Google Cloud Messaging (GCM) is a service that helps developers send data from servers to their Android applications on Android devices, or from servers to their Chrome apps and extensions. The Android service was first unveiled on June 27, 2012, at Google I/O 2012 held at the Moscone Center in San Francisco. The Chrome service was announced before Google I/O 2013 as a blog post titled 'Building efficient apps and extensions with push messaging.'
Google Cloud Messaging (GCM) replaces the beta version of Android Cloud to Device Messaging (C2DM). The free service has the ability to send a lightweight message informing the Android application of new data to be fetched from the server. Larger messages can be sent with up to 4 KB of payload data.