I'm a doctor, not a mechanic
Legacy:Renderer
From Unreal Wiki, The Unreal Engine Documentation Site
The renderer used in 3D UnrealEd Viewports is set by the UnrealEd.ini file:
Device=SoftDrv.SoftwareRenderDevice Device=D3DDrv.D3DRenderDevice Device=OpenGLDrv.OpenGLRenderDevice