Amazon Web Services (AWS) will become a $10 billion business this year, Amazon CEO Jeff Bezos said in a letter to shareholders this week.

While Amazon as a whole "became the fastest company ever to reach $100 billion in annual sales" in 2015, Amazon Web Services will hit the $10 billion mark "at a pace even faster than Amazon achieved that milestone," Bezos wrote. AWS is used by more than 1 million people from "organizations of every size across nearly every industry," he wrote.

AWS launched in March 2006 with the Simple Storage Service (S3). It expanded with the Elastic Compute Cloud (EC2) a few months later, letting customers rent virtual machines over the Internet. The service allowed developers to obtain computing capacity on demand without having to operate their own servers, and over the years, many startups have built online businesses with Amazon's data centers and services providing the back-end infrastructure. It's not just small companies relying on Amazon, though, as big names like Adobe, Capital One, GE, MLB Advanced Media, Netflix, and Pinterest use the online platform.

Amazon has also been used by scientists to run giant calculations that would normally require a supercomputer.

"Today, AWS offers more than 70 services for compute, storage, databases, analytics, mobile, Internet of Things, and enterprise applications," Bezos wrote. "We also offer 33 Availability Zones across 12 geographic regions worldwide, with another five regions and 11 Availability Zones in Canada, China, India, the US, and the UK to be available in the coming year."

Bezos boasted that Amazon remained committed to its cloud computing division despite early critics who asked, “What does this have to do with selling books?”

Amazon on the whole is famous for operating with razor-thin margins, but AWS is making a good profit. AWS had $7.9 billion in net sales in calendar year 2015 with an operating income of $1.9 billion, according to the company's latest earnings statement. Revenue and profit accelerated toward the end of the year, with $2.4 billion in sales in Q4 and $687 million in operating income. AWS would just need to boost sales to $2.5 billion a quarter to hit $10 billion in 2016.

Company-wide, Amazon reported $107 billion in net sales in 2015 with operating income of $2.2 billion, up from $89 billion and $178 million the previous year.

Amazon Web Services faces strong competition today from the likes of Google and Microsoft, but it's still far ahead of US rivals. Measuring by total compute capacity in use, AWS is 10 times bigger than 14 other infrastructure-as-a-service providers combined, among those included in a Gartner report from May 2015. Those 14 include Microsoft, Google, CenturyLink, VMware, IBM, and Rackspace. The report did not include Alibaba's AliCloud service, which reported having more than 1.4 million customers as of June 2014. The China-based company opened two data centers in the US last year.