Editing Dataflow architecture (section)

== History ==
Hardware architectures for dataflow was a major topic in [[computer architecture]] research in the 1970s and early 1980s. [[Jack Dennis]] of [[Massachusetts Institute of Technology|MIT]] pioneered the field of static dataflow architectures while the Manchester Dataflow Machine<ref name="Manchester-Dataflow">[https://web.archive.org/web/20120730230237/http://cnc.cs.manchester.ac.uk/projects/dataflow.html Manchester Dataflow Research Project, Research Reports: Abstracts, September 1997]</ref> and MIT Tagged Token architecture were major projects in dynamic dataflow.

The research, however, never overcame the problems related to:

* Efficiently broadcasting data tokens in a massively parallel system.
* Efficiently dispatching instruction tokens in a massively parallel system.
* Building [[content-addressable memory]] (CAM) large enough to hold all of the dependencies of a real program.
Instructions and their data dependencies proved to be too fine-grained to be effectively distributed in a large network. That is, the time for the instructions and tagged results to travel through a large connection network was longer than the time to do many computations.

[[Maurice Wilkes]] wrote in 1995 that "Data flow stands apart as being the most radical of all approaches to parallelism and the one that has been least successful. ... If any practical machine based on data flow ideas and offering real power ever emerges, it will be very different from what the originators of the concept had in mind."<ref>M. V. Wilkes, ''Computing Perspectives'', Morgan Kaufmann, 1995, ISBN 1-55860-317-4, page 79.</ref>

[[Out-of-order execution]] (OOE) has become the dominant computing paradigm since the 1990s. It is a form of restricted dataflow. This paradigm introduced the idea of an ''execution window''. The ''execution window'' follows the sequential order of the von Neumann architecture, however within the window, instructions are allowed to be completed in data dependency order. This is accomplished in CPUs that dynamically tag the data dependencies of the code in the execution window. The logical complexity of dynamically keeping track of the data dependencies, restricts [[out-of-order execution|''OOE'']] [[CPU]]s to a small number of execution units (2-6) and limits the execution window sizes to the range of 32 to 200 instructions, much smaller than envisioned for full dataflow machines.{{cn|date=July 2023}}