Transcript hello world - Computer Engineering

Operating Systems
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What is an Operating System?
• A program that acts as an intermediary between a user of a
computer and the computer hardware.
• Operating system goals:
– Execute user programs and make solving user problems
easier.
– Make the computer system convenient to use.
• Use the computer hardware in an efficient manner.
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Computer System Components
1. Hardware – provides basic computing resources (CPU, memory, I/O
devices).
2. Operating system – controls and coordinates the use of the hardware
among the various application programs for the various users.
3. Applications programs – define the ways in which the system
resources are used to solve the computing problems of the users
(compilers, database systems, video games, business programs).
4. Users (people, machines, other computers).
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Abstract View of System Components
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Operating System Definitions
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Resource allocator – manages and allocates
resources.
Control program – controls the execution of user
programs and operations of I/O devices .
Kernel – the one program running at all times (all
else being application programs).
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Simple Batch Systems
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Hire an operator
User  operator
Add a card reader
Reduce setup time by batching similar jobs
Automatic job sequencing – automatically transfers control from one
job to another. First rudimentary operating system.
Resident monitor
– initial control in monitor
– control transfers to job
– when job completes control transfers back to monitor
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Time-Sharing Systems–Interactive
Computing
• The CPU is multiplexed among several jobs that are kept in memory
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and on disk (the CPU is allocated to a job only if the job is in
memory).
A job is swapped in and out of memory to the disk.
On-line communication between the user and the system is provided;
when the operating system finishes the execution of one command, it
seeks the next “control statement” not from a card reader, but rather
from the user’s keyboard.
On-line system must be available for users to access data and code.
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Personal-Computer Systems
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Personal computers – computer system dedicated to a single user.
I/O devices – keyboards, mice, display screens, small printers.
User convenience and responsiveness.
Can adopt technology developed for larger operating system’ often
individuals have sole use of computer and do not need advanced CPU
utilization of protection features.
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Common OS System Components
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Process Management
Main Memory Management
Secondary-Storage Management
I/O System Management
File Management
Protection System
Networking
Command-Interpreter System
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UNIX Versions & Clones
•System V (AT&T)
• AIX (IBM)
•BSD (Berkeley Univ.)
•HP-UX (HP)
•Linux (Linus Torvalds)
•Minix (Tanenbaum)
•OSF (open software foundation)
•SCO (santa cruz operation)
•Solaris (SUN Microsystems)
•XENIX (Microsoft)
•FreeBSD
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UNIX HISTORY
• 1950’s time-sharing invented at Dartmouth & MIT (sys. running only basic)
• MIT System CTSS
• 2nd Generation: MIT, Bell Labs, GE designed MULTICS (Multiplexed
Information Computing Service)
• Ken Thompson from Bell Labs wrote stripped down MULTICS on a discarded
PDP-7. Code was written in assembly language.
• Brian Kernighan – (Bell labs) called the system UNICS (Uniplexed
Information Computing Service). Later this name was changed to UNIX.
• Dennis Ritchie joined the team of Ken Thompson.
• UNIX moved to PDP-11
• B and later C languages were designed/developed.
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UNIX HISTORY
• Thompson and Ritchie rewrote UNIX in C.
• 1974, Thompson and Ritchie wrote a landmark paper on on UNIX.
• Universities started to ask for a copy of UNIX.
• By Mid 80’s UNIX was in widespread use.
• AT&T released first commercial UNIX product : System III which was not
well received.
• AT&T later released System V.
• AT&T decided to concentrate on telephone business. Sold UNIX business to
Novell – 1993.
• Novell sold UNIX biz to Santa Cruz Operation in 1995.
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UNIX HISTORY
• Berkeley Unix (BSD: Berkeley Software Distribution). Introduces many
improvements, networking TCP/IP.
• System V and BSD are major 2 Unix flavors
• IEEE POSIX standard was developed to reconcile these two flavors – took
intersection of these two systems
• POSIX: Portable Operating System IX
• POSIX Idea: A software vendor who writes his a program that uses only
procedures defined in POSIX standard knows that this program will run on
every conformant UNIX system.
• OSF : (Open Software Foundation), IBM, DEC, HP Unix system version
(with X11, Motif etc included)
• OSF gradually vanished
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UNIX HISTORY
• Solaris: (from SUN Microsystems) is based on System V.
