Back in 2006, Amazon (AMZN - Get Report) pioneered a radical way for storing data. Instead of companies needing to buy physical hardware to store information on their own premises, they could store their information in the cloud, using Amazon's new Web Services platform.

Fast forward ten years, and that idea has shifted from radical to mass adoption. In a survey 451 Research ran in the fourth quarter of 2015, only 10% of companies said they don't use any form of cloud. The cloud market as a whole accounted for roughly $110 billion in revenues for the 12 months ending last September, according to Synergy Research, and Amazon alone projects its cloud revenues will reach $10 billion this year. 

While Amazon still maintains a significant lead, it is no longer the only player. The major cloud services providers in infrastructure and platform services today are Amazon, Microsoft (MSFT - Get Report) , Google (GOOG - Get Report) (GOOGL - Get Report) , and IBM (IBM - Get Report) , and they're all gunning for enterprise customers to use their cloud platform.

According to a survey from Synergy Research Group, Amazon Web Services had a 31% market share of the cloud market in 2015, followed by Microsoft's Azure with 9%, IBM's Softlayer with 7%, and Google's Cloud Platform with 4%. While AWS grew revenues 63% year-over-year, Azure grew 124%, IBM grew 57%, and Google grew 108%.

As competition increases, it's unclear whether Amazon can maintain that strong lead.

Just last month, Oppenheimer analysts lowered their estimates for AWS based on "increased competitive concerns." The downgrade followed reports that Apple (AAPL - Get Report) was moving some of its data from AWS to Google's Cloud Platform. Spotify also said it was moving some of its cloud business from Amazon to Google in February, while Dropbox announced in March that it was moving most of its customer's data to on-premises storage and out of Amazon's cloud.

"While AWS is still far ahead of the competition in features and services, as reflected in zero price reductions in 2015, we cannot ignore recent press reports of potential client losses (Apple, Spotify and Dropbox)," the analysts said. They noted that as competition increases, a price war will have to be waged, which means lower margins for AWS.

Other analysts have also highlighted the shifting tide.

"Competitive pressures in the infrastructure space have been heating up for the past few months, with Alphabet and Microsoft slowly trying to muscle in on AWS's one million active customers," BTIG analyst Joel Fishbein wrote last month.

In general, it's agreed that cloud platforms are and will continue to be the future of infrastructure and data storage.

"When we ask people why they use cloud, it's a combination of saving money, saving effort and getting out of the business of doing things that don't drive competitive advantage," said Andrew Reichman, research director of cloud at 451 Research. Companies are realizing that spending time, money and energy on the technology infrastructure isn't necessarily a good investment when they could be focusing on their core business.

The question is how each of the Big Four, who together account for more than half of the worldwide cloud market, can differentiate themselves from their competitors to attract customers.

Microsoft and IBM may be newer to the cloud business than Amazon, but they've been dealing in the traditional infrastructure space for much longer. And they may have the upper hand in helping older businesses transition to the cloud since they were already working with them before.

Both IBM and Microsoft are also quick to emphasize their expertise in enabling hybrid solutions, where only a portion of a company's data is in the cloud.

"There's no question that Amazon has done great things for the industry," said IBM's Cloud CTO, Jim Comfort. "[But] we are convinced the solution will be hybrid. It's not just move to the cloud, it's use the cloud to transform your business and connect the investments you have with new investments in a way that makes sense."

Julia White, general manager of cloud platform marketing at Microsoft, noted how its clients have the capability to use Azure as well as on-premises data centers via one consistent experience. White also pointed to Microsoft's wide reach, with a presence in 30 different regions around the world.

"Cloud in general is a place where there's economy at scale," White said."The efficiencies we get --those are economics that we get at massive scale and can pass on to customers. Unless you get that scale, it's hard to have a competitive price offering."

Amazon counters the legacy players with innovation and top-notch technology. But there may be a reluctance on the part of some companies, especially retailers, who may not want to give any business to a competitor like Amazon.

"Our general philosophy is we want to find things -- businesses that customers love, that can grow to be large, will provide strong financial returns, and are durable that can last for decades," Amazon CFO Brian Olsavsky said during the company's January earnings call. "We think AWS is that."

Amazon did not respond to a request for comment for this story.

Google, too, offers innovation, and as the company highlighted at its recent conference, an edge in terms of machine learning, where computers are programmed to learn and figure out things on their own. Plus, Google's pricing is 50% lower than other providers, according to Oppenheimer, since they give high-usage discounts to attract enterprise customers.

But up until now at least, Google seems to be drawing smaller players and struggling to convince a large number of enterprises to jump aboard. The reported Apple win is big, but compared to AWS's huge client base, it's still paltry. 

"I would say [Google has] had limited success so far," said 451's Reichman. "They have neither the deep relationships with enterprises nor the broad technology that Amazon has, so it's unclear exactly what they're going to do."

Alphabet is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells GOOGL? Learn more now.

During the fourth quarter earnings call Google CEO Sundar Pichai said that the company planned to invest more in cloud in 2016, reflected by the recent hire of Diane Greene, the founder of a cloud services company called VMware. And according to a Google spokesperson, Google's core cloud storage business is growing seven times year-over-year, while its cloud computing business is growing five times year-over-year.

Likely recognizing the increasing heat, Amazon has been working on ramping up its cloud roster, reportedly trying to win over big U.S. banks by explaining to them how AWS can more easily handle spikes in demand, as well as looking to take a stake in a digital mapping company in order to get their cloud business (Microsoft is also competing for that company's business).

But for now at least, Amazon and the three other major cloud players need not worry too much. Since there are still so many companies who have yet to move to cloud, there's more than enough demand for each player to sustain its business.

"There's a tremendous amount of growth potential in the cloud," Reichman said. "We're at least five years away from market saturation, where everybody is using a cloud player and when they're going to be fighting with each other to win deals away. There's a ton of runway for each of those companies to win the stuff they're good at without stepping on each others' toes."