Moving vs. non-moving

A moving collector relocates live objects during collection, either by copying them into a fresh region or by compacting them toward one end of the heap. Moving defeats fragmentation and keeps allocation trivially fast, but every reference to a moved object must be found and rewritten, which requires knowing precisely where every reference is.

A non-moving collector leaves every object at the address where it was allocated, for its whole lifetime. References never need fixing, object addresses can be handed to native code freely, and conservative scanning becomes possible. Fragmentation is the price, managed with free lists.

Conservative references and moving are incompatible: a conservatively found "reference" might really be an integer that happens to look like a heap address, so it cannot be rewritten, so its target may never move.

In OrionGC nothing ever moves, which is also why pinning costs nothing: a pinned object's address is as stable as any other object's. See the Overview.