The very first Xperia smartphone was announced and released way back in 2008, when Sony was still in a joint venture with Ericsson - thus, the handset was called Sony Ericsson Xperia X1. The X1 ran Windows Mobile Professional 6.1, being a high-end device that competed with smartphones like the HTC Touch Pro, Apple iPhone 3G, BlackBerry Bold, or Nokia's Symbian flagships. Interestingly, the world's first Android smartphone - T-Mobile G1 - was launched one month after the Xperia X1.
The X1 had a 3-inch touchscreen display with 480 x 800 pixels - at the time, this screen offered the highest pixel per inch density of any smartphone: 311 ppi. Another notable feature of the handset was its slide-out QWERTY keyboard. The X1 was actually manufactured by HTC for Sony Ericsson (back in the day, HTC used to manufacture phones sold under various brands other than its own). If you're overwhelmed by nostalgia, feel free to check out our Sony Ericsson Xperia X1 review!
After the Xperia X1, in September 2009, Sony Ericsson announced the Xperia X2, which hit the market in January 2010 running Windows Mobile Professional 6.5. The Xperia X2 kept the same form factor of the X1, obviously including a full QWERTY keyboard, though its screen was slightly larger, measuring 3.2 inches (and yet the pixel resolution remained unchanged at 480 x 800). The X2 wasn't received as well as its predecessor, being the last Windows-based Xperia. For a closer look at the device, check out our Xperia X2 review.
The following Xperia model was the Sony Ericsson Xperia X10 - a 4-inch handset that hit the market in March 2010 with Android 1.6 Donut on board. And, yes, this was the first Android-based Xperia. After that, the floodgates of Android handsets opened, and Sony Ericsson (later just Sony) released devices like the Xperia X10 mini, Xperia Arc, Xperia S, and the Xperia Z series.
Earlier this month, Sony announced the Xperia XA, Xperia X, and Xperia X Performance, all part of a brand new X series running Android Marshmallow and replacing the Z series. In a way - since the company launched plenty of other Xperia X handsets years ago - the new Xperia X family represents both a new beginning, and a back-to-the-roots move for Sony (with the major difference that, this time, there's no trace of Windows around).