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

You're right that this extension isn't signed, but it does come from Apple and it can be loaded despite the missing code signature.

If check with kextutil in a shell this tells you some information not available in System Information, specifically:

> sudo kextutil JMicronATA.kext
Diagnostics for /System/Library/Extensions/JMicronATA.kext:
Code Signing Failure: not code signed
kext file:///System/Library/Extensions/JMicronATA.kext/ is in hash exception list, allowing to load

This "hash exception list" doesn't seem to be documented by Apple, but I think it explains the discrepancy here. For some reason Apple didn't want to sign this kext, but they do have some special exception built into the OS that will allow it to be loaded.

(Perhaps approach was taken because it'll be easier in the future to revoke that right? though just speculating.)