Virtual Multi-Processor

The first starting idea: optimizing a multi-processor means to share the expensive, not frequently used resources.

The second starting idea: virtual vs. actual in a multi-processor structure must be based on the cheap, most frequently used resources.

In the late '70s the most costly resources in a general purpose microprogrammed processor were: the ALU and the microprogram memory. In the same time the possibility to provide a big number of registers was increased by the possibility to use cheap MSI TTL chips containing dual port static RAMs.

In order to use efficiently the costly resources and to take the advantages of the cheep resources I proposed, in my PhD thesis [Stefan '79], a processor architecture called Virtual Multi-Processor, with two new features:

pipelined multi-threaded execution allowing to share the costly resources to support many computations (threads)
multiple banks of registers allowing one-cycle context switch

The number of the actual threads executed in parallel was limited to the number of pipeline stage of the processor (in the actual machine a two level pipeline processor was implemented).

The number of virtual machine was limited to the number of memory banks used to implement the register file of the processor (4 in the actual implementation).

The first working prototype was built in 1978 in the Functional Electronics Laboratory (Polytechnic Institute of Bucharest) as the CPU of the graphic machine DIAGRAM.

The Virtual Multi-Processor architecture was used to design and implement the DIALISP system, a LISP Machine [Stefan '84].

For a better understanding of this kind of architecture see [Stefan '96] or click on:
http://www.mips.com/content/PressRoom/PressReleases/2006-02-06.multi
to see a late implementation of the same idea in the context of the current technologies.

References

[Stefan '79] G. Stefan: LSI Circuits for Processors, Ph. D. Thesis in Polytechnical Institute of Bucharest, 1979. (in Romanian)
[Stefan '84] G. Stefan, Aurel Paun, Andy Birnbaum, Virgil Bistriceanu: "DIALISP - A LISP Machine", The 1984 ACM Symposium on LISP and Functional Programming, 1984. p. 123-128.
[Stefan '96] G. Stefan: "A Multi-thread Approach in order to Avoid Pipeline Penalties", in Proceedings of 12th International Conference on Control Systems and Computer Science, Vol. II, May 26-29, 1999, Bucharest, Romania. p. 157-162.