The mainframe and hardware have undergone a long evolution. The evolution has resulted in the well-known attributes of reliability, availability, and scalability. From its 24-bit, single CPU, real storage origins it has developed into architectured, 64-bit, SMP machines with virtualization not only of storage, but also of CPU and I/O resources. A single server is capable of supporting hundreds of operating system images.
The mainframe today is a multipurpose machine, optimized for data processing in a business environment and it continues to evolve in response to new business needs.