Legal music downloads were first compiled by Billboard in 2003, but they did not gain mainstream acceptance in the United States until around February 2005, when digital sales for singles started to be included in the Billboard Hot 100 and other Billboard charts. In the year before, the Hot 100 chart was similar to the Hot 100 Airplay chart, because only minor CD-single sales affected the chart. The inclusion of digital singles has immensely helped many songs chart and peak higher, in some cases in the absence of a radio release.
Single certifications were introduced in February 2005. Songs that sell a certain number of copies are often certified by the RIAA with the permission of the artist and the record company.
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