The TRIM function regularly deletes the unused space on SSDs while the CPU/IOs are not too busy.
This is where the TRIM function of a system comes in play. This means with time the writing speed of SSDs starts to slow down drastically. In SSDs the technology demands that the old data be first erased before new data will be written, which slows down the writing time. With rotating hard disks, the new data is simply written in the available space without having to erase the old one before. That is where SSDs and rotating hard disks differ. When it is used again the new data will overwrite the old one.
So the space that is been made available again will soon or later be used again as we would expect. That is why sensitive information should always be overwritten by something instead of simply erased… but that is another subject.
In normal hard disks when a file or directory is been erased, in fact the space used by the file or directory is simply put back on the unused space list. Did you just buy an SSD for your MAC running Lion and would like to get the best of it? A short explanation:
