The processor is the heart, the central working element, of a computer or other digital information handling system. It is the part that does all of the processing, the actual work of performing arithmetic and logic operations. Everything else in current computers mostly only holds information, as bits. Some technical names for processors: Central Processing Unit (CPU), Arithmetic Logic Unit (ALU). Processors can be made in many parts or in one part (monolithic). Older processors were always in many parts, current ones are usually monolithic. There is no one necessary model or configuration for processors. The term's meaning varies with context, mainly by how processors are defined or implemented. Historically, the evolution was as: many cabinets in several rooms, then many cabinets in one room, then many boards in one cabinet, then many chip carriers on one board, then some as a few chips in one chip carrier (package). Key trait: all parts are treated, and work, as one processing unit during some task. Processors that fit fully on one integrated circuit chip are usually called microprocessors, and have parts (features) measured in microns or micrometers (millionths of a meter), or in nanometers (billionths of a meter). The future will bring nanoprocessors, with parts measured in a few nanometers, and made with a technology called nanotechnology. On this page, processors are arranged in three groups and levels: 1) Top: issues spanning multiple unrelated processors. 2) Middle: types or classes of processors. 3) Bottom: specific processor families, with their own directory category.