CS NOTES.pdf

CS NOTES The Internet & WWW The internet and the world wide web are often used interchangeably, but they are not the same thing. The Internet The internet refers to the global network of computers and other electronic...

CS NOTES The Internet & WWW The internet and the world wide web are often used interchangeably, but they are not the same thing. The Internet The internet refers to the global network of computers and other electronic devices connected together through a system of routers and servers It is the infrastructure that allows us to send and receive information, including email, instant messaging, and file transfers The internet also provides access to other services such as online gaming, video streaming, and cloud computing The World Wide Web The world wide web, or simply the web, is a collection of websites and web pages that are accessed using the internet It was created in 1989 by Tim Berners-Lee, who envisioned it as a way to share and access information on a global scale The web consists of interconnected documents and multimedia files that are stored on web servers around the world Web pages are accessed using a web browser, which communicates with web server to retrieve and display the content URL What is a URL? The URL is a text-based address that identifies the location of a resource on the internet CS NOTES 1  It is the address of a web page, image, video, or any other resource available on the internet Components of a URL A URL can contain three main components: Protocol Domain name Web page / file name The protocol is the communication protocol used to transfer data between the client and the server E.g. HTTP, HTTPS, FTP, and others The domain name is the name of the server where the resource is located It can be a name or an IP address The web page / file name is the location of the file or resource on the server It can contain the name of the file or directory where the resource is located A URL looks like this: protocol://domain/path E.g. https://www.example.com/index.html is a URL that consists of the HTTPS protocol, the domain name "www.example.com", and the file name is "/index.html". Protocols Hypertext Transfer Protocol (HTTP) and Hypertext Transfer Protocol Secure (HTTPS) are the two most common protocols used for transferring data between clients and servers on the internet. Hypertext Transfer Protocol (HTTP) CS NOTES 2  HTTP is the protocol used for transferring data between a client and a server on the internet It is a stateless protocol, meaning it does not store any information about previous requests or responses HTTP operates on port 80 by default and sends data in plain text format, making it vulnerable to interception and manipulation Hypertext Transfer Protocol Secure (HTTPS) HTTPS is a secure version of HTTP that uses encryption to protect data transferred between a client and a server It operates on port 443 by default and uses Transport Layer Security (TLS) or Secure Socket Layer (SSL) to encrypt data HTTPS ensures that data transferred between the client and server is secure, making it harder for unauthorized users to intercept or manipulate data Web Browser A web browser is a piece of software used to access and display information on the internet. Purpose of a Web Browser The main purpose of a web browser is to render hypertext markup language (HTML) and display web pages Web browsers interpret the code in HTML documents and translate it into a visual display for the user Functions of a Web Browser Render HTML This will display the webpage Storing bookmarks and favourites CS NOTES 3  Web browsers allow users to save links to frequently visited websites and access them easily using bookmarks or favourites Recording user history Web browsers record the user's browsing history, allowing them to quickly revisit recently viewed pages Allowing use of multiple tabs Web browsers allow users to open multiple tabs and switch between them quickly and easily Storing cookies Web browsers store cookies, which are small files that contain user preferences and login information for websites Providing navigation tools Web browsers provide navigation tools, such as back and forward buttons and a home button, to help users move between pages Providing an address bar Web browsers provide an address bar, which allows users to enter a URL or search term and navigate to a website or search for information Homepage This is the initial page that appears when the browser is launched The homepage can be customised to display frequently visited websites or specific content Runs Active Scripts These are small programs embedded in web pages that allow interactive content such as animations, videos, and pop-up windows to be displayed Download Files A web browser allows files to be downloaded from the internet, such as documents, images, and software Request Web Pages CS NOTES 4  When you enter a web address in the address bar, the web browser sends a request to the web server to obtain the contents of the web page The server responds by sending the web page to the browser, which displays it on the screen DNS The web browser sends the URL to the DNS, which translates the URL into an IP address, which is used to locate the web server Manages Protocols Web browsers manage the HTTP and HTTPS protocols, which are used to transfer data between web servers and browsers HTTP is used for regular web pages, while HTTPS is used for secure pages that require encryption, such as online banking or shopping sites Web Pages When you type in a URL / click on a link the browser sends the URL to the DNS using HTTP The DNS finds the matching IP addresses for the URL and sends the IP address to the web browser The web browser sends a request to the web server for web pages The web pages are sent from the web server to the browser The browser renders HTML to display web pages Any security certificates are exchanged SSL/HTTPS is used to secure the data which will encrypt any data that is sent Cookies What are cookies? CS NOTES 5  Cookies are small files that are stored on a user's device by a website. They are used for various functions, including: Saving Personal Details Cookies can save personal details which can be used to personalize the user experience. This can include Name Email address Other preferences Tracking User Preferences Cookies can track user preferences such as language settings, font size, and colour scheme, which can be used to customize the website experience Holding Items in an Online Shopping Basket Cookies can hold items in an online shopping cart, so that users can continue shopping or return later without losing their selected items Storing Login Details Cookies can store login details such as usernames and passwords, which can be used to remember users' login credentials and make it easier for them to log in Storing Relevant Purchases Displaying Relevant Adverts Tracking Visitor Statistics Determining whether a visitor to a website is a new visitor or repeat visitor There are two types of cookies: session cookies and persistent cookies. Session Cookies These are temporary and are stored only during a user's browsing session CS NOTES 6  They are used to maintain a user's state or activity during a single session, such as when filling out a form or navigating through a website Persistent Cookies These are stored on a user's device for a longer period, usually for a few weeks to several years They are used to remember user preferences and settings, such as language preferences, login details, and shopping cart items Cookies enhance the user experience and make it more convenient for users to interact with websites. However, cookies can also raise privacy concerns and should be used responsibly by website owners. CS NOTES 7