The Keykos domain models rather well the C++ instance. Keykos refers to the object as implemented by the code that the domain obeys, as contrasted to the C++ object which is embodied by the block of storage referenced by a C++ object referrence. C++ provides no language safety and thus no isulation between objects of the same type or even of different types. Java provides much protection between instances of the same type (class) and provides good protection between objects of different classes. Java and .NET provide no protection from denial of service by programs that abuse space or time resources. Keykos provides such protection.

Protection domain crossings in Keykos are somewhat more expensive than method invocations in C++ or Java and so there will be fewer Keykos objects in a balanced system than in the same system implemented purely in language constructs. A language such as C++ or Java iv very suitable for defining user code for Keykos.