There is a link on the Main board.
Microcontroller ATSAMD21G18, 48pins LQFP Operating Voltage 3.3V Digital I/O Pins 14, with 12 PWM and UART Analog Input Pins 6, 12-bit ADC channels Analog Output Pins 1, 10-bit DAC DC Current per I/O Pin 7 mA Flash Memory 256 KB SRAM 32 KB EEPROM up to 16KB by emulation Clock Speed 48 MHz
I'm not able to use the BLOG and the FORUM simultaneously on my WIn7/IE11 machine. So, I haven't seen the BLOG comments. (I don't want to go through the whole LogIn/LogOff F12/Clear Stuff.. scenario 4 or 5 times to finally get logged back into the Forums)
Doing some research on the ATSAMD21G18A which is the fully loaded version of SAM D series in the 48pin package. The ATSAMD21J18A has more I/O thanks to it's 64 pin layout, but none of that can be realized in the UNOs footprint. Looks like a decent chip. The D21J18A part could make possible a Mega-Like ArdinoZERO utilizing the 64pin version, but only having a single row I/O header at the back (instead of the MEGA and DUEs dual).
Has the same 1.8v and 3.3v operating characteristics of the ATSAM3X8E.
It will be interesting to learn how the EEPROM emulation works for storing things like calibration data. Looks like you'd write one sketch to configure it using the NVMDriver Config.... Then your development sketch would have the Memory Available.? Too bad the ATSAM3X8E of the DUE can't offer that.
It will also be interesting to see how similar it is to DUE in terms of IDE integration, libraries and coding methodologies. They are both ARM, but the Cortex M0+ is based on ARMv6 (uses Thumb-2 ISA), where as the Cortex M3+ is ARMv7M based (but also uses Thumb-2 ISA).