is SCCM a single windows service or multiple service that takes its jobs separately from the SCCM db

Question

After installing SCCM I found six windows service installed namely

1. SMS_EXECUTIVE
2. SMS_NOTIFICATION_SERVER
3. SMS_SITE_BACKUP
4. SMS_SITE_COMPONENT_MANAGER
5. SMS_SITE_SQL_BACKUP
6. SMS_SITE_VSS_WRITER

I really wonder the purpose of those services, which one is the parent service which interacts with SCCM Console ?

does that single service handles all the operations of the SCCM or there any delegation for those work ? if so please shed some light in that direction