A Central Processing Unit (CPU) has two parts: The Control Unit (CU) and the Arithmetic Logic Unit (ALU). The ALU is a digital circuit that is able to calculate any process that has a mathematical operation such as addition and subtraction, for example, and logic operations between two numbers, and as such is an intrinsic building block of the CPU.
There are multitudes of electronic circuits that have some type of arithmetic operation in order to function, and each will have an appropriate ALU. An example of this is a digital watch that has an ALU to keep adding another second, minute and hour. Modern microprocessors are complex units and so the ALU corresponds to that in its own complexity; in fact, there may be multiple cores, each with multiple execution units and each with multiple ALUs.
A CU is the part of the CPU that is responsible for directing operations. The outputs of the CU control all activity, and can be considered to be a finite state machine. It controls the flow of information through a processor, and is responsible for co-coordinating the activities of other units within it.
What functions as the CU controls depends on the internal structure of the CPU because this is what it controls. Regular processors that can execute x86 instructions will have a CU that will fetch, decode, manage execution and store results. A processor that has a RISC core will need a CU that can do much more: It will manage the translation of x86 instructions to RISC micro-instructions, manage the scheduling of the micro-instructions, and balance the output to ensure that they go where they are supposed to. This type of CU may be broken down into other units so that the tasks that are performed are more manageable.
There are multitudes of electronic circuits that have some type of arithmetic operation in order to function, and each will have an appropriate ALU. An example of this is a digital watch that has an ALU to keep adding another second, minute and hour. Modern microprocessors are complex units and so the ALU corresponds to that in its own complexity; in fact, there may be multiple cores, each with multiple execution units and each with multiple ALUs.
A CU is the part of the CPU that is responsible for directing operations. The outputs of the CU control all activity, and can be considered to be a finite state machine. It controls the flow of information through a processor, and is responsible for co-coordinating the activities of other units within it.
What functions as the CU controls depends on the internal structure of the CPU because this is what it controls. Regular processors that can execute x86 instructions will have a CU that will fetch, decode, manage execution and store results. A processor that has a RISC core will need a CU that can do much more: It will manage the translation of x86 instructions to RISC micro-instructions, manage the scheduling of the micro-instructions, and balance the output to ensure that they go where they are supposed to. This type of CU may be broken down into other units so that the tasks that are performed are more manageable.
