Describe IUKNOWN interface

All COM object supports atleast one interface, that is  IUnknown interface. All interfaces are the classes, derived from the base class IUnknown. Every interface supports methods access data and perform operations transparently to the programmer. taking example, IUnknown supports 3 methods, AddRef, Release(), & QueryInterface(). Assuming that pinterf is a pointer to an IUnknown. pinterf->AddRef() increments the reference count. pinterf->Release() decrements the reference count, deleting the object when the reference count reaches 0(zero). pinterf->QueryInterface( IDesired,pDesired) checks to watch  if the current interface (IUnknown) supports another interface, IDesired, creates an instance (via a call to CoCreateInstance()) of the object if the reference count is 0 (the object does not yet exist), and then calls pDesired->AddRef() to increment the reference count (where pDesired is a pointer to IDesired) and returns the pointer to the caller.