Description
The API OpenStep contrasts with the earlier NeXTSTEP primarily in five ways:
- OpenStep describes only the upper-level libraries and services (like Display PostScript), whereas NeXTSTEP referred to both these libraries and the operating system as well.
- Any code depending entirely on the Mach kernel was removed, so that OpenStep could be run on top of any reasonably powerful operating system.
- A significant amount of effort was put into making the system "endian-free", an issue NeXT had already faced during a port of NeXTSTEP to the Intel platform.
- Low-level objects such as strings were represented with C data types in NeXTSTEP, whereas in OpenStep a number of new classes (NSString, NSNumber, etc.) were introduced to support endian-conversion as well as provide added functionality and become platform-independent. This had ripple-effects throughout the API, mostly for the better. This set of classes (a framework) was called the Foundation Kit, or just Foundation for short.
- OpenStep uses reference counting to manage memory and object lifetimes, and provides Autorelease Pools as a form of automatic memory management. NeXTSTEP does not provide reference counted memory management.
The API specification itself is composed of the two main sets of object-oriented classes: the GUI and graphics front-end known as the Application Kit, and the aforementioned Foundation Kit.
However, OpenStep also specified the use of Display PostScript, a versatile and powerful PostScript-based method of drawing windows and graphics on screen. NeXT, with its devotion to implementing object-oriented solutions, supplied pswraps for interfacing C code to Display PostScript. pswraps acted in an encapsulative way and was somewhat object oriented. The Application Kit, Foundation, and Display PostScript comprise the three key technologies in the OpenStep specification; however, Display PostScript was featured in older NeXT technologies, such as NeXTSTEP.
Read more about this topic: OpenStep
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