@lister-of-smeg said in Stems into two questions about PS1 games...?:

quick howto
https://scunster.co.uk/?p=1732

This quick 'howto' seems like some spam site with information scraped from the real post - which may have originated in the Launchbox forums.
Local info - https://retropie.org.uk/docs/CHD-files/
reddit topic - https://www.reddit.com/r/RetroPie/comments/72kh6q/stepbystep_guide_how_to_convert_sega_cd_or_pc/