Computers can generally be characterized into two types: ones that are designed to have more than one user attached and those intended for a single user. In the beginning almost all computing was done on large multi-user machines, partly due to their expense, which precluded their use to all but large institutions or wealthy corporations. Mainframes ruled this era and excelled at their role: providing a reliable computing platform for hosting databases, transaction servers, and centralized applications. The interaction was through character-based screens that, while providing fast and efficient green screen access, was to be their Achilles heel.