CertiGuide to A+ (A+ 4 Real)  9  Chapter 7: History, Installing and Use of the MacOS       9  You are Booted Up, Now What?

Pre-Emptive Multitasking and Protected Memory 1 Symmetric Multiprocessing

Now let us cover virtual memory, or VM. With Mac OS 9 and its predecessors, virtual memory unfortunately meant slower execution, terrible results with certain multimedia applications, and tons of other system burps and glitches. With Mac OS X, VM is much more efficiently managed, enabling the OS to distribute automatically the exact amount of required memory to applications. In earlier versions of the Mac OS you could control the amount of VM used, but it still always suffered some system lags. With Mac OS X, VM is automatic and cannot be controlled or disabled. In Mac OS X, VM is referred to as Advanced Virtual Memory, or Persistent Virtual Memory, but no matter what the name VM is Mac OS X’s great enabler.

We have both protected memory and pre-emptive multitasking thanks in large part to the UNIX foundations for Mac OS X. The true performance of schedulers and kernels in a UNIX environment has been well studied and documented since the birth of the OS.

Pre-Emptive Multitasking and Protected Memory 1 Symmetric Multiprocessing