This paper describes a slightly improved version of Bakers classic two finger collector with generations, as used in all modern GC systems since the mid 80ies. Normally you just use two semi-spaces plus the generation region. This one uses much more generational regions, which was modern in the 80-90ies, but fell out if favor with modern vmm's. Swapping semi-spaces are so much faster. They claim better compaction, which is interesting. Lisp people, like LispWorks should know better, as they tried those things excessively.