• Minix (Tanenbaum) written for educational purposes ’87, 12K lines of code.
• Linux: developed by finnish student Linux Torvalds), first released in ’91.
• Minix has micro-kernel architecture, Linux is monolithic.
• Big famous argument between Tanenbaum & Linus about micro-kernel vs
monolithic operating systems.
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Comparison of some operating system sizes
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Windows Desktop OS Family History
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Windows Vista
2009
Windows 7
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Comparison
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Windows Server OS History
2003
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Windows Server 2003 R2
2008
2009
Windows Server 2008
Windows Server 2008 R2
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Miscellaneous OSs
• NeXTSTEP, OPENSTEP :
-object-oriented, multitasking operating system developed by NeXT
Computer.
• MAC OS:
- Apple computer operating system
- Based on Mach/NextStep/FreeBSD/NetBSD
• iOS: based on Mac OS X, runs on the iPhone, iPod Touch, iPad
• Android
- mobile operating system
- developed by Android Inc. was purchased by Google in 2005
- based upon a modified version of the Linux kernel.
• Symbian :
- Nokia's mobile operating systems for mobile devices and smartphones
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WEB Programming
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HTML
• Hypertext Markup Language
• Identifies the elements of a page so that a browser such as MS Internet
Explorer or Netscape can render that page on the computer screen
• Static page description
• WYSIWYG web page authoring tools
- MS Frontpage
- Dreamweaver
- Home Site
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HTML Example Source
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
</HEAD>
<BODY>
<P> Hello world </P>
</BODY>
</HTML>
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HTML Form Example
<HTML><HEAD>
<TITLE> Hello </TITLE>
</HEAD>
<BODY>
<FORM METHOD="GET" ACTION="http://localhost/cgi-bin/ex.cgi >
<INPUT TYPE="text" NAME="word">
<INPUT TYPE="submit" VALUE="Submit word">
</FORM>
</BODY>
</HTML>
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GET and POST METHODS
• GET method passes form input as part of the URL to the server side
program:
http://www.yahoo.com/cgi-bin/process.cgi?firstname=ali&last=veli
• POST method passes input to the standard input of the server side
program:
firstname=ali
last=veli
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JAVASCRIPT
• Scripting language
• Browser contains Javascript interpreter which processes the commands
in the script
• Processed by client
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Javascript Example Source
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
<SCRIPT LANGUAGE= "Javascript" >
function sayhello()
{
document.writeln("<p> Hello world </p>") ;
}
</SCRIPT>
</HEAD>
<BODY ONLOAD= "sayhello()" > </BODY>
</HTML>
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CSS (Cascading Style Sheets)
• Allow you to specify the style of your page elements (spacing, margins
etc) separately from the structure of your documents (section headers,
body, text, links etc)
• “Separation of Structure from Content” allows greater manageability
and makes changing the style of the document easier.
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CSS Example Source
• inline style (w/o CSS)
<HTML>
<HEAD> <TITLE> Hello </TITLE> </HEAD>
<BODY>
<P STYLE= “font-size: 20 pt” > Hello world </P>
</BODY></HTML>
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CSS Example Source
• css style sheet
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
<STYLE TYPE = “text/css”>
P {font-size: 20 pt }
</STYLE>
</HEAD>
<BODY>
<P > Hello world </P>
</BODY></HTML>
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CSS Example Source
• importing the css file:
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
<LINK REL = “stylesheet” TYPE=“text/css” HREF = “styles.css”
</HEAD>
<BODY>
<P > Hello world </P>
</BODY></HTML>
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XML-Extensible Markup Language
• HTML markup is for displaying information
• XML markup is for describing data of virtually any type
• XML enables creation of new markup languages to markup anything
imaginable (such as mathematical formulas, records etc)
• In XML, new tags can be created
• Data is structured in a hierarchical manner
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XML example
<? xml version = “1.0”>
<person>
<firstname> Ali </firstname>
<lastname> Veli </lastname>
<married> yes </married>
<wife>
<firstname> Ayse </firstname>
<lastname> Mehmet </lastname>
</wife>
</person>
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XML Document Model
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A “document model” is used to enforce structure within a
document
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Two types of document models for XML:
– DTD – Document Type Definition
– XML Schema
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Document models are not required in XML
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Validating Parsers
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A validating parser will check an XML document’s structure
against a DTD or XML Schema
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Documents that conform to a document model are “valid”
Validating parsers will report an error if the document does not
conform to it’s document model, even if it is well-formed
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DTD Example: XML File
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<?xml version=”1.0” standalone=”yes”?>
<emails>
<message num=”a1” to=”joe&#64;acmeshipping.com”
from=”brenda&#64;xyzcompany.com” date=”02/09/01”>
<subject title=”Order 10011”/>
<body>
Joe,
Please let me know if order number 10011 has
shipped.
