MSDE (Microsoft Data Engine) is a restricted version of SQL Server that bridges the gap between small single-user programs and large multi-user applications. MSDE is available for free at Microsoft's MSDE home page if you own one of the following Visual Studio products:
Visual Studio 6.0 Professional or Enterprise edition
Visual Basic 6.0 Professional or Enterprise edition
Visual C++ 6.0 Professional or Enterprise edition
Visual InterDev 6.0 Professional or Enterprise edition
Visual J++ 6.0 Professional or Enterprise edition
Visual FoxPro 6.0 Professional or Enterprise edition
MSDE is also included on the Visual Studio .NET CD-ROMs.
Because MSDE is a version of SQL Server, it uses the same architecture as SQL Server (and shown in Figure 2). That means you can upgrade an MSDE application to a full-blown SQL Server application relatively easily. You can build the initial application inexpensively using MSDE. If you later decide that you need the enhanced features that SQL Server provides, you can upgrade with a minimum of hassle.
MSDE looks like Microsoft's plan for the future of small database development, so it's probably worth your effort to learn how to use it. This plan makes sense from Microsoft's point of view because it encourages you to prepare your application for upgrading to the more expensive SQL Server product.
MSDE also makes sense from your point of view. It lets you build an initial application inexpensively while allowing you the later option of upgrading. At the same time, it gives you access to the more sophisticated user access controls provided by SQL Server.