The test plans elements execution order is:

• Configuration elements
• Pre-processors
• Timers
• Samplers
• Post-processors
• Assertions
• Listeners

A pre-processor is something that will happen before the sampler executes. To configure the sample request prior to its execution or to update variables that are not extracted from response text pre-processor elements are used.

Some of the pre-processor elements are

• HTTP URL re-writing modifier
• HTTP user parameter modifier
• HTML link parser
• BeanShell PreProcessor

A processor is used to modify the Samplers in their scope.There are 2 Types of processors:

Usually, Test Plan are saved in their XML format, so there is nothing to do with any particular O.S. It can be run on any OS where JMeter can run.

Thread group: For any test plan, JMeter is the beginning part of thread group elements. It is an important element of JMeter, where you can set a number of users and time to load all the users given in the thread group.

Based on the pattern, a regular expression is used to search and manipulate text. JMeter is useful in interpreting forms of regular expression or patterns being used throughout a JMeter test plan.

Variables and functions can be written into any field of any test component.