How the Internet Works
There are two levels to the internet/WWW scenario. The hardware level is the Internet itself and provides a path (highway) upon which our data can travel known as TCP/IP. Many different applications that manage and present the data comprise the second level.
The Internet is a world wide system of computers that are all tied together through the telephone system. The drawing shows a dial-up scenario in which the entry point for an individual would be at the service providers modem. Within this context all public data is available at all times to be served across the internet backbone or out through an attached modem. This data is served through TCP/IP (Transmission Control Protocol/Internet Protocol) and the brand or operating system of any individual piece of equipment is not relevant as it must be TCP/IP compatible to be a part of the network. The location of a particular computer or file is also irrelevant since the equipment is all interconnected in a way that serves up the linked data just as though it was all comming from one computer.
The data in your PC is private
All data that is outside of this entry point at your service providers modem, (in your PC) is not public and can not be accessed unless you are running software that specifically allows this access. If your connection is through a local service provider and you are using standard commercial software in your PC no one can see any data within your PC environment without your knowledge.
It is possible however for a specific software set to be designed so that when running on both ends of the connection it could look at your private data. This would certainly be un-ethical and perhaps illegal unless you had specificially given your permission.
SLIP and PPP dial-up connections
Your computer is connected through your modem using SLIP (Serial Inline Protocol) or PPP (Point-to-Point Protocol) and is managed along with the local TCP/IP stack by the program that dials the phone through your modem. CSLIP uses data compression for faster transmission.
The connection is complete
Once your modem has connected and the dialer has logged on to your service providers computer the hardware level is complete, you are an interactive part of the Internet.
Now that all matters concerning the format and protocol for data transfer have been resolved, this level provides the interface between you and the data to be handled. Our first thought when we think about the Internet is surfing the World Wide Web and this task is handled with a browser.
Your browser - Surfing the Web
The original graphical browser, Mosaic, was developed at NCSA (The National Center for Super Computing Activities) at The University of Illinois in Urbana. The source code for Mosaic is free and available to anyone for use in developing their own variation. Mosaic has undergone a number of revisions and is in use by millions of users worldwide today. Netscape, on the other hand, was introduced in early 1995 by a company that was formed by people from the original Mosaic project. The purpose of that new company was to produce a commercial browser that would be sold on the open market. Published estimates state that Netscape holds 70 percent of the market as 1995 draws to a close.
Regardless of the brand, the browser has the task of requesting the specific data that you wish to view and displaying it correctly. This sounds simple but it is not. The browser must render text according to the specification within the HTML incoded file but it must also account for the display capabilities of the client computer and make the necessary adjustments. And that only covers text. As images are encountered in the data stream the browser must also be able to render each type at the best quality that the client can handle.
HTML - Hypertext Markup Language
The http: at the beginning of most Web addresses designates to the browser that the data format used there is HTML. Hypertext markup language is a system for marking up documents with a set of tags that designate the design and display intention of the author and how sections or documents are linked together. It is the responsibility of the browser to approximate the wishes of the author as the document is displayed. The capability of the client hardware and preferences the viewer must also be considered by the browser. An HTML author can express his display wishes with HTML tags but can never be certain how the page will be displayed in a specific environment.
FTP - Transferring files
As your browser handles display data an FTP (File Transfer Protocol) program manages data that you simply want to move from one place to another. Since FTP will not display the data it can handle any file format, including program files.
Telnet - Terminal emulator
There may be times when you want to become a client on a distant machine at the operating system level of that machine. On a UNIX computer that would be at the command prompt level. Telnet is the most popular terminal emulator on the Internet today.