Initially, Google used the official date of business operation in 1998 to count birthdays. Most of the day, Google officially opened 7/9 as a birthday, but Google also changed often 'depending on when people want to eat cake'. Perhaps because of the same day of the World Trade Center bombing, they moved.
In recent years, Google's birthday is usually September 27, you will see Google Doodle on that day. If you want to see it as soon as possible, try viewing the Google page in the time zone countries sooner.
Another interesting thing is that if you log in to your Google account, you will see a birthday cake on your birthday.
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