In many real systems, size of memory and objects are not known and can not be determined statically and is mainly dependent on data set during run time. For example, a compiler for a programming language will maintain symbol tables and type information which is dynamically constructed by reading the source program where source program can be of any size. In fact, there are very few large programs (or none), not having dynamic memory allocation. Dynamically created data structures like trees, linked lists and hash tables (which can be implemented as arrays of linked lists) are key to the construction of many large software systems.