Two SAP application components in RSA5 & RSA6?

Hi All,

Do anyone know why there are TWO SAP-R/3 (SAP application components) in the RSA5 & RSA6(tcode)? Under SAP node, there are two SAP-R/3 and they are all the same. I am wondering if there is a reason for that.

I research here but was not able to find an answer for it. Can someone share with me?

Thank you.