Originally the Calendar was a program integrated in the Accessories.
Used in Windows 1.0 and 2.0.
Used in Windows 3.0.
Used in Windows 3.1, 95, 98, and ME.
With the release of Windows XP the calendar program stopped being an accessory.
With the release of Windows Vista, the Calendar program became a service linked with Hotmail.
Used in Windows Vista.
Used in Windows 7.
In 2012, Hotmail Calendar was rebranded as Outlook Calendar. This icon was used on Windows 8 & Windows 8.1. This icon continued to be used on Outlook.com until the 2017 redesign.
Used in Windows 10.
Used in Windows 10 and 10X.
A different version of the calendar icon can be seen on the Microsoft Edge Homepage, this icon is used for the online version for Outlook Calendar.
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