Passage One

Computing clouds —essentially digital-service factories一are the first truly global utility, accessible from all corners of the planet. They are among the world's biggest energy hogs and thus account for a lot of carbon dioxide emissions. More happily, they allow firms in developing countries to leapfrog traditional information technology (IT) and benefit from advanced computing services without having to build expensive infrastructure.

The clouds allow computing to be removed from metal boxes under desks and in firms⁵ basements to remote data centers. Some of these are huge, with several hundred thousand servers. The “cloud of clouds” has three distinct layers. The outer one, called “software as a service” (SaaS), includes web-based applications such as Gmail, Google's email service, and Salcsforcc.com, which helps firms keep track of their customers. Going one level deeper, there is “platform as a service” （PaaS)， which means an operating system living in the cloud. Such services allow developers to write applications for the web and mobile devices.

The most interesting layer— the only one that really deserves to be called “cloud computing”， say purists— is “infrastructure as a service” （IaaS). IaaS offers basic computing services, from number crunching to data storage, which customers can combine to build highly adaptable computer systems.

This layer is the hardest to measure. It is growing rapidly and firms do not report revenue numbers; nor are they very forthcoming with information, arguing unconvincingly that this would help their competitors. Amazon, for instance, only reveals that it now stores more than 200 billion digital“objects” and has to fulfill nearly 200,000 requests for them per second— impressive numbers but not very useful ones.

This reluctance to share information has inspired analysts and bloggers to find out more, in particular about Amazon. Guy Rosen, a blogger, and Cloudkick, a San Francisco start-up, have come up with a detailed estimate to the size of at least part of Amazon's cloud. Mr. Rosen decrypted the serial numbers of Amazon's “virtual machines”， the unit of measurement for buying computing power from the firm. Alex Folvi, the founder of Cloudkick, then used these serial numbers to calculate the total number of virtual computers plugged in every day. This number is approaching 90,000 for Amazon s data centers on America's East Coast alone.

So how big is the cloud? And how big will it be in, say, ten years? It depends on the definition. If you count web-based applications and online platforms, it is already huge and will become huger. Forrester predicts that it will grow to nearly $56 billion by 2020.

At any rate, the cloud is not simple “water vapor”, as Larry Ellison, the boss of Oracle, a software giant, has deflating suggested. One day the cloud really will be big. Given a little more openness, more people might actually believe that.

What is true of computer clouds, according to the first paragraph?

The most important part of the “clouds” is aimed to provide ________.

The author cites the example of Amazon, in Paragraph 4, to show that________.

What did the blogger Mr. Rosen do according to Paragraph 5?

The author suggests that the prospect of the computer clouds is ________.