Is JMicronATA.kext part of Yosemite? And others There is a file JMicronATA.kext in my GF's iMac in /System/Library/Extensions ... is this an official part of OS X? Or can it be deleted? I ask because its modification date is 2012 and in System Report it shows that it's Not Signed and not loaded. 

As well there are these kexts in /Library/Extensions which do not show to be from Apple, are not loaded, and many are from 2013:

ACS6x.kext
AcrMSR.kext
ATTOCelerityFC8.kext
ATTOExpressSASHBA2.kext
ATTOExpressSASRAID2.kext
CalDigitHDProDrv.kext
HighPointIOP.kext
HighPointRR.kext
PromiseSTEX.kext
SoftRAID.kext

What are all these and why are they in /Library/Extensions instead of /System/Library/Extensions if they are officially part of OS X Yosemite? If they're not, how can I identify where they came from? Why would they still be there after I just reinstalled Yosemite yesterday?

How can you tell what's an official part of the system, and what isn't? How can you uninstall 3rd party crap, short of rooting out individual files from within alllll of the folders in the three different Library folders, not to mention anything hidden in the /private directory??

Thanks.
It's the kernel extension for JMicron SATA controllers, and yes it's official, as are the others. It's up to you if you want to delete them, I wouldn't bother as they take up minimal space. Check System Profiler before doing anything silly just to make sure your iMac doesn't require any of the listed extensions.

Example:


  JMicronATA:
  
  Version:    1.1.6
  
  Last Modified:  5/22/12, 8:19 AM
  
  Loaded: No
  
  Get Info String:    1.1.6, Copyright JMicron Technology Corporation
  
  Obtained from:  Not Signed
  
  Kind:   Intel
  
  Architectures:  x86_64
  
  64-Bit (Intel): Yes
  
  Location:   /System/Library/Extensions/JMicronATA.kext
  
  Kext Version:   1.1.6
  
  Valid:  Yes
  
  Authentic:  Yes
  
  Dependencies:   Satisfied
  
  Signed by:  Not Signed