Abstract: A system includes a processor for executing a collector program to perform a method (e.g., a method of collection). The method includes using an object model during a collection phase that is different than an object model used during program execution. The processor may also perform a method including assigning a hash code to at least some objects, and consulting a structure that maintains a mapping of objects to hashcode values to determine said hashcode for one of said objects. The processor may also perform a method including storing a class pointer and garbage collector state information in a single word, and accessing said class pointer by masking out non-class bits.