Functional vs Non Functional Requirements

Requirements are generally split into two types: Functional and Non-functional requirements. 

Functional Requirements: These are the requirements that the end user specifically demands as basic facilities that the system should offer. 

Non-functional requirements: These are basically the quality constraints that the system must satisfy according to the project contract.They are also called non-behavioral requirements.

Functional Requirements	Non Functional Requirements
A functional requirement defines a system or its component.	A non-functional requirement defines the quality attribute of a software system.
It specifies  “What should the software system do?”	It places constraints on “How should the software system fulfill the functional requirements?
Functional requirement is specified by User.	Non-functional requirement is specified by technical peoples e.g. Architect, Technical leaders and software developers.
It is mandatory.	It is not mandatory.
Example 1) Authentication of user whenever he/she logs into the system. 2) System shutdown in case of a cyber attack. 3) A Verification email is sent to user whenever he/she registers for the first time on some software system.	Example 1) Emails should be sent with a latency of no greater than 12 hours from such an activity. 2) The processing of each request should be done within 10 seconds 3) The site should load in 3 seconds when the number of simultaneous users are > 10000