For the increasing market of smart phones, mobile internet devices, and ultra-mobile PCs, mainstream vendors propose two approaches: one is based on ARM SoC, and the other is based on power-efficient x86 processor. However, either approach has its own limitation. The ARM-based approach lacks application software while the x86-based approach does not support flexible SoC extension. To overcome the limitations, we propose the PKUnity86 SoC architecture, which is based on AMBA bus architecture to support fast IP integration. Furthermore, it contains a reduced AMD Geode GX2 processor and several specific designs to support Microsoft Windows and exploit the massive PC software resources. This paper presents two FPGA prototypes of PKUnity86: P86-Core and P86-Min. For P86-Core, which is to verify the core of PKUnity86, we change the RTL code of the reduced Geode GX2 to make it FPGA-synthesizable and implement it on a Xilinx Virtex-4 LX200 FPGA device. We connect the FPGA board to a Geode SP4GX22 motherboard so that we can do full-system emulation. For P86-Min, which is to verify the minimum set of PKUnity86, we implement the RTL code on two Xilinx Virtex-4 LX200 FPGA devices and emulate the full system on a single FPGA board. In addition, we adopt a hardware-software co-development methodology and employ various debug tools to facilitate building P86-Min. Both prototypes reach its own compatibility goal: P86-Core supports Windows XP and previous versions and P86-Min supports Windows 98 and previous versions. The evaluation results show that PKUnity86 achieves Windows compatibility with small hardware overheads and no performance loss.