TRIM tells the SSD that the blocks in question are free and open to writing. The SSD will erase them (it sets all the cells to 1) when it sees fit, usually not immediately.

Greetings Ars Hive mind. I just replaced the 1TB 7200rpm hdd with in my mid 2012 non-retina MBP with a Crucial M500 960Gb SSD about a month ago and I was wondering about the issue of TRIM. I seen ...