Today's windowing systems do not differ much in their basic principles of window management. Almost all systems follow the independent overlapping windows approach, where windows are allowed to overlap each other, operations on windows are performed one at a time, and size and location of each window is independent.
With the typical early 80's display resolution ( ) it was not possible to display two page-sized documents on the screen simultaneously. Overlapping windows came as a solution to the small-screen problem by allowing more windows to be open simultaneously.
Resolutions like are quite common these days, which is roughly four times the 80's resolution. Besides the resolution, graphics processing speed increased as well, which made sophisticated animations feasible. Animations in windowing systems help users to understand the result of operations and decrease the cognitive load.
With advances in computer technology, more demanding applications come into existence. The amount and variety of information that users have to deal with increased a lot with advances in networks and the Internet. The information that is facing the users is usually unorganized and dynamically changing, thus users themselves need to do the organization. Typically when exploring information users want to keep both detail and overview.
Computer-Aided Design (CAD), Computer-Aided Engineering, Object-Oriented Development Environments, and Geographic Information Systems (GIS) are typical multi-window applications. In these applications, it is typically necessary to open many windows displaying simultaneously different parts or representations. Also opening separate windows for toolboxes, commands, and options is becoming the practice in complex applications.
With the increase in the number of windows, visualizing simultaneously all the necessary information for a task became difficult. As the number of windows per task increases, task-switching becomes more time-consuming since more windows need to be opened/closed or moved/resized under the independent overlapping windows approach. Due to the independence of windows, each window must be handled separately. Longer delays due to housekeeping further increase task-completion time because of the loss of users' mental task context, kept in short-term memory. Increase in the number of windows also prevents users to see the overview of their desktop due to overlapping windows. This might delay users to switch to unfinished tasks.
Contents of short-term memory are not only affected by the time that passes, but also by the type of work carried out during that time period. Since window housekeeping is an activity related to the computer domain and not to the users' task , the time spent on window management substantially increases the disruptive effect on the short-term memory, thus implies a non-linear cost curve as the number of windows per task increases.
Gaylin  observed that the number of window operations that are used to switch the active window set constitutes 63% of all the operations in an independent overlapped window manager. This result supports the findings by Bannon et al.  that people switch among tasks frequently forcing them to change the visible set of windows on the screen.
Bederson and Hollan  observed that in traditional window-based systems there is no graphical depiction of the relationship among windows even when there is a strong semantic relationship. This problem is most apparent in hyper-text browsers and CAD systems, where each subwindow is either a link followed or part of the system under design. In current approaches, users have to deal with each window separately when organizing their desktop.
Kahn et al.  observed a similar phenomenon and called the presence of too many open windows ``Windowitis''. They observed that in Windowitis situations the users become quickly disoriented, lose the relationships that exist between windows due to loss of spatial cues, and become unproductive in completing their tasks.
Bly and Rosenberg  characterized the requirements of multi-window systems as the ability of the windows to conform to their contents and the ability of the system to relieve the user of window management.
On the basis of the problems discussed, we have updated these requirements:
Earlier research that addresses some of these is described in the Related Work section at the end of the paper.