Editing ICL VME (section)

==Development process==
VME was originally written almost entirely in [[S3 (programming language)|S3]], a specially-designed [[system programming language]] based on [[Algol 68R]] (however, VME/K was written primarily in the SFL assembly language). Although a [[high-level programming language|high-level language]] is used, the operating system is not designed to be independent of the underlying hardware architecture: on the contrary, the software and hardware architecture are closely integrated.

From the early 1990s onwards, some entirely new VME subsystems were written partly or wholly in the [[C (programming language)|C programming language]].

From its earliest days, VME was developed with the aid of a [[software engineering]] [[software repository|repository system]] known as [[CADES]], originally designed and managed by David Pearson (computer scientist) and built for the purpose using an underlying [[IDMS]] database. [[CADES]] is not merely a [[revision control|version control system]] for code modules: it manages all aspects of the software lifecycle from requirements capture, design methodology and specification through to field maintenance. 
[[CADES]] was used in VME module development to hold separate definitions of data structures (Modes), constants (Literals), procedural interfaces and the core algorithms. Multiple versions ('Lives') of each of these components could exist. The algorithms were written in System Development Language (SDL), which was then converted to [[S3 (programming language)|S3]] source<ref>{{cite web|url=http://www.doc.ic.ac.uk/~mml/feast2/papers/pdf/jfr95c.pdf|title=Continuing Effort Estimation for Evolution a Case Study|author=Juan F Ramil}}</ref> by a pre-processor. Multiple versions of the same modules could be generated.