Linux as the future kernel of Mac OS

In the early 90's Apple was desperate for a new operating system. Past failures such as Pink and Copland left the company in need of a quick fix. With a lot of money in the bank, they started looking outside the company for a solution. The field was narrowed to NeXT and Be, companies started by ex-Apple employees. In December of 1996 a choice was made, to quote Gil Armelio, "We picked Plan A instead of Plan Be.", marking the return of Steve Jobs to Apple. Few can argue that Apple made the right decision, Apple's success under the leadership of Steve Jobs is legendary. However, the NeXTstep operating system Apple acquired from NeXT needed a lot of work before a transition could be made to satisfy Apple's goal of shipping a modern OS with their hardware. During this transition period, Apple had to decide what pieces of software would make up the new operating system. There would need to be a kernel, a compatibility layer to run old Mac OS software, and a new application framework to replace the Mac Toolbox.

Apple's newly acquired OS, NeXTstep was built on the Mach 3.0 kernel, the same microkernel used by GNU/Hurd. Though by then the Mach kernel was largely abandoned, another kernel, Linux, was gaining support and seeing rapid development. The project at Carnegie Mellon to develop Mach had ended in 1994, two years before Apple acquired NeXT. As early as 1991 papers were published documenting performance issues with the Mach kernel. At the time there was much debate over kernel design, 1992 marked the now famous flame war between Linus Torvalds and Andy Tanenbaum over monolithic vs. microkernel design. Even though Apple got Mach from NeXTstep, it still remained to be seen what kernel Apple would use for their new OS. The higher-level pieces of NeXTstep, such as the Objective-C frameworks, had already been ported to other operating systems in the form of OPENSTEP. Apple's future was not tied to the Mach kernel and other options were being considered.