Mac OS X Server 1.x

Mac OS X Server 1.x is the first operating system commercially released by Apple to be based on NeXT technology. It is based on the Rhapsody project, which was previously met with negative reactions by software vendors regarding its intention to run all existing classic Mac OS code in a virtual machine, requiring a large rewrite of applications in order to run natively.

Development
The Rhapsody project was announced in January 1997 at MacWorld Expo and was demonstrated at the 1997 Worldwide Developers Conference (WWDC). Rhapsody represented the fifth major version of the UNIX-based system NeXTSTEP following Apple's acquisition of NeXT. Rhapsody was originally intended to offering a migration path to a new generation of Mac-based operating systems while retaining backward compatibility with classic Mac OS software. This process would be related to Apple's previous Copland project. Rhapsody was intended to release to developers in late 1997 and see public release a year later.

Two developer releases of Rhapsody were released during the time, with both builds being compatible with PowerPC and x86 computers. Rhapsody notably included an emulator under the name of "Blue Box" that would run an emulated session of a classic Mac OS 8 system to run classic applications, while native applications were ran under NeXTSTEP's object libraries known as the "Yellow Box". During development, Apple was contacted by Dell to license distribution of Rhapsody on their PCs, but declined due to inability to get all manufactured computers dual-booted with Rhapsody and Windows for customer preference (reducing Dell's royalty costs to Apple). The Rhapsody builds were critically backlashed by software developers, owing that all classic applications were to be rewritten from scratch to support the native libraries.

Following the backlash, the project would be announced to be changed to a server-released operating system at the 1998 MacWorld Expo, while Apple developed a new API called Carbon, aiming to port the legacy Mac-based libraries under the native Unix API instead of under emulation. The "Yellow Box" layer would later be known as Cocoa. Support for x86 systems would be dropped during the development of the reworked Rhapsody server system. Mac OS X Server 1.0 would ship to the public on 16 March 1999, and was supported by Apple until 2001. During the system's lifespan, an updated version supporting G4 systems would be released. Mac OS X Server 1.0 would be the first version to feature NetBoot.

The codebase of NeXTSTEP would provide the basis of the Darwin operating system, which would develop the core underlying for Mac OS X. The creation of the Carbon API would be incorporated into Mac OS X Public Beta, which would be officially see public release in Mac OS X Server 10.0.

Version branding
Each build of Mac OS X Server 1.x would refer itself as Rhapsody in the kernel, even past the Rhapsody developer releases.