ensured. It also allows GUI's to easily be implemented making it easier for the users to access the system. As part of the Client/server model there are two distinct subclasses these are the simple two tier model and the more complex three tier model. The two tier model is aimed at making the use of distributed systems more user friendly by adding better support for Graphical user Interfaces than a mainframe. It also vastly improves the scalability of a system by increasing the number of simultaneous users that can be connected up to 100. In the two tier system the user interface is located on the client while the Database Management System is found on the server. This splits the processing between the machines and takes some of the strain off the server. The database Management system is accessed by the user through the GUI hosted on their local machine and communicates to the server through SQL statements or Call-Level interface. While the system can handle up to 100 users once this figure is breached the system performance seriously degreases due to the 'keep alive' system used on all the connected machines even if they aren't currently doing anything. This is normally used for non complex, non time critical information processing systems.
             Two Tier Client Server Architecture Design [Louis 95]
             The three tier architecture was introduced to attempt to overcome the problems of the two tier system. This introduces a tier between the client and the server. The middle layer can add tasks such as perform queuing, application execution, database staging, scheduling and priorities. This system allows a much larger number of clients to be connected and can easily handle a thousand separate connections without any performance loss. Partitioning the program over multiple servers is also now a possibility and can at times be done by simply dragging and dropping the files onto the required server. Perhaps the o
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