The schema is a blueprint of all the objects in a domain. When you create a new forest, a default schema contains definitions for users, computers, and domains. Because you canít have multiple definitions of an object, you can have only one schema per domain.
The file schema.ini contains the default schemaís definition, as well as the initial structure for the file ntds.dit (which stores directory data). The %systemroot%\ntds directory contains the file schema.ini. The file is in plain ASCII format so that you can type it.