Development Hardware no longer available to the copyright holder

This in many ways is like losing the source code. Sometimes a developer only rents or barrows development hardware. Often hardware is sold after use. Sometimes it actually quits working. Whatever the cause, this group of games were made using hardware that became unavailable to the developer later. If the code is to be ported, it must be redone without actually running it to see how it works. Rendered music and graphics also may not be in a format readable by the next choice for a development system. Unrendered data as well, might be in the wrong format.