Thanks,
Brenda
</body>
<reply status="yes"/>
</message>
</emails>
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DTD Example: Internal DTD
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<!DOCTYPE emails [
<!ELEMENT emails
(message+)>
<!ELEMENT message
(subject?, body, reply*)>
<!ATTLIST message
num
ID
#REQUIRED
to
CDATA
#REQUIRED
from
CDATA
#FIXED
“brenda&#64;xyzcompany.com”
date
CDATA
#REQUIRED>
<!ELEMENT subject
EMPTY>
<!ATTLIST
subject
title
CDATA
#IMPLIED>
<!ELEMENT body ANY>
<!ELEMENT
reply
EMPTY>
<!ATTLIST reply
status
(yes | no)
"no">
]>
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XML Schema
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XML Schema specification released by the W3C in May 2001, and
contains two parts:
– Part I - structure
– Part II - data types
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Developed as an alternative to DTD’s and is much more powerful
Features:
– Pattern matching
– Rich set of data types
– Attribute grouping
– Supports XML namespaces
– Follows XML syntax
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XML Schema Example
1 <?xml version=”1.0”?>
2 <message
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xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
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xsi:noNamespaceSchemaLocation = "message_schema.xsd">
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<to>Joe Poller</to>
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<from>Brenda Lane</from>
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<date_sent/>
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<subject>Order 10011</subject>
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<body>
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Joe,
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Please let me know if order number 10011 has
shipped.
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Thanks,
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Brenda
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</body>
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XML Schema Example
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<?xml version=”1.0”?>
<xsd:schema xmlns:xsd=”http://www.w3.org/2001/XMLSchema”>
<xsd:element name=”message”>
<xsd:complexType>
<xsd:sequence>
<xsd:element name=”to” type=”xsd:string”
minOccurs-“1”
maxOccurs=”unbounded”/>
<xsd:element name=”from” type=”xsd:string” minOccurs=”1”/>
<xsd:element name=”date_sent” type=”xsd:date”/>
<xsd:element name=”subject” type=”xsd:string”/>
<xsd:element name=”body” type=”xsd:string”/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
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ASP/PHP
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Javascript is client side scripting language
• ASP/PHP are server side scripting languages
• ASP/PHP process pages on the server and return the results in the form
of HTML source to the client (browser)
• ASP is Microsoft product
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PHP Example 1
<html>
<body>
<?php $db = mysql_connect("localhost", "root");
mysql_select_db("mydb",$db);
$result = mysql_query("SELECT * FROM employees",$db);
printf(“<p>First Name: %s</p>\n",
mysql_result($result,0,"first"));
printf(“<p>Last Name: %s</p>\n",
mysql_result($result,0,"last"));
printf(“<p>Address: %s</p>\n",
mysql_result($result,0,"address"));
printf(“<p>Position: %s</p>\n",
mysql_result($result,0,"position"));
?>
</body>
</html>
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PHP Example 2
<html> <body>
<?php if ($submit) { // process form
$db = mysql_connect("localhost", "root");
mysql_select_db("mydb",$db);
$sql = "INSERT INTO employees (first,last,address,position) VALUES
('$first','$last','$address','$position')";
$result = mysql_query($sql);
echo "Thank you! Information entered.\n";
} else{ // display form
?>
<form method="post" action="<?php echo $PHP_SELF?>">
First name:<input type="Text" name="first"><br>
Last name:<input type="Text" name="last"><br>
Address:<input type="Text" name="address"><br>
Position:<input type="Text" name="position"><br>
<input type="Submit" name="submit" value="Enter information">
</form>
<?php
} // end if
?>
</body> </html>
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PHP-MYSQL PROGRAMMING
MYSQL Commands
CREATE TABLE tablename ( columnname typ modifiers,
columnname typ modifiers,
…..)
