This means that there are now two types of garbage collections, minor and major ones.
Minor collections occur relatively frequently but are very fast.
The net effect should be to reduce garbage collection pauses significantly. In addition, the system is more aggressive about allocating more space when a substantial fraction of the allocated space is in use. This should also reduce the number of collections, but may lead to greater process memory growth. The impact on limited memory systems such as a Macintosh with a small partition is not clear at this point. The new garbage collector requires more storage space per Lisp node.