The HP 95LX, like any IBM PC or PC-compatible computer, is a "DOS machine." This means that the "operating system" for the 95LX (and other PC-compatible computers) is the Microsoft Disk Operating System (referred to as "MS-DOS" or just plain "DOS").
Computers that use the same operating systems can often run the same software. Application software such as word processors, spreadsheet programs, or database programs are designed to work under a specific operating system.
The MS-DOS operating system serves as the intermediary between the computer's hardware and the software it runs. The "front end" of MS-DOS is what the user sees, and the front end looks the same to all users. For example, the DIR (directory) command in any DOS system lists the files in the current directory. However, DOS has to be customized so that it can run on a particular computer's hardware. For this reason the "back end" of DOS was modified so that it could work with the 95LX.
Other examples of operating systems include the Macintosh System 7, IBM's OS/2, and UNIX. Both Microsoft's Windows environment and the HP 95LX System Manager act as operating systems, but both depend on the MS-DOS being present. Each presents a unique operating environment (or front end) for the user.