<Section 2.2> The Three Worlds of the Known Internet
The Internet, like ancient Gaul, is divided into three parts. These parts are not so much territories as worlds, each with their own sets of assumptions, favorite dialects, and favored equipment. We may conveniently refer to them as the "PC world", the "UNIX world", and the "Mainframe world". Here's a dossier on each of the three worlds:
World: Personal Computer (PC)
Typical Equipment: IBM PC and clones (85%) , Macintosh (15%)
Conventional Operating Systems: MS-DOS, OS/2
Windowing Systems: Windows, MacOS
Typical Size: PC ($1k to $5k typical; few $100 used)
Clientele: Mixed—Business, Home users, just about everybody
World: (mostly UNIX) workstation
Typical Equipment: Sun Workstation, VAXStations, other vendors
Conventional Operating Systems: UNIX (two major dialects), VMS
Windowing System: X Windows
Typical Size: Workstation ($5k and up)
Clientele: Engineering/Scientific users; more and more businesses
World: Mainframe or Minicomputer
Typical Equipment: IBM (various), Digital Equipment VAXes
Conventional Operating Systems: VM, VMS, UNIX
Windowing Systems: X Windows, if available
Typical Size: Minicomputer or Mainframe ($10k to millions)
Clientele: Big Business, Universities, Government
The neat picture of three worlds is distorted somewhat by a tendency for each of the worlds to have two (or a few) major options, either in choice of equipment, operating system, or vendor. So, for example, the PC world is split into two camps, the MS-DOS people and the Mac people. Similarly, the UNIX world is split into the "BSD" workstations and "System V" (i.e. "5") workstations.
The three worlds are reflected somewhat in networking. The Internet is dominated by minicomputers and workstations running UNIX and VMS, with an ever increasing influx of PCs running MS-DOS and Macs. Machines running other operating systems often put a "UNIX-like" foot forward, so the user can almost believe he or she is dealing with UNIX machines. There is a certain sense that the UNIX software is the standard for the Internet. Software tends to appear on UNIX machines first and then be "ported" to other machines.
What makes it possible for all these disparate machines to talk to each other is the "Internet Protocol" (known more formally as TCP/IP, for Transport Control Protocol/Internet Protocol). TCP/IP can be thought of as a set of rules for two computers to use when they communicate with each other, even if they are not from the same vendor.
We are used to thinking of computer systems as having "software" and "hardware", but it is closer to the truth to say that complicated systems like the Internet have many levels—in the case of the Internet as many as seven—ranging from "very software" to "very hardware". Each level has its own set of rules, called its protocol. The TCP/IP protocol belongs to two of the middle levels. At the moment, the most common protocol for the two most "very hardware" levels is "Ethernet" (looks rather like the coaxial cable used for cable TV), while the "very software" levels are completely dependent on the vendor. In fact, it is this profusion of levels which lets the Internet work on just about any kind of hardware and with software from many different vendors.
Anyway, the Internet grew up as several medium-sized networks, all having diffent "very hardware" and "very software", but using the TCP/IP protocol for their middle layers, were connected together. Two of the first, and biggest, nets to adopt the Internet Protocol were ARPAnet— Internet was first designed for this one—the network for what used to be called DARPA (the Defense Advanced Research Projects Agency of the U.S. Department of Defense), and NSFnet, a network connecting universities and government laboratories for the U.S. National Science Foundation. These and other large networks form the "backbone" of the Internet. But today there are hundreds of smaller nets hooked on to the backbones.