An interesting feature that exists in many SSDs is the ability to quickly erase all the data on the device. The military is especially interested in this feature because it helps prevent sensitive data from falling into the wrong hands.
For example, let’s say your helicopter crashed when on a mission to assassinate the leader of a major terrorist organization. If the HDD or SSD inside the cockpit was recovered by that organization the data might be extracted to help undermine future missions.
Since SSDs use multiple NAND flash chips, each flash chip can be given erase instructions at the same time as all the others. This is illustrated in the diagram at the top of this post, which was borrowed from an Objective Analysis report: Solid State Disk Market Outlook. (This report can be purchased for immediate download on the Objective Analysis website.) In an HDD, on the other hand, each track must be erased by the device’s only head mechanism one track at a time. This means that SSDs can be erased in seconds, while an HDD might take several minutes to erase. Power may not be available long enough to erase the HDD.
Some SSDs even perform a repeating routine of erase/over-write/erase in order to destroy any ghost images of data that may remain after a block has been erased. The SSD Guy even knows of one drive that remains in this state even after power is removed – when power is re-applied the SSD goes back into secure erase mode ad infinitum.
SSDs had this advantage over HDDs for a number of years, but more modern self-encrypted HDDs can now perform an instantaneous erase simply by obliterating the HDD’s encryption key. This is a very fast operation that renders all information on the HDD completely illegible. The same is true for self-encrypted SSDs.