Both. I use a 32 bit operating system on a 64 bit computer from 2007. 64 bit operating systems usually run too slow. And I have several applications that work poorly or not at all on 64 bit operating systems. What sense does 64 bit software make? Apache Open Office for example is only offered as 32 bit version and works on every 64 bit computer. Many Linux distributors offer 32 bit versions of their systems e.g. MX-Linux (Debian), Salix (Slackware), Mageia (Mandriva), Puppy Linux. Why do game developers think they have to ignore this?