SELECT fieldname1, fieldname2,.. FROM tablename WHERE criteria
SELECT fieldname1, fieldname2,.. FROM tablename ORDER BY
fieldname ASC
DSC
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PHP-MYSQL PROGRAMMING
INSERT INTO tablename (fieldname1, fieldname2,…) VALUES
(‘value1’, ‘value2’, … )
UPDATE tablename SET fieldname1=‘value1’, fieldname2=‘value2’
WHERE criteria
DELETE FROM tablename WHERE criteria
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CGI
• Common Gateway Interface
• Protocol to enable running programs on the web server
•These programs produce HTML output which is sent to the client (browser)
•Programs can be written in any language (most popular is PERL)
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PERL
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Practical Extraction and Report Language
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Became popular with CGI programs
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High level – rich and easy to use pattern matching, text processing
operators
• Lots of free PERL modules (packages) are available that make
programming easy:
-networking modules
-Html/XMP parser, CGI modules
• Extremely useful for developing automated pograms that surf the Internet
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Automated Web Page Downloader
#!/usr/local/bin/perl
use LWP::UserAgent ;
use HTML::TokeParser ;
$options{"agent"} = "Mozilla/4.6 [en] (X11; I; SunOS 5.7 sun4u)";
my $agent
= new LWP::UserAgent(%options);
my $request = new HTTP::Request('GET' => $ARGV[0] ) ;
my $response = $agent->request($request) ;
if ( $response->is_success() ) {
print($response->content()) ;
} else {
print("Error: " . $reponse->status_line() . "\n" ) ;
die ;
}
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CGI Life Cycle
• Server receives a request for a CGI program
• Server creates a new process to run the CGI program
• Server passes information to the program:
– via environment variables and standard input.
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CGI – Based Web Server
Main Process
Request for CGI1
Child process for CGI1
Request for CGI2
Child process for CGI2
Request for CGI1
Child process for CGI1
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Problems with CGI
• Expensive to create a process for each request:
– requires time and significant server resources,
– limits the # of requests a server can handle concurrently
• Stateless: No history remembered
– A big problem for web-based development
– Solutions: cookies
– Still expensive
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Problems with CGI
• Once the CGI program starts:
– It cannot interact with the web server
– It takes advantage of the server's abilities once it begins execution
• Reasons: the program is running in a separate process.
• Example, a CGI script cannot write to the server's log file.
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Ways to Improve CGI Performance
• FastCGI
• mod_perl
• Other solutions
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FastCGI
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Developed by a company “Open Market”
FastCGI creates a single persistent process for each FastCGI program
It eliminates the need to create a new process for each request.
See: http://www.fastcgi.com/
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FastCGI
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No need to start multiple processes for different requests for the same
fastcgi program
• Still needs one process for each cgi program.
• It does nothing to help the FastCGI program to interact more closely
with the server.
– Not implemented by some of the more popular servers, i.e.,
Microsoft's Internet Information Server.
• Not very portable
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FastCGI – Based Web Server
Main Process
Request for CGI1
Single Child process for
CGI1
Request for CGI2
Request for CGI1
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Single Child process for
CGI2
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Mod_perl
• Used in the Apache web server
• mod_perl is a module that embeds a copy of the Perl interpreter into the
Apache httpd executable
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Providing complete access to Perl functionality within Apache
CGI scripts are precompiled by the server and executed without forking,
Thus running much more quickly and efficiently.
http://perl.apache.org/
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Server Extension APIs
• Proprietary server extension APIs
for example:
– Netscape provides an internal API called NSAPI
– Microsoft provides ISAPI
– Exist within the main process of a web server
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Server Extension APIs
Advantages
• Using one of these APIs, one can write server extensions that enhance or
change the base functionality of the server
• Allowing the server to handle tasks that were once assigned to external
CGI programs.
• Use linked C or C++ code
– Thus can run extremely fast; and
– make full use of the server's resources.
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Web Server with Server Extension API
Main Process
Request for
ServerExtension1
ServerExtension1
Request for
ServerExtension2
ServerExtension2
Request for
ServerExtension1
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Server Extension APIs
Disadvantages
• Difficult to develop and maintain
• Pose significant security and reliability hazards
– a crashed server extension can bring down the entire server.
