formats rather than converting them to PostScript first. When PostScript support is needed for such a printer, Ghostscript can be used. There are also a number of commercial PostScript interpreters, such as TeleType Co.'s T-Script. Use as a display system PostScript became commercially successful due to the introduction of the graphical user interface (GUI), allowing designers to directly lay out pages for eventual output on laser printers. However, the GUI's own graphics systems were generally much less sophisticated than PostScript; Apple's QuickDraw, for instance, supported only basic lines and arcs, not the complex B-splines and advanced region filling options of PostScript. In order to take full advantage of PostScript printing, applications on the computers had to re-implement those features using the host platform's own graphics system. This led to numerous issues where the on-screen layout would not exactly match the printed output, due to differences in the implementation of these features. As computer power grew, it became possible to host the PS system in the computer rather than the printer. This led to the natural evolution of PS from a printing system to one that could also be used as the host's own graphics language. There were numerous advantages to this approach; not only did it help eliminate the possibility of different output on screen and printer, but it also provided a powerful graphics system for the computer, and allowed the printers to be "dumb" at a time when the cost of the laser engines was falling. In a production setting, using PostScript as a display system meant that the host computer could render low-resolution to the screen, higher resolution to the printer, or simply send the PS code to a smart printer for offboard printing. However, PostScript was written with printing in mind, and had numerous features that made it unsuitable for direct use in an interactive display system. In particular, PS was based on the idea of collecting up PS commands until the showpage command was seen, at which point all of the commands read up to that point were interpreted and output. In an interactive system this was clearly not appropriate. Nor did PS have any sort of interactivity built in; for example, supporting hit detection for mouse interactivity obviously did not apply when PS was being used on a printer. When Steve Jobs left Apple and started NeXT, he pitched Adobe on the idea of using