On-Premises Data Center
Historically, all organizations used on-premises data centers. An on-prem data center simply means that the organization maintains all of the IT infrastructure needed by the business on-site.
An on-prem data center includes everything from the servers that support web and email to the networking hardware connecting them to support infrastructure equipment like uninterruptible power supplies (UPS). Depending on the organization, this can range from a server closet to a massive, dedicated private data center like those operated by large tech corporations.
Cloud Data Center
Over time, organizations have increasingly moved away from the on-premises data center. Instead, they have adopted cloud data centers.
A cloud data center moves a traditional on-prem data center off-site. Instead of personally managing their own infrastructure, an organization leases infrastructure managed by a third-party partner and accesses data center resources over the Internet. Under this model, the cloud service provider is responsible for maintenance, updates, and meeting service level agreements (SLAs) for the parts of the infrastructure stack under their direct control.
Shared Responsibility Model
The migration from an on-premises data center to a cloud data center doesn’t mean moving everything to the cloud. Many companies have hybrid cloud data centers which have a mix of on-premises data center components and virtual data centers components. In the figure below we see how as-a-service models are shifting ownership of data center and infrastructure components from a fully owned and operated on-premises facility towards a commodity service model.