This document discusses the arithmetic logic unit (ALU) and its functions. It notes that the ALU performs integer arithmetic and logical operations on two numbers. It takes data from registers inside the CPU and processes it at high speeds, providing immediate results. The ALU acts as the computer's calculator by executing arithmetic operations like addition, subtraction, multiplication and division as well as logical operations like AND, OR, and NOT. It describes how addition is performed step-by-step and provides examples of other logical operations. The document concludes by showing a functional block diagram of the ALU and describing how the control unit controls its operations.

1. R.D.SIVAKUMAR, M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science &
Assistant Professor and Head, Department of M.Com.(CA),
Ayya Nadar Janaki Ammal College,
Sivakasi – 626 124.
Mobile: 099440-42243
e-mail : sivamsccsit@gmail.com
website: www.rdsivakumar.blogspot.in
ARITHMETIC AND LOGICAL UNIT.

2. ARITHMETIC AND LOGICAL UNIT.
It is a digital circuit performs
Integer arithmetic and logical
Arithmetic.
It is capable of two numbers.
The ALU takes data from the
Temporary storage area inside
The CPU called registers.
It processing high speed
memories And immediate result.
The ALU is the computers calculator.
It executes the Arithmetic and logical operations.
The operations include addition, subtraction, multiplication and division.
The logical operation compares numbers, letters and special characters.
The ALU also performs functions such as AND, OR, NoT.

3. ARITHMETIC OPERATIONS.
It is a digital circuit performs
Integer arithmetic and logical
Arithmetic.
It is capable of two numbers.
The ALU takes data from the
Temporary storage area inside
The CPU called registers.
It processing high speed
memories And immediate result.
The arithmetic operation in adding two numbers can be demonstrated through following steps :
Step 1 : The numbers (5 and 8) to be added up are put into two separate memory locations.
Step 2 : The control unit fetches the two numbers from their memory locations into the data registers.
Step 3 : The arithmetic unit looking at the operator (+) uses the accumulator and adds the two numbers.
Step 4 : The ALU stores the result (13) in memory buffer register.
Step 5 : Then the control unit stores the result into a user desired memory location, say ‘sum’.

4. LOGICAL OPERATIONS.
It is a digital circuit performs
Integer arithmetic and logical
Arithmetic.
It is capable of two numbers.
The ALU takes data from the
Temporary storage area inside
The CPU called registers.
It processing high speed
memories And immediate result.
The importance of the logic unit is to make logical operations. These operations
include logically comparing two data items and take different actions based on the
results of the comparison.
FUNCTIONAL DESCRIPTION.
Some of the basic functions performed by the ALU are - add, subtract, logical AND,
logical OR, shift left and shift right on two’s complement binary numbers. The inputs to
be calculated are stored in the input register (AREG) and the input / output register
(ACCUM) for add, AND and OR functions. The shift left and shift right functions
operate on the value in the ACCUM

5. It is a digital circuit performs
Integer arithmetic and logical
Arithmetic.
It is capable of two numbers.
The ALU takes data from the
Temporary storage area inside
The CPU called registers.
It processing high speed
memories And immediate result.
FUNCTIONAL DESCRIPTION.
The above figure illustrates the functional level block diagram of the ALU.
The control unit controls the operations of the ALU by giving appropriate
control signals to select a specific function and then enable the operation after
the data are fed into the registers. The enable bit is made 1 after the data to be
operated are transferred from main memory.

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