Azure AD vs On-Premises Active Directory: What's the Difference?

You might have heard your setup described as “on-prem AD,” “Azure AD,” “Entra ID” (Microsoft’s newer name for Azure AD), or “hybrid.” All of these are about the same underlying job: keeping track of who’s allowed to sign in to what. Here’s what the difference actually means for you.

What both of them do

Whichever one your business uses, its job is the same: it’s the system that checks your username and password are correct, decides what you’re allowed to access, and is what makes a single sign-on happen behind the scenes (see What Is Single Sign-On (SSO)?). The difference is where that system lives and what that means practically.

On-premises Active Directory

This is the traditional approach: a server, physically in your office (or in a data centre you control), that holds every user account, computer, and permission. It’s been the standard way of doing this for over 20 years, and plenty of businesses still run it, often alongside newer cloud tools.

What it means for you: signing in to a computer joined to on-premises AD checks in with that local server. On the office network, this is instant and invisible. From outside the office, you’ll usually need to connect to the VPN first — see What Is a VPN? Work VPN vs Personal VPN — because your laptop needs a way to reach that server.

Upsides:

Full local control over the server and exactly how it’s configured.
Keeps working even if your internet connection drops, as long as you’re on the local network.
Some older line-of-business software was built expecting a local server like this, and works best with it in place.

Downsides:

Needs a physical or virtual server that has to be maintained, patched, and backed up.
Signing in remotely means connecting to a VPN first, rather than just opening your laptop.
More hardware and maintenance overhead than a cloud-only setup.

Azure AD / Entra ID

This is Microsoft’s cloud equivalent — the same underlying job (tracking accounts and permissions), but running in Microsoft’s cloud instead of a server in your office. Newer businesses, and businesses built primarily around Microsoft 365, often run entirely on this.

What it means for you: you sign in exactly the same way whether you’re in the office, at home, or travelling — no VPN needed just to sign in, because there’s no on-site server to reach. It’s what powers a lot of the modern conveniences you might already be used to: signing in once for most Microsoft 365 apps, MFA prompts, and (on some setups) extra checks based on your location or device.

Upsides:

No physical server for your business to maintain.
Sign in from anywhere without connecting to a VPN first.
Built-in modern security features (MFA, and conditional checks like blocking sign-in from unexpected locations) come as standard rather than needing to be bolted on.
Scales easily as the business grows — adding a new starter doesn’t need new server capacity.

Downsides:

Relies on having a working internet connection to sign in at all.
Some older, on-site-only software wasn’t built with this in mind and may need extra work (or won’t work at all) without a local server present.
Moving from an existing on-premises setup to cloud-only is a genuine project, not a quick switch.

Hybrid — running both together

Many businesses run a mix of both, syncing accounts between an on-premises server and Azure AD/Entra ID, so the same account works in both worlds. This is common partway through a move from on-premises to cloud, and some businesses run it long-term if they have a genuine mix of older on-site systems and newer cloud apps.

Which one does my business use?

It depends on your setup, and honestly isn’t something you need to know to do your job day to day — but it’s useful context if you’ve ever wondered why signing in works differently in different situations (needing the VPN in one place but not another, for instance). If you’re curious which your business runs, or why something behaves a certain way because of it, ask support.