Introduction: software preservation

Software is a class of digital electronic object which is often a prerequisite to the preservation of other electronic objects. However, software has characteristics that make its preservation substantially more challenging than many other types of digital object. Software is inherently complex, dependent on the operating environment, and typically has numerous interacting components. Software preservation is rarely prioritized, and is thus a relatively underexplored topic of research. In this chapter, we consider some of the issues in software preservation. Software can be defined as:

Computer programs are sequences of processor instructions to permit the execution of a specific task. It should be noted that documentation is included, a crucial element in effective software preservation. We refer to a single collection of software artefacts that are brought together for an identifiable broad purpose as a software product.

The term software is sometimes used in a broader context to describe any electronic media content which embodies expressions of ideas stored on film, tapes, records, etc., for recall and replay by some (typically but not always) electronic device. For the purposes of this chapter, such content is considered out of scope.

Software represents a large and diverse domain which includes microcode, real-time control, operating systems, business systems, desktop applications, distributed systems and expert systems, with an equally wide range of applications. We can classify this diversity along a number of different axes, which impact on preservation requirements:

• • Diversity of application. Software is used in almost every area of human activity: business office systems, scientific analysis applications, navigation systems, industrial control systems, electronic commerce, photography, art and music media systems. Each area has different functional characteristics and it is necessary to classify software according to some application-oriented classification or description of the domain.

• • Diversity in hardware architecture. Software runs on a large range of different computer configurations. Assembler and micro-code are used to control the hardware directly, while at a higher level of abstraction applications are deployed on a wide range of computing hardware and architectures. In order to re-create the functionality of a system, the hardware configuration may need to be taken into account.