What is the full form of ALU

ALU: Arithmetic Logic Unit

ALU stands for Arithmetic Logic Unit. It is a combinational digital circuit which does arithmetic and bitwise operations on integer binary numbers. It is one of the main components of the computer's Central Processing Unit (CPU) that is designed to perform arithmetic and logical tasks.

The ALU results in an integer as it not only performs the calculations concerned with subtraction and addition but also calculates the multiplication of two integers as they are designed to execute integer calculations. Hence, resulting in an integer. Signals are received from the external circuits by the Arithmetic Logic Unit input, and external electronics get outputs signals from ALU as its response.

Signals

An Arithmetic Logic Unit possesses a variety of input and output nets. The nets or signals are nothing other than what are used to convey digital signals between the Arithmetic Logic Unit and external circuitry, i.e. electrical conductors. External circuits add signals to the Arithmetic Logic Unit when an Arithmetic Logic Unit is operating. In response to these signals sent, the Arithmetic Logic Unit then produces and conveys signals via its outputs to the external circuitry.

1. Data: - Three parallel data buses having two input operands and a result output are the components of the basic Arithmetic Logic Unit.
2. Opcode: - The message about an operation selection code is conveyed to the Arithmetic Logic Unit through this parallel bus. The operation selection code specifies the desired operation, arithmetic or logic, in an enumerated value form, which is supposed to be performed by the Arithmetic Logic Unit.
3. Status:
   • Outputs: Supplemental information concerning the result of the current operation of the Arithmetic Logic Unit is part of various individual signals that convey. The general Arithmetic Logic Unit usually contains status signals like overflow, zero, carry out, negative, and more. When an ALU completes each operation, the external registers contain the status output signals. These signals are made available for future ALU operations stored in the external registers.
   • Inputs: Status inputs allow to make any additional information available to the Arithmetic Logic Unit while operating. When the ALU operates, further access to information is permitted by the status inputs to complete the operation successfully.

Circuit Operation

A simple four-bit Arithmetic Logic Unit is the combinational logic circuitry. It is part of the 74181 integrated circuits. An asynchronous change will occur in an Arithmetic Logic Unit as a response to the input changes, as it is a combinational logic circuit. Stable signals are included in the ALU inputs in normal operation.

Functions

Commonly Arithmetic Logic Unit supports numerous bitwise logic and basic arithmetic functions. These operations are typically included in basic general-purpose ALUs

1. Arithmetic operations
2. Bitwise logical operations
3. Bit shift operations

Applications

The application of the Arithmetic Logic Unit is as follows:-

1. Multiple-precision arithmetic
2. Complex operations

History

Mathematician John von Neumann was the one who, in 1945, proposed the concept of the Arithmetic Logic Unit. It was contained in a report produced on the foundations for a new computer called the EDVAC. It was in the early 1970s that microprocessors began to appear. Often insufficient die space for a full-word-width ALU, despite smaller transistors, was present. Examples include the popular Zilog Z80, which has performed the eight-bit additions with a four-bit Arithmetic Logic Unit.

Advantages of ALU

Arithmetic Logic Unit has various advantages, which are as follows:

1. Parallel architecture and applications with high performance are supported.
2. It can combine integer and floating-point variables and get the desired output simultaneously.
3. It can react to a very large set of instructions and has a higher accuracy range.
4. The ALU can combine two arithmetic operations in the same code, like subtraction, addition and multiplication, or any other two operands. For case, A+B*C.
5. They remain uniform throughout the whole program and are spaced so they cannot interrupt parts in between.
6. It is very fast in general and hence provides results very quickly.
7. No sensitivity issues or memory wastage issues are there with ALU.
8. They minimize the logic gate requirements and are less expensive.

Disadvantages of ALU

The disadvantages of the Arithmetic Logic Unit are discussed below:

1. Floating variables have more delays, and all within the ALU do not easily understand the designed controller.
2. If memory space were definite, the bugs would come and interrupt our resulting output.
3. The Amateurs are hard to understand due to their complex circuit, and also, it is hard to understand the concept of pipelining.
4. The presence of irregularities in latencies is a proven disadvantage of ALU.
5. Rounding off is another disadvantage, as it impacts accuracy.