IAAS
Instead of purchasing servers, software, network equipment or data centre storage space, cloud providers can supply IaaS to clients as a fully out-sourced service and be subsequently billed only according to what they have used.
This means the cloud provider owns and maintains the housing, running and maintaining of all the equipment, not the end-user. This also gives the end-user the flexibility to use more or less storage, as required, (called scalability), which is attractive to businesses which might otherwise have needed to have maintained large amounts of storage space even at off-peak times