An 8-bit processor manipulates with 8 bits simultaneously. For an 8-bit CPU, it will take four operations, a separate operation for addition of each of the four digits. A 16-bit processor will be able to work on two digits simultaneously, so it will need only two operations. A 32-bit processor will complete addition in one operation. The maximum possible word size at the time of writing of these notes is 64 bits.
Most supercomputers have such powerful processors.
What is amazing that modern technology allows to produce 64-bit processors for personal computers and Pentium Pro would be one of the examples. The 32-bit processors are installed in many personal computers, minicomputers, and in most mainframes. Other microprocessors are compatible with them. For example, AMD -K5 is compatible with Pentium. Modern CPUs are downwardly compatible with earlier CPUs of the same series which means that they can run programs designed for earlier CPUs.