Download Week 2 _Operating system File

OPERATING SYSTEM CONCEPTS
AND PRACTISE
SYSTEM PROGRAMS
 System programs provide a convenient
environment for program development and
execution.
 They are divided into several categories :
 File management : These programs create, delete,
copy, rename, print, dump, list, and generally
manipulate files and directories
Status information : Some system ask for time ,
memory space and related status information while
others are complex.
 These programs format and print the output to the
terminal.
 Some systems support registry.
 File modification: There are several text
editors available to create and modify the
contents of files.
 Programming-language support : Compilers,
assemblers, debuggers and interpreters for
common programming languages provided to
user with the operating system.
 Program loading and execution : Once a
program is assembled or compiled, it must be
loaded into memory to be executed
 Communications : These programs provide
the mechanism for creating virtual
connections among processes, users, and
computer systems.
 Most operating systems are supplied with
programs that are useful in solving common
problems or performing common operations.
 Such programs include web browsers, word
processors and text formatters, spreadsheets
known as system utilities or system programs
OPERATING SYSTEM STRUCTURE
 The operating system is a complex structure
and must be properly designed.
 A common approach is to partition the task
into small components rather than have one
monolithic system.
 We must know how the components are
interconnected.
Simple Structure
 Some systems do not have a well defined
structures such operating systems started as
small and then grew beyond scope.
 MS-Dos is an example of such a system which
was designed by few people and grew
popular.
 It was written to provide the most
functionality in least space so it was not
divided carefully.
MS-DOS LAYER STRUCTURE
 In MS-DOS, the interfaces and levels of
functionality are not well separated.
 Application programs are able to access the
basic I/O routines to write directly to the
display and disk drives well separated.
 When user program fails the entire system
crashes
 UNIX is another system that initially was
limited by hardware functionality.
 It consists of two separable parts: the kernel
and the system programs.
 The kernel is further separated into a series of
interfaces
 The kernel provides the file system, CPU
scheduling, memory management, and other
operating-system functions through system
calls.
 This monolithic structure was difficult to
implement and maintain.
LAYERED STRUCTURE
 With proper hardware support, operating
systems can be broken into pieces and that
are smaller systems.
 The operating system can then retain much
greater control over the computer.
 Implementers have more freedom in changing
the inner workings of the system and in
creating modular operating systems
 In top down approach the overall
functionalities are determined
 A system can be made modular in many ways.
 One method is the layered approach, in which
the operating system is broken up into a
number of layers.
 The bottom layer (layer 0) is the hardware; the
highest (layer N) is the user interface.
LAYERED OPERATING SYSTEM
 An layered O.S is implementation of abstract
object made up of data and the operations
that can manipulate data.
 Layer M—consists of data structures and a set
of routines that can be invoked by higher-level
layers.
 Further Layer M consists of data structures
and a set of routines invoked by higher level
structures.
ADVANTAGES OF LAYERED APPROACH
 Simplicity of construction and debugging.
 The layers are selected so that each uses
functions and services of only lower-level
layers.
 The first layer can be debugged without any
concern for the rest of the system.
 If an error is found during the debugging of a
particular layer, the error must be on that
layer.
DRAWBACK OF LAYERED APPROACH
 It involves defining various layers.
 The layered approach is less efficient than the
other approaches.
 While executing a system call each layer adds
overhead to the system call.
MICROKERNEL
 In the mid-1980s, researchers at Carnegie
Mellon University developed an operating
system called Mach that modularized the
kernel using the microkernel approach.
 It structures operating system by removing all
nonessential components from the kernel .
 It implements them as system and user-level
programs.
 This process results into a small kernel
 Main function of Microkernel is
 provide a communication facility between the
client program and the various services that are
also running in user space
 Communication is provided by message
passing
 One benefit of the microkernel approach is
ease of extending the operating system.
 All new services are added to user space and
consequently do not require modification of
the kernel.
 The microkernel provides more security and
reliability
 If a service fails the other parts of operating
system remains untouched.
 Operating system that uses microkernel
approach are:
 Tru64 UNIX provides a UNIX interface to the user,
but it is implemented with a Mach kernel.
 QNX is a real-time operating system that provides
services for message passing and process
scheduling
MODULES
 The best current methodology for operatingsystem design involves using object-oriented
programming techniques.
 This technique creates a modular kernel
 The kernel has a set of core components and
dynamically links.
 This type of strategy uses dynamically
loadable modules and is common in modern
implementation of UNIX
Solaris Modular Approach
 The structure is organized around a core
kernel with seven types of loadable kernel
modules:
Loadable system calls
Scheduling classes
File systems
 Executable formats
STREAMS modules
Miscellaneous
Device and bus drivers
 Allows the kernel to provide core services
 Each core component is separate.
 Each talks to the others over known interfaces.
 The Apple Macintosh Mac OS X operating
system uses a hybrid structure.
VIRTUAL MACHINES
 A virtual machine takes the layered approach
to its logical conclusion. It treats hardware
and the operating system kernel as though
they were all hardware.
 A virtual machine provides an interface
identical to the underlying bare hardware.
 The operating system creates the illusion of
multiple processes, each executing on its own
processor with its own (virtual) memory
(a) Non virtual machine (b) virtual machine
 The virtual-machine concept provides complete
protection of system resources since each virtual
machine is isolated from all other virtual
machines.
 Suitable for research and development.
 System development is done on the virtual
machine, instead of on a physical machine and so
does not disrupt normal system operation.
 The virtual machine concept is difficult to
implement due to the effort required to provide
an exact duplicate to the underlying machine
BENEFITS
 Each virtual machine is completely isolated
from all other virtual machines.
 Two approaches to provide sharing have been
implemented
 System programmers are given their own
virtual machine
 System development is done on the virtual
machine instead of on a physical machine.
EXAMPLES OF VIRTUAL MACHINE
 VMware Architecture

 It is a popular commercial application that
abstracts Intel 80X86 hardware into isolated
virtual machines.
• It runs as an application on a host operating
system such as Windows or Linux.
• It allows this host system to concurrently run
several different guest operating systems as
independent virtual machines.
JAVA VIRTUAL MACHINE
 Java is a popular object-oriented programming
language.
 Java also provides a specification for a Java
virtual machine—or JVM.
 Java program consists of one or more classes.
 For each Java class, the compiler produces an
architecture-neutral byte code output (.class)
file that will run on any implementation of the
JVM.
JAVA VIRTUAL MACHINE
 The JVM is a specification for an abstract
computer, it consists of a class loader and a
Java interpreter that executes the
architecture-neutral byte code.
 The class loader loads the compiled . Class
files.
 The verifier checks that the . class file is valid
Java byte code.
 It automatically manages memory by
performing garbage collection.
 It can be implemented on top of host
operating systems or as a part of web browser.
 In hardware on a chip specifically designed to
run Java programs.
 If the JVM is implemented in software, the
Java interpreter interprets the byte code
operations one at a time.
SYSTEM BOOT
 Operating system must be made available to
hardware so hardware can start it
Small piece of code – bootstrap loader, locates the
kernel, loads it into memory, and starts it
Sometimes two-step process where boot block at
fixed location loads bootstrap loader
When power initialized on system, execution
starts at a fixed memory location
Firmware used to hold initial boot code
OPERATING SYSTEM GENERATION
 Operating systems are designed to run on any
of a class of machines; the system must be
configured for each specific computer site.
 SYSGEN program obtains information
concerning the specific configuration of the
hardware system.
 Booting – starting a computer by loading the
kernel.
 Bootstrap program – code stored in ROM that
is able to locate the kernel, load it into
memory, and start its execution.