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2. Context and Motivation
Table 2.1.: Flynn’s taxonomy
Data Stream
Single Multiple
Instruction Single SISD SIMD
Stream Multiple MISD MIMD
2.4.1. Taxonomies
To structure the discussion of the vast field of concurrent and parallel programming,
this section reviews two taxonomies proposed in the literature.
These two taxonomies unfortunately do not match the focus of this dissertation.
Therefore, a partial taxonomy is introduced to structure the discussion
here and in later chapters of this dissertation.
Flynn’s Taxonomy
Flynn’s taxonomy can be used as a coarse categorization of programming
concepts [Flynn, 1966]. Originally, the proposed taxonomy is meant to categorize
computer organizations, but it is abstract enough to be used in a more
general context. Flynn based it on the notions of instruction streams and data
streams, where a set of instructions forms a program to consume data in a
given order. Using these notions, Flynn identifies four possible categories (cf.
Tab. 2.1): single instruction stream - single data stream (SISD), single instruction
stream - multiple data streams (SIMD), multiple instruction streams - single data
stream (MISD), and multiple instruction streams - multiples data streams (MIMD).
For the purpose of this dissertation, SISD represents classic single threaded
programs. SIMD corresponds to single threaded programs that use vector
instructions to operate on multiple data items at the same time. MISD can
be understood as a multi-threaded program that runs on a single core with
time shared execution without exhibiting real parallelism. Thus, each thread
of such a program corresponds to a distinct instruction stream (MI), but the
observable sequence of memory accesses is a single data stream coming from
a single data store. MIMD corresponds then to applications with multiple
threads executing in parallel, each having its distinct stream of memory access,
i. e., separate data streams and data stores. Since the concurrent and
parallel programming concepts relevant for this dissertation are variations of
multiple instruction streams (MI), Flynn’s taxonomy is too coarse-grained to
structure the discussion.
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