What is an instance in SQL Server and why do we need multiple instances on the same computer HD

https://www.udemy.com/t-sql-training/?couponCode=TSQL_10 Hello Friends I have launched a course on T-SQL .Name of the course is T-SQL Training with Real World Scenarios:Tricks of the Trade I believe it has a lot of good contents which will help a lot to a Microsoft SQL Developer . Please check out the following link to check the course contents and if you need this course then the following link also has discounted coupon . https://www.udemy.com/t-sql-training/?couponCode=TSQL_10 What is an instance in SQL Server and why do we need multiple instances on the same machine or computer. In other words what is the advantage of installing multiple sql server instances on the same machine in sql server Also we have discussed what is the difference between default instance and named instance For blog posts , SQL Server and Business Intelligence training ,please visit the website http://www.ellarr.com