GSdx is a graphics plugin (GS stands for Graphic Synthesizer, the name of the PS2's GPU). Unlike older plugins that relied on software rendering (using the CPU), GSdx utilizes your PC's Graphics Processing Unit (GPU) via hardware acceleration.

It featured a "Software" mode that used the CPU for maximum accuracy and a "Hardware" mode that used the GPU for maximum speed. The Move to a Pluginless Future

Here is a breakdown of why this plugin matters and how to optimize it for your setup. What is GSdx?

Allows you to upscale internal resolution (e.g., to 4K), making 3D models appear much sharper than on original hardware.