D365 Modern POS (MPOS) Simplified Architecture

Above diagram is showing MPOS simplified architecture with its main components:

MPOS Client 1/2 with Local Hardware Station and Database:
• On left side we can see two MPOS machines are running with local hardware station and database (for offline mode) installed in each machine.
• Actually MPOS supports dedicated and shared hardware station both. Dedicated is recommended due to stability and easy to use but we can use shared hardware station as well. 
• Different peripherals devices are connected with terminals like printer, scanner, MSR etc.
• MPOS has local CRT and Database for offline mode. Once it will not be connected to Online Retail Server then it will work in offline mode through CRT.

MPOS Connected with Server on IIS Cloud/Local:
• On right side we can see that MPOS is connected with server, hosted on IIS (Azure Cloud).
• MPOS can be connected with local IIS in case of RSSU (Retail Store Scale Unit).

Retail Server Hosted Cloud/Local:
• On right side we can see retail server hosted on IIS (Azure Cloud) which is providing data to MPOS. MPOS is calling Retail server for performing CRUD operations on database.
• Retail Server can be hosted on local IIS in case of RSSU (Retail Store Scale Unit).
• Retail Server is comprised of a set of APIs which can be accessed in order to perform operations through POS or online stores.
• It Consists of ODATA API due to which retail server can be connected to any application and supports advance authorization and authentication.
• Retail Server uses CRT for handling data from database. Retail server just holds ODATA request from client and parse it into CRT objects and pass to CRT and then CRT query database.

Commerce Runtime (CRT):
• CRT is part of Retail Server and also hosted with retail server on machine.
• Commerce Runtime is the core engine which performs all the core business operations and contains the business logic for retail.
• It is comprised of multiple layers that are data access layer, workflow layer, service layer and API.

Database (Channel Database / Store Database / Brick and Mortar Database):
• Channel database has multiple names wrote in above heading.
• It will save all data of POS/Online Store or any other client which is calling by Retail Server.
• Channel database will be called from CRT.