Via Java-Channel, 1.4.1 Garbage Collection Algorithms:
The 1.4.1 SDK was released with at least six different garbage collection algorithms. To understand the differences between these algorithms, you first need to understand that in 1.4.1 (and previous JVMs since one of the 1.2 releases) the JVM heap is divided into two main areas: the young generation and the old generation.
This article definately raised more questions than it answered for me, but was informative.