The Macintosh Toolbox was a set of resources, drivers, routines and APIs stored in the ROM of "Old World ROM" Macintosh computers. When the original Macintosh was designed, ROM was faster than RAM, and RAM was expensive, so a large part (though not all) of the Macintosh's operating system was implemented in ROM, so that common routines (such as libraries, graphics routines, etc) did not need to be loaded from an operating system file at all. The part of the operating system loaded from disk was named the Macintosh System Software (which many years later was renamed "Mac OS", and is now referred to as "Classic Mac OS".)