Managed IT services are based on the concept of which one of the following?

Utility computing is a service-delivery model in which computing resources — processing power, storage, and network bandwidth — are supplied to consumers on demand and billed on a metered, pay-per-use basis, the same way public utilities such as electricity, water, or gas are supplied and billed only for what is actually consumed.

Managed IT services — where a third-party provider (an MSP) takes over monitoring, maintenance, security, and support of a customer's IT environment for a recurring or usage-based fee — mirror this exact relationship: the customer consumes IT capability as a service rather than owning and operating the underlying infrastructure, and is billed according to usage or subscription rather than upfront capital purchase. That is why managed IT services (and, more broadly, cloud computing) are described as being based on the concept of Utility Computing.

Contrast with the other options:

• Virtualization — a technology for creating virtual instances of hardware (virtual machines, virtual storage); it describes how a provider builds infrastructure internally, not the customer billing/consumption relationship.

• Grid Computing — pools many independently owned computers to jointly execute one large computational task; a collaborative distributed-processing model, not a service-consumption model.

• SOA — a software design style that assembles an application from independent, reusable, network-callable services; it concerns software structure, not service delivery or billing.

Hence, the concept managed IT services are based on is Utility Computing.