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Exchange Server 2016 runs much leaner than previous versions and requires less RAM to operate its various roles....
But Exchange Server 2016 hardware requirements are complicated and still up for debate among users.
Microsoft claims that companies can install Exchange Server 2016 on a 30 GB system partition, but that won't support the OS alone, especially if you plan to update it over the years. In practice, admins should have at least 100 GB for the system partition running an Exchange application. Otherwise the databases will end up on a separate disk.
Exchange Server 2016 also requires 8 GB of RAM for the mailbox role and 4 GB for the Edge Transport role; it must run on Windows Server 2012 or later. Microsoft has some guidance available on sizing CPU. Users are probably looking at a bare minimum of two cores running at least 2 GHz each.
Despite these guidelines, many system administrators will run Exchange on some flavor of unsupported hardware.
Exchange 2016 hardware requirements and design
Much like previous versions of Exchange Server, Microsoft still does not recommend virtualization. In practice, there's no real issue with running Exchange in a virtualized environment where the storage runs on top of Network File System. A rather large number of systems administrators have been doing this for years without issue. However, Microsoft does not certify or support this.
If official support is required, look to the Microsoft Server Virtualization Validation Program. You should also check out Microsoft's Exchange 2016 system requirements page. And check that your hardware or hypervisor vendor will support your environment, so you don't have to rely on Microsoft.
An upgrade from Exchange Server 2010 or 2013 to Exchange 2016 features some architectural changes that reduce the stress on the storage subsystem but come with increased CPU requirements. Improved multithreading support balances this out. Also, thanks to the replacement of the Information Store process with the Managed Store process -- a change introduced in Exchange 2013 -- Exchange 2016 ends up being faster in multi-database scenarios on high-core count servers.
Exchange is no longer an application that will consume the resources of an entire physical server. It can run alongside hundreds of applications on a virtualization cluster. Because of this, Microsoft cut the number of roles that Exchange Server 2016 supports. It no longer breaks all the different functions of Exchange into individual systems -- each with their own redundancies and complexities.
Is cloud or on premises cheaper for Exchange?
Upgrade considerations for Exchange 2016
Why admins should consider an Exchange Server 2016 update