Certainly the hardware itself— its design, capabilities, reliability, and price— is important to the success of a new microcomputer, as described in the classic work on the subject. The timely availability of application software (both general-purpose, such as word processors and electronic spreadsheets, and special-purpose, such as statistical packages and equation formatters) is an equally important factor. System software and some general-purpose application software are typically supplied by the manufacturer of the microcomputer, whereas both general-purpose and specialized application software are often provided by “third parties”— individuals and companies with no formal ties to the manufacturer. The volume and quality of this third-party application software can play a major role in the success of a new microcomputer.

If a machine is similar to previous designs, much software can be “ported” directly to it with only minor modifications. On the other hand, if the capabilities of a new machine are no greater than those of established designs, purchasers may have little reason to consider selecting it. Adding innovative hardware capabilities serves to differentiate a new design in the marketplace, but at the same time requires the development of new software to capitalize on unique features. The more diverse the hardware capabilities of a microcomputer, the more complex the software to take advantage of these features is likely to be. In the case of the Macintosh, substantial innovative capabilities for a relatively inexpensive microcomputer were incorporated in the original design (particularly in the areas of screen graphics and user interaction), but the initial 128K RAM made it difficult or impossible to transport those few existing software packages which already incorporated such capabilities (SmallTalk and software packages for the Apple Lisa) directly to the new microcomputer. Thus most software had to be developed from scratch, or, at a minimum, to be extensively modified. The graphics capabilities of the Macintosh were provided primarily through an extensive, proprietary library of assembly-language ROM routines (the QuickDraw library). Other hardware capabilities, such as support for a “mouse” or pointing device, were provided through similar libraries. To use the hardware capabilities efficiently, programs had only to call routines from these libraries. On the one hand, the libraries had the potential for reducing effort for programmers, since the proprietary routines (in some cases highly sophisticated) had already been developed and refined. On the other hand, the sheer volume of the ROM libraries and their documentation meant considerable learning on the part of programmers. This software was unusually complex by the standards of previous microcomputers.