Google has invested more than $21 billion in its Internet infrastructure since the company began building its own custom data centers in 2006. The company's spending has intensified in recent quarters as Google has launched a global expansion of its data center footprint, which has led to quarterly spending in excess of $1 billion. The company invested a record $1.6 billion in its data centers in the second quarter of 2013.

The analysis of Google's spending provides some context for the scale of the infrastructure being used to power the cloud computing platforms powering popular web apps and services. Microsoft recently disclosed that the company has spent more than $15 billion on its data center infrastructure.

While results may fluctuate from quarter to quarter, the need to invest in infrastructure continues apace. The only time the company has spent more on capital expenditures was the fourth quarter of 2010, when it spent $2 billion purchase of 111 8th Avenue, primarily for its office space. Here's a chart of Google's capital spending by quarter:

Google's data center construction will likely continue at high levels in coming quarters, as since November the company has announced a $200 million expansion in Council Bluffs, Iowa, a $600 million expansion at its campus in Berkeley County, South Carolina and another $600 million to expand its campus facilities in Lenoir, North Carolina, and $390 million to add capacity to its facility in Belgium. Google is also expanding its infrastructure in South America and Asia.

A capital expenditure is an investment in a long-term asset, typically physical assets such as buildings or machinery. Google says the majority of its capital investments are for IT infrastructure, including data enters, servers, and networking equipment. In the past the company's CapEx spending has closely tracked its data center construction projects, each of which requires between $200 million and $600 million in investment.