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In previous posts on garbage collection, I've given a pretty cursory overview as to how things actually work. In this post, I hope to give a somewhat more specific explanation of two incremental (and potentially concurrent or parallel, but we'll ignore that for now) GC algorithms: Yuasa's snapshot-at-the-beginning incremental mark-sweep collector, and the MC2 algorithm. Yuasa's collector is very widely used, for example in Java 5 when an incremental collector is requested. MC2 is a more recent algorithm designed to reduce the fragmentation that mark-sweep creates, and appears to get great performance, though it isn't used much yet. In their practical implementation, both collectors are generational.