Amazon.com's growth engine is in the cloud.

The e-commerce giant said on Thursday that revenue in its Amazon Web Services (AWS) division jumped 47 percent in the fourth quarter to $3.5 billion, more than twice the growth of the company as a whole.

Companies ranging from small Silicon Valley start-ups to units of some of the world's largest banks and makers of industrial products are turning to Amazon's expansive data centers and homegrown infrastructure to run their data centers. Workday and Capital One Financial have recently signed onto the platform.

In addition to providing a big sales boost to Amazon, AWS also ingests tech profits into a company that's traditionally run on very slim margins.

"Cloud computing really has been fueling its earnings growth," said Louis Navellier, chairman of investment firm Navellier & Associates, in an interview on CNBC. "It really helps ensure profitability every quarter now."

Operating income at AWS surged 60 percent to $926 million, accounting for almost three-quarters of total operating profit.

While AWS is growing rapidly, revenue in the unit did slightly miss expectations. Analysts had predicted sales of $3.6 billion, according to FactSet.