TRIM support allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. If it's off, you may see significantly slower drive writes. This feature is supported on official Apple drives but not on third party drives. A tool called TRIM Enabler previously allowed users to enable support for their own SSDs; however, Yosemite made changes which forced you to disable kext signing to turn on TRIM and if your NVRAM or PRAM gets reset your system refuses to boot.
Notably, with the release of OS X El Capitan, forum members have been investigate possible support for TRIM and thankfully found that if "rootless" is disabled, a simple "trimforce enable" command will turn on TRIM for third party drives.
The developer of TRIM Enabler has confirmed this method works and plans to update the software to support it. This is good news for users as long as Apple continues to allow you to disable its new "rootless" security enhancements.
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Read More [via MacRumors]