Theprocessor is the part of the computer that actually does thecomputations. This is sometimes called an MPU (for main processor unit)or CPU (for central processing unit or central processor unit).
Aprocessor typically contains an arithmetic/logic unit (ALU), controlunit (including processor flags, flag register, or status register), internalbuses, and sometimes special function units (the most common special functionunit being a floating point unit for floating point arithmetic).
Somecomputers have more than one processor. This is called multi-processing.
Themajor kinds of digital processors are: CISC, RISC, DSP, and hybrid.
CISCstands for Complex Instruction Set Computer. Mainframe computers andminicomputers were CISC processors, with manufacturers competing to offer themost useful instruction sets. Many of the first two generations ofmicroprocessors were also CISC.
RISCstands for Reduced Instruction Set Computer. RISC came about as a result ofacademic research that showed that a small well designed instruction setrunning compiled programs at high speed could perform more computing work thana CISC running the same programs (although very expensive hand optimizedassembly language favored CISC).
DSPstands for Digital Signal Processing. DSP is used primarily in dedicateddevices, such as MODEMs, digital cameras, graphics cards, and other specialtydevices.
Hybridprocessors combine elements of two or three of the major classes of processors.