The era of the monolithic PC applications continued and enhanced the rich heritage inherited from the age of mainframes. The transformation from mainframes to personal computers represented a fundamental shift that moved computer processing power from the hands of the few (mainframe operators) to the hands of the many (anyone with a desktop box).

Along with this transformation came the natural exuberance and freedom of being able to create, sell and share programming solutions to hitherto unknown problems. Thousands of software packages were released for personal computers in the early days.

However, though these early applications were exciting and perhaps more powerful than anything that had come before, the lack of any collaborative systems meant that most applications were built and designed for single users.

There were no real email systems, no multi-user databases, and most prominently, documents were stored locally, or on floppy disks.

From an architectural perspective, such applications were fairly primitive. The reason they were primitive was because they integrated all three application layers into one maintenance-heavy, hard-to-share, and unscalable executable.

Wait a minute!

What are the three layers of an application and why would you want to separate them?