That forensic article is a consequence of what I was referring to.
When you delete a file on a mechanical hard drive the physical contents of the file still exist on disk, so you can use tricks like these to recover deleted data.
When the drive is then told to write over these locations it doesn't matter that there is old data there and it writes the new data to the location.
SSDs however store data in pages, and while they can write directly to an empty page they can not write directly to a page that already has data in it. Instead, an SSD has to read the current data from the page, modify that data with the new data that it wants to be there, and write the new data to the whole page at once. This is called a read-modify-write operation and is a major reason why SSDs (even now) decrease in performance as they fill up.
The issue is that when you delete a file on disk there is no way for the SSD to know that those data blocks aren't important anymore (without TRIM). The controller of the SSD has to manage a full drive of data (even if you're only actually using some percent of it) and only figures out that a file was deleted when it is finally told to write something else to that location.
TRIM tells the SSD that a file was removed and allows a controller to recover that area to help maintain its performance.
When you delete a file on a mechanical hard drive the physical contents of the file still exist on disk, so you can use tricks like these to recover deleted data.
When the drive is then told to write over these locations it doesn't matter that there is old data there and it writes the new data to the location.
SSDs however store data in pages, and while they can write directly to an empty page they can not write directly to a page that already has data in it. Instead, an SSD has to read the current data from the page, modify that data with the new data that it wants to be there, and write the new data to the whole page at once. This is called a read-modify-write operation and is a major reason why SSDs (even now) decrease in performance as they fill up.
The issue is that when you delete a file on disk there is no way for the SSD to know that those data blocks aren't important anymore (without TRIM). The controller of the SSD has to manage a full drive of data (even if you're only actually using some percent of it) and only figures out that a file was deleted when it is finally told to write something else to that location.
TRIM tells the SSD that a file was removed and allows a controller to recover that area to help maintain its performance.
There is a really good discussion of this topic in this article from way back in 2009: http://www.anandtech.com/show/2829