Hardware as a Service (Haas), in a grid computing context, is a pay-as-you-go model for accessing a provider's infrastructure and CPU power. Grid computing is a technology in which several computers work together to act as a single, more powerful computer. Some companies sell use of their grids over the Internet on a per-use basis. The user sends data and a program to process that data; the vendor's grid does the processing and returns the result.
Nicholas Carr, author of "Does IT Matter?," first used the term "Hardware as a Service" to describe services such as Amazon.com's Elastic Compute Cloud (EC2).