The basic idea is that each application gets its own pool of memory (RAM), whereas on Mac OS 9, there was one giant system-wide pool of memory, shared by all applications.
The reason is that Mac OS X enforces memory protection. Under normal circumstances, individual apps on Mac OS X cannot cause a kernel panic. “Kernel panic” is a fancy term, but the end result is just as disastrous as an old-fashioned system-wide crash - your only option is to reboot, and hope that you didn’t have anything important open with unsaved changes. But that’s not to say Mac OS X can’t be brought down. Stability-wise, Mac OS X is indisputably much more robust than the old Mac OS: a single application, no matter how buggy, can neither bring down the entire system nor bring down other apps.
Microtech’s Crashtacular Zio Driver Thursday, 7 August 2003
