Web 101
To understand Web pages, consider:
How Browsers Work
Your Web browser (Netscape Communicator or Internet Explorer, for example) communicates with a server (http://www.lls.edu, for example), which "serves" Web page files back to the browser. Each time you enter a URL or click a link, a new page is served to your computer.
Your browser assembles and displays the pages for use on your computer screen. Different browsers display pages differently, and even different versions of browser display pages differently. Additionally, the type of computer screen and size of the display affect how you see a Web page. So while the server may send the same Web page to everyone, they all will see slight differences.
Web page developers often work with a "lowest common denominator" -- a set of minimum standards that are reliably displayed on most computers using most types of browsers. Sometimes, alternatives are offered, such as a link to a text-only version of the page.
Careful developers test their pages on as many of the browsers and platforms as possible to ensure that they communicate effectively.
How Web Pages Work
A single Web page consists of several files: the HTML contains the text, formatting and layout information; images such as pictures or logos are separate files (usually GIF or JPEG format). This page, for example, has two parts: the HTML contains the text, layout and formatting; and the blue button in the upper left corner of the page is a GIF image.
When you request a page, the browser forwards the request to the appropriate server (see "How the Web Works" for more), and waits for the reply. If the server replies by sending an HTML page, the browser sets to work displaying it. It uses the text, formatting and layout information in the HTML as well as its own formatting rules and the settings of your computer to build the page.
As the browser works through the HTML, it may encounter a reference to an image file. Since images are separate files, the browser sends another request to the server and waits for the image to come back. When it does, the browser adds it to the page based on the HTML page layout (and, of course, the browser's own layout rules and your computer's settings).
How Graphics Work
Web pages commonly use two graphic formats: GIF and JPEG. The major Web browsers have been programmed to display these formats on your screen. JPEG files are used for photos. GIF files are usually used for illustrations, logos, buttons and other elements. Newer browsers may also be programmed to display other formats, such as PNG.
However, graphics display is dependent on the client's computer and computer screen. Most PCs and Macs are able to display thousands of different colors; however, if a color cannot be displayed on a computer, the computer will attempt to a "safe" palette of colors
How the Web Works
Technically, the Internet is a world-wide network -- a mass of wires and routers that allow computers to communicate. The Web uses this world-wide network, as does e-mail, to send and receive information.
On the Web, there are servers and there are clients (PCs equipped with browsers). Each server is identified with a unique number and a unique name (such as www.lls.edu -- known as a domain name), so that requests can be routed to it from anywhere on the system. Each client also uses a unique number for routing, but that number might change each time you log in.
More on the Web
The Web was originally designed to be "stateless" -- that is, that communication occurs in short bursts of activity that do not require constant connections between two specific machines. Basically, the server sits around doing nothing, waiting for a request. Your browser makes a request ("I am computer x, send me file 'index.html'"), the server responds ("Here's the page, have a nice day"), then breaks the connection and goes back to waiting. Next time your browser makes a request, it occurs as a separate transaction ("I am computer x, send me file 'logo.gif'" -- "Here's the page, have a nice day"). And so on. The server logs all these requests, and later
This stateless arrangement is great for processing many requests, since the server doesn't have to remember everyone -- it simply responds to each request as it comes in, then moves on. However, it causes other problems which are important for security, transactions and workflow. As a result, browsers and servers have evolved to include tools to imitate stateful activity. Cookies, certificates, secure connections, and virtual private networks (VPNs) can be used to provide continuity.