InsideMacintosh, Volume I, page I-10
“Theroutines available for use in Macintosh programs are divided according tofunction, into what are in most cases called “managers” of the feature theysupport. … Most are part of either the Operating System or the User InterfaceToolbox and are in the Macintosh ROM.
“TheOperating System is at the lowest level; it does basic tasks such asinput and putput, memory management, and interrupt handling. The UserInterface Toolbox is a level above the Operating System; it helps youimplement the standard Macintosh user interface in your application. TheToolbox calls the Operating System to do low-level operations. …
“RAM-basedsoftware is available as well. In most cases this software performs specializedoperations (such as floating-point arithmetic) that aren’t integral to the userinterface but may be useful to some applications.” —Inside Macintosh,Volume I, page I-9
“TheMacintosh User Interface Toolbox provides a simple means of constructingapplication programs that conform to the standard Macintosh user interface. Byoffering a common set of routines that every application calls to implement theuser interface, the Toolbox not only ensures familiarity and consistency forthe user but also helps reduce the application’s code size and developmenttime. At the same time, it allows a great deal of flexibility: An applicationcan use its own code instead of a Toolbox call wherever appropriate, and candefine its own types of windows, menus, controls, and desk accessories.
“Figure 2 [below] shows the various parts of the Toolbox in rough order oftheir relative level. There are many interconnections between these parts; thehigher ones often call those at the lower levels.” —Inside Macintosh,Volume I, page I-9
“Tokeep the data of an application separate from its code, making the data easierto modify and easier to share among applications, the [Macintosh UserInterface] Toolbox includes the Resource Manager. The Resource Managerlets you, for example, store menus separetly from your code so that they can beedited or translated without requiring recompilation of the code. It alsoallows you to get standard data, such as the I-beam pointer for inserting text,from a shared system file. When you call other parts of the Toolbox that needaccess to the data, they call the Resource Manager. Although most applicationsnever need to call the Resource Manager directly, an understanding of theconcepts behind it is essential because they’re basic to so many otheroperations.” —Inside Macintosh, Volume I, page I-9
“Graphicsare an important part of every Macintosh application. All graphic operations onthe Macintosh are performed by QuickDraw. To draw something on thescreen, you’ll often call one of the other parts of the [Macintosh UserInterface] Toolbox, but it will in turn call QuickDraw. You’ll also callQuickDraw directly, usually to draw inside a window, or just to set upconstructs like rectangles that you’ll need when making other Toolbox calls.QuickDraw’s underlying concepts, like those of the Resource Manager, areimportant for you to understand.” —Inside Macintosh, Volume I, page I-11