Difference between host agent and diagnostics agent

Hi gurus,

I have a confusion for so many days on use and need for these following components in the context of monitoring / basis Administration .  Appreciate if someone helps

why and when to use following components and what is the difference among them.

1. SAP Host agent

2. SAP disgnostics agent ( DAA ) that gets instaeed as seperate instance during the regular spa installation

2. SAP CCM4X

4. SAP CCMSR

5. Wily diagnostics agent

Regards,

Rajesh.