What's the difference between 'SCRUM OPEN' and 'DEVELOPER OPEN'?

Hi,

I'm new to scrum and wanted to go for PSM I certification. As I was going through scrum.org, I see 'SCRUM OPEN' and 'DEVELOPER OPEN' in open assessments. Wanted to know what is the basic difference among them? And for taking PSM I, which assessment should I go for?

Please suggest any book(s) / site(s) where I can read / take more assessments for getting certified.