To the basic PS system, DPS adds a number of features intended to ease working with bitmapped displays and improve performance of some common tasks.
In order to support interactive, on-screen use with reasonable performance, changes were needed: DPS did not, however, add a windowing system.
[citation needed] The developers of NeXT wrote a completely new windowing engine to take full advantage of NeXT's object-oriented operating system.
A number of commands were added to DPS to create the windows and to react to events, similar to but simpler than NeWS.
Apple chose to use this model for a variety of reasons, including the avoidance of licensing fees for DPS and more efficient support of legacy Carbon and Classic code; QuickDraw-based applications use bitmapped drawing exclusively.