Classic mode vs ARM mode

When working with Azure using PowerShell there are 2 different ways you should be aware of and you will see a lot of the Microsoft documentation referring to both of them:

Classic mode (Service Management)

This is the old way of operating Azure and managing Azure. There is still some services in Azure that can only be managed using the classic mode, even though more and more services are moving towards the new ARM mode.
To list modules installed on your machines operating under classic mode you can do the following:

Get-Module -ListAvailable Azure.*

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"Resource manager (ARM) "

This is the new way of managing Azure (Based on the REST API's provided). Most of the services you could manage in Azure from Powershell classic mode can now be managed using the new mode with some exceptions. This should be the preferred way of managing your Azure resources unless you have certain services that are not supported under ARM mode yet.