On April 2, 2014, at the Build developer conference, Microsoft revealed Cortana, its personal digital assistant for Windows Phone 8.1. Microsoft’s own Windows Experience Blog post, published that day, describes Cortana as a Bing-powered assistant that “gets to know you,” answers spoken questions, conducts natural conversations, and can also take typed input for discreet use. It positioned Cortana directly against Apple’s Siri and Google Now, the assistants already on rival phones.
A distinctive idea in the announcement was the “Notebook.” Inspired by how a human personal assistant keeps track of a boss’s preferences, Cortana’s Notebook stored the user’s interests and habits, and Microsoft emphasized that Cortana would check in before assuming you were interested in something rather than acting on data silently. From the Notebook, Cortana could proactively surface flight details, weather, news, traffic, and people-based reminders, and the information synced with Bing on the web when you signed in. Microsoft framed this as building a relationship the user could trust over time.
Cortana launched first as a U.S. beta, with broader U.S., U.K., and China availability planned for the second half of 2014 and more countries in 2015. The assistant later spread to Windows 10 on the desktop, though Microsoft eventually wound down the consumer version as the assistant market consolidated.
For a business reader, Cortana shows Microsoft’s bid to make voice a primary interface across phone and PC, and its “Notebook” framing was an early attempt to make an always-learning assistant feel transparent and consensual rather than quietly surveillant.