System services are automatically installed when the AOS is installed and are available when the AOS instance is running. They are written by Microsoft in managed code and hence they cannot be customized.
As mentioned, there are four system services as follows:
We will have a detailed discussion of these services later in the chapter. We will not be able to go into every detail of all service operations, but it will be more than enough to get you started. Fortunately, for those who want to dig deeper, these services are well documented on MSDN. For OData in particular, there is a complete documentation available at http://www.odata.org.