CDN stands for Content Delivery(or Distribution) Network. It is a network of servers usually located in various geographic locations to improve the availability and access speed of a website (or webapp or other media). The main use of CDNs were during the nineteens when inter-continental access was slow, scarce and expensive. Origin server could be in the silicon valley, users from UK would access the node located in UK, so in theory only once the page would be downloaded from the US server to the UK server. Thus allowing the UK visitors to access the page locally resulting in a huge saving in inter-continental bandwidth costs and improved access times for the end users.

Source: http://www.sajalkayan.com/make-your-own-cheap-charlie-cdn.html

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