Microsoft operates two types of following data centers:

• The first type is the production data center, where Microsoft calculates all workloads of its customers and stores all the data.
• The second type is the edge or delivery site. Those sites connect all Microsoft Cloud services to the internet and Microsoft's customers. Edge sites come in two stages of expansion. The smallest one allows Microsoft public direct peering through the internet. With the second stage of expansion, Microsoft allows customers and providers to establish a private connection to the Microsoft backbone using the Microsoft Azure ExpressRoute service. 

The following diagram shows a schematic of the Microsoft data center structure:

Edge and production sites are connected through the Microsoft backbone. Currently Microsoft owns and operates the second largest and fastest full meshed provider backbone of the world.. Microsoft also owns and operates own see cables such as the MAREA cable from Bilbao (Spain) to Virginia (US). 

This map shows the current Microsoft Azure backbone with the new MAREA cable:

While building its backbone, Microsoft acts differently to the other cloud providers. Microsoft builds its own dark fibre cables or leases dark fibre cables and operates the whole backbone itself. Microsoft runs a fully software-defined network and infrastructure for its backbone, using firewall appliances built for network function virtualization.

If you ever have the chance to see a server rack that connects the Microsoft backbone or represents a Microsoft Edge site, it will probably look like this:

If you want to know more about Microsoft regarding data center equipment and software defined, I highly recommend you consult open source and open compute projects. Microsoft is investing highly in these and is very open in the following projects:

• Microsoft cloud servers:
  • Open cloud server platform: https://www.opencompute.org/projects/server
  • ARM-based cloud server project olympus: https://www.opencompute.org/wiki/Server/ProjectOlympus
• Microsoft network cards for backbone and cloud services: 
  • Smart NIC: https://www.opencompute.org/wiki/Server/Mezz
• Microsoft networking and switch software:
  • Project SONiC: https://azure.microsoft.com/de-de/blog/sonic-the-networking-switch-software-that-powers-the-microsoft-global-cloud/