Null is a special pointer value (or other kind of object reference) used to signify that a pointer intentionally does not point to (or refer to) an object. Such a pointer is called a null pointer.[1] Many implementations use a value of 0 (all bits zero) to represent the null pointer, as this is at the bottom of the address space of most CPUs (although some architectures use a signed address space and use the most negative value). Many operating systems generate an exception when an attempt is made to access this memory address. Some languages use other nomenclature for such a pointer, e.g., Pascal uses nil.