A This is a commonly encountered problem when installing software on a PC. When creating software, programmers have a choice of program languages to use. You may have heard of some of the more common languages such as Java, C++, and Visual Basic. To the end user, it doesn't generally matter which language the author has written the program in. Most people don't really care as long as the program does its job.

However there is sometimes a catch: programs that have been written in Visual Basic need a special collection of files in order to run on a PC. These are commonly known as "VB runtime files" or "VB dlls". Just to make life difficult, if a program was written in a particular version of Visual Basic, then you will need that version's runtime files. For example, a program written in Visual Basic 4 will need the Visual Basic 4 runtime files. However, these files wonÆt help you run another program that was written in Visual Basic 5 or 6. If you donÆt have the correct set, you will get an error message. There are currently four sets of runtime files: Visual Basic 3, 4, 5 and the recently released 6.

Caption: A missing VB runtime file can stop you in your tracks

So how do you know what you need? First of all, check out the documentation or the software vendor's Web site and see if the files are mentioned. Programmers ù both old and new ù often neglect mentioning these requirements when preparing documentation, so it can be difficult to determine which program needs the runtime files, if at all. The easiest way to find out what you need is to wait until you install a program, try to run it and see if you get an error message. Alternatively, you could install all four groups of runtime files (they are included on our cover CD in the Essentials [freeware] section). The files should be copied to the c:\windows\system directory, but sometimes they come with an installation program that will take care of this for you. Once you have the runtime files on your PC, it is a good idea to leave them there: all four sets will occupy about 8MB of space.

Why donÆt the files come with the program? This is mainly an issue of size. The runtime files are about 1-1.4MB when zipped. This can add to download times on the Internet, or make it difficult to squeeze a program onto a floppy. If a program is just 0.2MB, adding the runtime files can take the size program closer to 1.5MB. Furthermore, once you have the runtime files on your computer, there is no need to have them recopied each time you install a new program, so the authors hope that you can figure out the problem. Since Microsoft developed Visual Basic, it is a bit of a mystery why it never distributed these runtime files with the Windows operating system.

In case you are wondering about the function of runtime files, they act as a real-time compiler. Programs must be in machine code in order to run on a PC. However, a program written in Visual Basic is compiled into "P code". This P code can't run on a PC unless it is translated into machine code by the VB runtime files. This is done "on the fly" each time the program is run. The trade-off is that VB programs will be slower than fully compiled programs, but P code also builds flexibility into the design and programming of VB applications.