Permatechnology refers to permacultural approaches to technology. Permacomputing can be thought of as a subset of permatechnology, which in turn can be thought as the technological aspect of permaculture. The concept of permatechnology can therefore be used as a linking piece that provides a larger context for permacomputing.
Computing is somewhat peculiar when compared to e.g. transportation technology: airplanes are not many orders of magnitude faster or more energy-efficient than sailships, but computers can have this kind of contrast to manual calculation and data processing. Computing therefore constitutes an interesting extremity of the technological possibility space.
Another difference is that practically all production of computers is currently based on somewhat destructive and highly centralized processes, so a lot of rethinking and rebuilding is required for the type of technology in general.
All of these peculiarities give permacomputing somewhat unique challenges compared to most other types of permatechnology.