The only way to get an MS-DOS computer to do something was to type a command at this prompt and if you can imagine, it was a rather cumbersome way to use a computer. As an example, to load up Microsoft's simple editing program, you had to type the name of the drive that the program was on, the directory that the program was in, and then the name of the program. The network card is similar to the old modems we used in the past to connect to the Internet, however in a home network, it's used to communicate with every computer that's connected to it. You'll want to first, select the computers that will connect to each other and then install the network cards inside each of them. dll - This extension indicates a Dynamic Link Library which may contain additional programming code for software. Many different programs often share Dynamic Link Libraries and you'll find a bunch of them in the Windows/System directory (but don't ever delete them)! .exe - This extension indicates a program or an application like Microsoft Word, Internet Explorer, or Outlook Express. All the drivers of a program are stored onto the computer and used whenever a program is started. Apple's Macintosh computer was among the first of a couple systems to establish a user-to-hardware relationship through a user-friendly interface. Today, we have quite a few operating systems. Some of the more popular ones are Windows Vista, Mac OS X, ZETA, IBM, Unix, and Linux. Traditionally, software is developed behind closed doors. A team of professional coders build it but the community at large isn't part of its conception. It's costly to produce and as you can probably guess, that cost is passed on to the end user: the consumer. Open source software on the other hand is free. We described shareware in another article, but because both commercial software and shareware require payment, they're the target of pirates who seek to make these kinds of programs free to use. Depending on their binding legal agreements, licensing typically allows the use of a single program on a single computer.