If you have an old app that is preventing your jurney to Microsoft Azure then you can transfer your old machine that runs this application directly on Azure. Virtualization allows to run Old Applications, that need Operating Systems that are not officialy supported on Azure.
You can find out excactly the VM sizes that supports Virtualization at the official documentation: Microsoft Azure offers virtualization layer access at the following series Virtual Machines: The former is usually limited to servers, with the latter finding common use on desktop computers.
Either the multiple operating systems run side-by-side, with a separate piece of software called a hypervisor used to manage them, or one operating system runs the other operating systems within program windows. As a sence, Virtualization, refers to running two or more operating systems one one physical PC. Virtualization has great interest and value to the information systems ecosystem. You can find more info at my post serries about Nested Virtualization here:
For the official nested virtualization support in Microsoft Azure please use the Nested Virtualization feature. This article is about testing VirtualBox on Azure VM, the open-ource virtualization platform of Oracle. VirtualBox on Azure VM for testing or run Old apps