IaaS – Infrastructure as a Service is short for migrating the back end of your “delivery” system to the cloud. You rent virtual servers and key parts of the cloud network and then have your employees accomplish the data entry INTO the cloud and extract processed results FROM the cloud.
PaaS – Platform as a Service is short for migrating your “applications development” system to the cloud. Your company (or contractor/developer resources – on or off-shore ) use traditional software systems like ERP – Enterprise Requirements Planning, CRM – Customer Relationship Management, and use standard APIs – applications programming interfaces to manipulate the code on a standard, shared platform. The decentralization of the process makes communication more critical, but also accelerates projects by adding a 24 x 7 capability. It also eliminates the need to provide temporary or permanent work space for the development team. They become a virtual workforce.
See Infinitely Virtual for a more thorough description of Iaas and Paas.
Managed cloud services reduce day-to-day enterprise support and change requirements from support to monitoring. But all this comes after deliberate planning, testing, migration and then IT staff retraining for new roles and responsibilities.
Thanks to Marcus Eber and IBM via emarcus.net