An arithmetic and logic unit (ALU) is contained within a central processor unit (CPU). The ALU is a dedicated collection of high speed circuits that performs the arithmetic and logical operations of a computer. The ALU can be physically located adjacent to, or underneath, the processor register. The ALU can be formed in the shape of a square grid.

The arithmetic and logic unit works in concert with a control unit, internal memory, and registers. All together, these functions comprise the CPU. Where the ALU performs mathematical computation, logic decisions and processing of data taken from the registers, the control unit itself will read program instructions, farm out tasks of processing to the ALU, and ensure that the proper sequence is followed according to program instructions.

Error conditions of arithmetic overflow and arithmetic underflow may occur in which the expected portions of numeric words may exceed the space provided for word length or may not be within a range to be represented and processed. Such errors may not affect precision of mathematical computations, but it is possible nevertheless. Such error conditions may be exploitable by criminal hackers (crackers) wishing to remotely install viruses, spyware, or other types of malicious software on a computer.

Because the ALU is where calculations and comparisons occur, this function can be vulnerable to error conditions if error-handling routines are not provided for the CPU as part of the overall computer operating system. Such routines and programs are normally provided as critical and security updates to operating system software and utility software by the original software publisher. The goal is to head off exploitation by crackers of personal and business computers.

The ALU is now contained on the same chip as other necessary computing and processing components thanks to advances in miniaturization. Input/output chips (I/O), integrated circuits (ICs), random access memory (RAM), and even read only memory (ROM) now aid a microprocessor in the same physical component to smoothly perform computing functions.

While the ALU is more known for its ability to provide mathematical and logical processing, a lesser-known subset of these capabilities is found in its processing of text and character strings. An example of this capability is the event when word searches are performed through text: a word fragment is used as the search criteria and the possible matches are then compared and computed by the ALU. A "hit counter" computes the number of successful searches and other memory areas are brought into play as the successful searches are tabulated and presented to the computer operator.

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