Maurice Herlihy discusses wait-free synchronization in concurrent systems. A wait-free implementation guarantees that any process can complete any operation in a finite number of steps, regardless of other processes' speeds. He introduces a technique to prove that certain data objects cannot be implemented wait-free using others. He shows that atomic read/write registers are at the bottom of a hierarchy of objects, as they cannot be used to construct wait-free implementations of many data types. However, he also shows that there exist universal objects from which any sequential object can be implemented wait-free. These universal objects have a consensus number greater than or equal to the number of processes in the system. The paper presents impossibility results showing that certain data structures, such as queues, stacks, and lists, cannot be implemented wait-free using atomic registers. It also shows that certain synchronization primitives, such as test&set and fetch&add, are computationally weak. The paper concludes that further progress in wait-free synchronization requires focusing on more fundamental primitives rather than traditional read and write operations. It also highlights the limitations of certain multiprocessor architectures and shows that message-passing architectures like hypercubes are not universal. The paper presents several theorems and corollaries that demonstrate the impossibility of implementing certain data structures and synchronization primitives wait-free.Maurice Herlihy discusses wait-free synchronization in concurrent systems. A wait-free implementation guarantees that any process can complete any operation in a finite number of steps, regardless of other processes' speeds. He introduces a technique to prove that certain data objects cannot be implemented wait-free using others. He shows that atomic read/write registers are at the bottom of a hierarchy of objects, as they cannot be used to construct wait-free implementations of many data types. However, he also shows that there exist universal objects from which any sequential object can be implemented wait-free. These universal objects have a consensus number greater than or equal to the number of processes in the system. The paper presents impossibility results showing that certain data structures, such as queues, stacks, and lists, cannot be implemented wait-free using atomic registers. It also shows that certain synchronization primitives, such as test&set and fetch&add, are computationally weak. The paper concludes that further progress in wait-free synchronization requires focusing on more fundamental primitives rather than traditional read and write operations. It also highlights the limitations of certain multiprocessor architectures and shows that message-passing architectures like hypercubes are not universal. The paper presents several theorems and corollaries that demonstrate the impossibility of implementing certain data structures and synchronization primitives wait-free.