The DEC Alpha AXP is the first full 64-bit architecture with full support of an operating system.
Alpha is a general name for an architecture family.
The chips used in implementations vary by implementation. Quote from which is a re-quote from the IBM System 360 architects. Computer architecture is defined as the attributes and behavior of a computer as seen by a machine-language programmer. This definition includes the instruction set, instruction formats, operation codes, addressing modes, and all registers and memory locations that may be directly manipulated by a machine-language programmer. Implementation is defined as the actual hardware structure, logic design, and data-path organization of a particular embodiment of the architecture.