In the old days, when you wanted to replace your hard drive with a larger one, you performed a "secure erase" to completely eliminate any personal data. This would write zeros across the disk, overwriting anything that was already there.
But now, thanks to advances in storage technology, this no longer works. (It's not that he can change his own Mac SSD now anyway.) The new secure erase, says Apple, is simply encrypting your disk.
What's wrong with simply throwing everything in the trash?
Computers not really, you delete a lot when you move your files to the trash. They simply pretend that those files are no longer there, marking the space they occupy as free. Then, at some point in the future, those bits may be overwritten with new bits, from a new file. This is how recovery software works. It allows you to find your deleted photos, as long as nothing has been written about them since you "deleted" them.
Secure deletion writes data about those orphaned files (one to 35 times on the Mac) until they can no longer be recovered But in the Apple Disk Utility manual (available for reading in the Mac Terminal application By typing
man diskutil ), you can read why Apple no longer considers this approach safe:
NOTE: This type of erase security is no longer considered secure because modern devices have cache hardware that levels wear , save blocks and possibly persist.
The modern solution to erase your data quickly and safely is strong encryption, with which the simple destruction of the key is more or less instantaneously makes your data irrecoverable in practical terms.
Hard disk security: encryption vs. secure erase
An encrypted disk cannot be read at all without the key to unlock it. And if you delete that key, all that remains is the encrypted data, which is simply unintelligible nonsense.
The storage of your iPhone and iPad is encrypted by default, so you can use Clear all content and settings (in General> Reset in the configuration application ) to erase Your iOS device instantly. This is very useful when repairing the iPhone, for example. It means you can continue using your iPhone until you deliver it, and then delete it in a few moments. (Just make sure you have a current backup to restore.)
On Mac, you must enable FileVault to get full disk encryption. However, if you set up a new Mac from OS X Yosemite, you probably already have. In Yosemite, Apple ticks the box to enable FileVault during the configuration process. For not to use FileVault, it must be explicitly excluded. This is good for almost everyone, in most cases. In fact, between that and the T2 security chip, the Mac is almost as impervious to a practical attack as the iPhone and iPad.
So, to summarize: don't bother to erase your Mac disk safely. Instead, be sure to encrypt it from the beginning.