The Internet
The Internet is a global network of networks that lets computers around the world communicate using the TCP/IP protocol suite. It evolved from ARPANET, launched in 1969 by the US Department of Defense, into today's public, commercial network of billions of devices.
World Wide Web
The World Wide Web is one application that runs on top of the Internet. It was invented by Tim Berners-Lee in 1989 at CERN. The Web consists of hyperlinked documents (web pages) accessed using browsers via the HTTP protocol. Other Internet services include email (SMTP), file transfer (FTP), and remote login (SSH).
Client-Server Architecture
The Web uses a client-server model:
- Client — a browser (Chrome, Firefox, Safari) that sends requests.
- Server — software (Apache, Nginx, IIS) that listens on port 80/443 and returns responses.
Requests and responses travel as HTTP messages.
HTTP Protocol
HTTP (HyperText Transfer Protocol) is a stateless request-response protocol. An HTTP request includes:
- Method: GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS.
- URL with path and query string.
- Headers (User-Agent, Accept, Cookie, Authorization).
- Body (for POST/PUT).
A response has a status code (200 OK, 301 Moved, 404 Not Found, 500 Server Error), headers, and a body.
HTTPS
HTTPS is HTTP over TLS. It encrypts traffic, authenticates the server with a digital certificate, and protects against eavesdropping and tampering. Modern browsers mark plain HTTP sites as "Not Secure".
URL Structure
A Uniform Resource Locator has the form:
scheme://host:port/path?query#fragmentExample: https://example.com:443/products?id=7#reviews.
DNS
The Domain Name System translates human-friendly names like google.com into IP addresses. Resolution walks through root, TLD (.com), and authoritative name servers. Records include A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), TXT (arbitrary).
IP Addressing
IPv4 addresses are 32 bits written as four dotted decimals (192.168.1.1). IPv6 uses 128 bits in hex groups (2001:db8::1). Private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are used inside LANs and hidden behind NAT.
Web Browsers
A browser has a rendering engine (Blink, WebKit, Gecko) that parses HTML, CSS, and JS, constructs the DOM and CSSOM, computes layout, and paints pixels. Developer tools expose this pipeline.
Web Servers
Popular servers: Apache, Nginx, IIS, Node.js. They serve static files and forward dynamic requests to application code (PHP, Python, Node, Java).
Static vs Dynamic Websites
Static sites serve fixed HTML files (fast, simple, easy to cache). Dynamic sites generate pages on each request using a programming language and database. Modern single-page applications (SPAs) blur the line.
Web Standards and W3C
The World Wide Web Consortium (W3C) develops open standards for HTML, CSS, SVG, XML, and more. The WHATWG maintains the living HTML standard. Following standards keeps pages interoperable.
Summary
The Web is a hyperlinked information space built on the Internet, using HTTP over TCP/IP. Browsers request resources identified by URLs; servers return HTML, CSS, and JavaScript which the browser renders. Understanding this foundation is the first step in web development.
Important Questions
- Differentiate the Internet and the World Wide Web.
- Explain the client-server model with example.
- List five HTTP methods and their purposes.
- What do HTTP status codes 200, 301, 404, and 500 mean?
- Explain the structure of a URL.
- What is DNS? List common record types.
- Differentiate IPv4 and IPv6.
- Differentiate static and dynamic websites.