Lightroom / Adobe Camera Raw (ACR) are processing applications that will render raw data from files produced from Digital Cameras they will utilise their own proprietary default settings and profiles to process the raw data which is different to the processing engine utilised by the camera manufacturer, or other raw processing software.LR / ACR utilise a variant of Prophoto RGB as the colour working space. When you render the file to a image file tiff, jpeg etc you can assign a color space of your choice.
I am not aware what "PCS" is, or what role it plays if any.