A significant difference between the Cosmic Cube and most other parallel processors is that this multiple instruction multiple-data machine uses message passing instead of shared variables for communication between concurrent processes.
This computational model is reflected in the hardware structure and operating system, and is also the explicit message passing communication seen by the programmer.
According to Seitz [1985]: The J–Machine was developed by Bill Dally et al. at MIT providing architectural support suitable for Actors.
Each Eval message has the address of an Actor that acts as an environment with the bindings of program identifiers.
The prototype programming language has expressions of the following kinds: An example program for a simple storage cell that can contain any Actor address is as follows: The above program which creates a storage cell makes use of the behavior ReadWrite which is defined as follows: The above behavior is pipelined, i.e., the behavior might still be processing a previous read or write message while it is processing a subsequent read or write message.. For example, the following expression creates a cell x with initial contents 5 and then concurrently writes to it with the values 7 and 9.