RTX2010

The RTX2010 manufactured by Intersil is a radiation hardened stack machine microprocessor which has been used in numerous spacecraft.
Characteristics.
It is a two-stack machine, each stack 256 words deep, that supports direct execution of Forth. Subroutine calls and returns only take one processor cycle and it also has a very low and consistent interrupt latency of only four processor cycles, which lends it well to realtime applications.
History.
In 1983, Chuck Moore implemented a processor for his programming language Forth as a gate array. As Forth can be considered a dual stack virtual machine, he made the processor, Novix N4000, as a dual-stack machine. In 1988, an improved processor was sold to Harris Semiconductor, who marketed it for space applications as the RTX2000.