What are the types of environment variables in QTP

In QTP, there are mainly 2 types of environment variables in QTP.

• Built In -
• User Defined  - 

Built in environment variables are read only. for example

print  environment("LocalHostName") ' print machine name

User defined environment variables can be modified. 

There are 2 types of user defined environment variables in QTP.

• Internal - can be modified. They are defined in test settings.
• External -  read only . They are loaded from external file.