Breaking with its traditional business model, software giant Microsoft Wednesday introduces a subscription service for the Office productivity suite, a set of programs that is the company's biggest earner after its Windows operating system.

The new plan, named Equipt is aimed at home and student users and will cost about 70 dollars a year. For that price users will get all the components of Office, including Word, Excel, PowerPoint, Publisher, Access, and Outlook, as well as the utility and security program OneCare, and other Microsoft services.

The plan will be available from July 15 from retailer Circuit City and customers will be able to use the included software on up to three PCs. Subscribers will automatically receive upgrades to the products at no additional charge as they are released.

While it's the first time that Microsoft has offered Office on a subscription basis to retail customers the company offers its commercial customers subscription access to software and services under programs such as Open License and Select Plus.

The move is widely seen as an effort to fight back against competing productivity suites like Google Docs and OpenOffice which offer compatibility with Office but are available for free.