A study of user-microprogrammable computers

A microprogram notation resembling statements of higher-level languages / Eine Miikroprogrammschreibweise in Anlehnung an Anweisungen höherer Programmiersprachen

“…Probably best known among users and also well documented in the literature [4] (see also [2], [3], and [5]) is IBM's approach to microprogramming support in all but the smallest models of System!360.…”

“…The microinstruction formats differ only in size and not in their basic structure, e.g., with respect to sequencing. [2], [4], because all functionally separable units within a processor structure are controlled by individual microinstruction fields. Thus, already in an IBM System 360 Model 30. essentially a single-byte processor, seven fields are involved in ALU control [7], In view of this situation, the CAS supported family of flowchart microprogramming languages exhibits a high degree of abstraction by showing all possible sequencing paths and providing for largely algebraic substatements.…”

“…The> are also involved in triggering main memory operations. With little over-simplification, this microinstruction word format may even be regarded as some kind of »//'«/'-instruction [2]. At such a level between microinstructions and regular machine instructions, a mnemonic notation of the discussed type has its definite assets for the development as well as maintenance applications.…”

“…Major complaints focus at a lack of flexibility [9], in particular, with regard to the debugging process, scarce documentation [4], and the requirement of utmost familiarity with the processor to be microprogrammed [2], [8].…”

“…With the ever increasing interest in microprogrammingspecifically, among users of data processing equipment -a demand for higher-level language representations of microprograms is being heard of more frequently [2]. Such requests appear only natural despite still valid objections [3], *) An abridged version of this paper [1] In the past, most manufacturers of larger than minicomputer systems considered microprogramming almost as much a design and development activity as creating the logic diagrams.…”