How Garbage Collector works?

[Borneq]

Użytkownik "Lars T. Kyllingstad" <public at kyllingen.NOSPAMnet> napisał w 
wiadomości news:i40dhi$55q$1 at digitalmars.com...
> Since the GC keeps track of the length of the memory block, it can also
> tell whether the pointer is inside the memory block.
>  if (pointer >= startOfBlock && pointer < startOfBlock + blockLength)
>      doNotCollect();

How compute startOfBlock ? GC keep startOfBlock for each pointer (pointer 
consits of actual pointer and pointer to startOfBlock)?
or search for pointer such Block that pointer betwen 
startOfBlock..startOfBlock + blockLength ?