If you replaced your Mac old hard drive with a new SSD HD, You need to enable TRIM to improve the performance of your solid state drive.
TRIM allows the operating system and the drive to communicate about which areas of the drive are considered unused and thus ready to be erased and rewritten to.
If TRIM is not enabled, users can see significantly slower drive writes as the drive begins to fill up.
Here’s how to turn TRIM on:
Make sure you’re logged into your Mac with an account that has Admin privileges. Next:
Now wait for the system to restart by itself and you’re done. TRIM should be enabled on your new HD.