• Proprietary server extensions are tied to the server API on a particular OS
– Not very portable
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JAVA
• Introduced by SUN Microsystems
• Object oriented programming language
• Java compiler creates bytecodes that are interpreted by java
bytecode interpreter
• Portable bytecode
• Java can be used to create dynamic content on web pages
• Java applets: are programs that can be embedded in HTML
documents. Browser (i.e. client) executes the applets.
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JAVA Servlets
• A servlet is a server-side version of an applet
• Servlets are executed on the server under the control of web server
• Servlets are called from HTML just as with applets
• Servlet receive a request and returns a response to the client in the form
of an HTML source
• Often used as alternative to CGI programs
• Some advantages:
- CGI programs start, execute and stop providing no way to save
information whereas servlet continue to run (hence capable of saving
information)
- Large set of APIs
- Can be faster than CGI
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Java Servlet Based Web Server
Main Process
Request for
Servlet1
thread
Request for
Servlet2
thread
Servlet1
thread
JVM
Servlet2
Request for
Servlet1
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AJAX Technologies
(Asynchronous Javascript and XML)
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Ajax programming uses combination of :
– XHTML/HTML and CSS for formatting.
– DOM accessed with a client-side scripting language such as
JavaScript to dynamically display and interact with the
information presented.
– XMLHttpRequest object is used to exchange data
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asynchronously with the web server without leaving the
current page
– XML is used for transferring data between the server and
client, (any other format can also be used).
Example: Gmail uses ajax technologies
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Web Services Technologies
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XML-RPC
SOAP
WSDL
UDDI
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XML-RPC
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XML-RPC uses a simple XML application to express function
calls (requests) and returned values (responses) between clients
and servers.
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The heart of an XML-RPC message is the way data is encoded
into XML.
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SOAP
( Simple Object Access Protocol )
SOAP :
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XML based protocol to let applications exchange information over HTTP
Protocol for accessing a Web Service.
A communication protocol
For communication between applications
Provides a format for sending messages
Designed to communicate via Internet
Platform independent
Language independent
Simple and extensible
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SOAP
( Example Request)
<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:body pb="http://www.acme.com/phonebook">
<pb:GetUserDetails>
<pb:UserID>12345</pb:UserID>
</pb:GetUserDetails>
</soap:Body>
</soap:Envelope>
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WSDL
( Web Services Description Language )
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WSDL is a document written in XML which describes a web
service. It specifies the location of the service and the
operations (or methods) the service provides.
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UDDI
( Universal Description, Discovery and Integration )
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UDDI is a directory service where businesses can register and
search for web services.
 UDDI communicates via SOAP
 Web service interfaces in UDDI is described by WSDL
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REST
• Representational State Transfer
• REST is an architecture style for designing networked applications.
•Rather than using complex mechanisms such as RPC or SOAP to connect
between machines, simple HTTP is used to make calls between
machines.
• RESTful applications use HTTP requests to post data (create and/or
update), read data (e.g., make queries), and delete data.
• Despite being simple, REST is fully-featured; there's basically nothing
you can do in Web Services that can't be done with a RESTful
architecture.
Examples:
• http://www.acme.com/phonebook/UserDetails/12345
• http://www.acme.com/phonebook/UserDetails?firstName=John&lastName=Doe
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Dynamic Load Balancing
Web-Server Systems
Client1
Client2
Client3
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Server1
Server2
Server3
Client4
Server4
ClientN
ServerM
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Dynamic Load Balancing
Web-Server Systems
• Client-Based Approach
– Web clients, if they are aware of the Web-server system’s replicated
servers, can actively route requests
– After receiving a request, the Web client selects a node of the web
server cluster and, after resolving the address mapping, submits the
request to the selected node, which is then responsible for responding to
the client.
– Approaches:
• Netscape: wwwi.netscape.com
• Via smart client, e.g java applet
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Dynamic Load Balancing
Web-Server Systems
• DNS-Based Approach
– The cluster DNS—the authoritative DNS server for the distributed Web
system’s nodes—translates the symbolic site name (URL) to the IP
address of one server
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Dynamic Load Balancing
Web-Server Systems
• Dispatcher-Based Approach
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Dynamic Load Balancing
Web-Server Systems
• Server-Based Approach
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Amazon’s Cloud Load Balancing
Service
• Elastic Load Balancing automatically distributes incoming application
traffic across multiple Amazon EC2 instances.
• http://docs.amazonwebservices.com/ElasticLoadBalancing/latest/DeveloperGuide/
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