etc).
 For convenient use of the computer system, the OS
provides a uniform logical view of information storage.
 A file is a logical storage unit, which abstract away the
physical properties of its storage device.
 Commonly, files represent programs (both source and
object forms) and data.
File Management
 The operating system is responsible for the following
activities in connections with file management:
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Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media
I/O System Management
 One purpose of OS is to hide peculiarities of hardware
devices from the user
 I/O subsystem responsible for
 Memory management of I/O including buffering
(storing data temporarily while it is being transferred),
caching (storing parts of data in faster storage for
performance), spooling (the overlapping of output of
one job with input of other jobs)
 General device-driver interface
 Drivers for specific hardware devices
Secondary Storage Management
 Since main memory (primary storage) is volatile and
too small to accommodate all data and programs
permanently, the computer system must provide
secondary storage to back up main memory.
 Usually disks used to store data that does not fit in
main memory or data that must be kept for a “long”
period of time
 Proper management is of central importance
 Entire speed of computer operation hinges on disk
subsystem and its algorithms
Secondary Storage Management
 The operating system is responsible for the following
activities in connection with disk management:
 Free space management
 Storage allocation
 Disk scheduling
Networking (Distributed Systems)
 A distributed system provides user access to various
system resources.
 Retains user access control
Protection System
 Protection – any mechanism for controlling access of processes or users
to resources defined by the OS
 Security – defense of the system against internal and external attacks
 Huge range, including denial-of-service, worms, viruses, identity theft,
theft of service
 Systems generally first distinguish among users, to determine who can
do what
 User identities (user IDs, security IDs) include name and associated
number, one per user
 User ID then associated with all files, processes of that user to determine
access control
 Group identifier (group ID) allows set of users to be defined and controls
managed, then also associated with each process, file
 Privilege escalation allows user to change to effective ID with more rights
Protection System
 The protection mechanism must:
 Distinguish between authorized and unauthorized
usage.
 Specify the controls to be imposed.
 Provide a means of enforcement.
Command-Interpreter System
Command Line Interface (CLI) or command interpreter
allows direct command entry
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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
 If the latter, adding new features doesn’t require shell
modification
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 as “Aqua” GUI interface with UNIX kernel
underneath and shells available
 Solaris is CLI with optional GUI interfaces (Java Desktop, KDE)
Summary of Functions Provided by OS
A View of Operating System Services
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
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?
Requesting Services from OS
 System Call
 Process traps to OS Interrupt Handler
 Supervisor mode set
 Desired function executed
 Returns to application
 Message Passing
 User process constructs message indicating function (service needed)
 Invokes send to pass message to OS
 Process blocks
 ……
 OS receives message
 OS initiates function execution
 Upon function completion, OS returns “OK”
 Process unblock…
Requesting Services from OS
System Calls
System Calls
C program invoking printf() library call, which calls write() system call
Types of System Calls
 Process control
 File management
 Device management
 Information maintenance
 Communications
 Protection
Examples of Windows and Unix System Calls