Is it better than the Zynq platform ? Parallella still sells SBC with a dual core arm + fpga for 100$ IIRC

Better for FPGA development. The FPGA on the Arty is slightly larger (28K -> 33K logic cells), and all peripherals, including memory, are connected directly to the FPGA instead of through the ARM SoC.

Also, the I/O headers are omitted from the $99 Parallela board, so it's difficult to program. (No JTAG connector.)

Aight thanks. It felt like not having an actual processor was a drag but I'm not in that field. I guess it means you use a separate computer to program the FPGA and then use it standalone, rather than having the FPGA as a dynamic coprocessor.

does it means that it is possible to done the 1680 cores thing on the Arty board? if can't, what made the Xilinx board more suitable to implement the 1680-cores on it ?

The Xilinx board has a ton of logic slices to run the extra cores. It's like chips having more transistors able to do more stuff. The Arty is too small to hold the full design. Might run slower, too, if on a older, process node than the Xilinx FPGA.

Both of them are Xilinx boards. One of them is just a really, really high end xilinx board, so it basically has enough programmable fabric to hold 1680 cores. The other is cheap and can't hold as many cores.

Now that, seems interesting. Thanks!