This is an implementation of the BTree data structure as a Smalltalk collection. It provides log(n) inserts, deletes, and retrieves of values by key. The keys have to be sortable (ie, Magnitudes).
This is useful in situations where you want to minimize the number and size of individual objects that need to be accessed when using a large collection - for example, when objects are being swapped out to an object database such as GOODS. It is probably not a good choice for a collection that will be kept entirely in memory.