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The Viking project to land robot laboratories on Mars saw many developments that influenced spacecraft design throughout the '70s and '80s.
The landers pioneered full redundancy and local processing, and were capable of autonomously guiding themselves to the surface. The processors themselves were dual Honeywell HDC 402 processors, 24-bit discrete logic designs running at around 300KHz and each with 18 Kwords of plated-wire memory.
The system software was developed by aerospace contractor Martin Marietta and included virtualisation and multitasking features.
The original plan was to use a more capable computer that could have its instructions changed remotely, but weight problems caused by other aspects of the spacecraft design forced the selection of the lighter — but only third-choice — Honeywell systems.
However, Martin Marietta had adopted a software-first design policy, in contrast to previous projects where the hardware came first, imposing strict limits to changes. With software-first, the developers ran their software in an emulator — indeed, the final hardware was only delivered a couple of months before launch — and were thus able to adapt more quickly to specification changes and discoveries.
More details on the Viking and related projects can be found here.