The RK3188 was the first product in the RK31xx series, announced for production in the 2nd quarter of 2013. The RK3188 features a quad-core ARM Cortex-A9 clocked up to 1.6 GHz frequency. It is targeted at tablets and Android TV dongles and boxes, and has been a popular choice for both tablets and other devices requiring good performance.
28 nm HKMG process at GlobalFoundries
Quad-core ARM Cortex-A9, up to 1.6 GHz
512 KB L2 cache
Mali-400 MP4 GPU, up to 600 MHz (typically 533 MHz) supporting OpenGL ES 1.1/2.0, Open G 1.1
High performance dedicated 2D processor
DDR3, DDR3L, LPDDR2 support
Dual-panel display up to 2048x1536 resolution
The RK3188T (PX3) is a lower-clocked version of the RK3188, with the CPU cores running at a maximum speed of 1.4 GHz instead of 1.6 GHz. The Mali-400MP4 GPU is also clocked at a lower speed. As of early 2014, many devices advertised as using a RK3188 with a maximum clock speed of 1.6 GHz actually have a RK3188T with clock speed limited to 1.4 GHz. Operating system ROMs specifically made for the RK3188 may not work correctly with a RK3188T.
I forgot to mention that the PX3 is a 3188T.