Most of these answers are mostly right: deleting a file on disk doesn’t actually erase the data, it just marks the space as available to write over - meaning that so long as nobody’s used the space since, you can go retrieve the contents with an undelete utility.
Most of the time, people don’t care - but if for instance you’re selling the PC or there’s highly sensitive information involved, that might not be good enough.
As such, there are utilities that can go out and specifically overwrite the contents of a file with all zeroes, so ensure that it’s dead-dead - and there are other utilities that can do the same to an entire disk.
There’s one wrinkle: Magnetic HDDs don’t reliably erase and overwrite completely in a single pass; just like rubbing out pencil writing, it can leave faint impressions under the new content, and it is actually possible (with serious effort by forensic recovery people) to glean some of the previous content. If there’s serious money / security at stake, a simple overwrite is not enough, so there’s software that certifiably-randomly scribbles over each bit, seven times over, making the chances of recovering the original astronomically slim. Again, this can be done for individual files or the entire disk.
SSDs aren’t prone to leftover impressions, thankfully - what’s gone is gone. And they have one other neat feature: while a magnetic disk can only be erased one bit at a time, so large disks can take hours - SSDs can just open the floodgates and ground every cell at once, fully erasing the entire disk in an instant.
This instant-erase, while comprehensive… returns before you’ve even taken your finger off the ENTER key, so fast it feels like it can’t possibly have done anything, it must be broken, how can I trust it? So BIOS manufacturers hype it up, call it something impressive to underline that it’s big and powerful, and actually impose a 10-second countdown to make it feel like it’s doing something complicated.
Any of these different things have been called ‘secure erase’ at various points, so it’s a little context dependent. But from the end-user perspective: this data is getting shredded then incinerated then added to cattle feed; it’s not coming back.
There’s one wrinkle: Magnetic HDDs don’t reliably erase and overwrite completely in a single pass; just like rubbing out pencil writing, it can leave faint impressions under the new content, and it is actually possible (with serious effort by forensic recovery people) to glean some of the previous content.
No, it’s not. At least it has never been done on more than single bits, with an accuracy higher than 50% (which means even when trying to restore a single byte, your chances of it being correct are 1/256).
Most of these answers are mostly right: deleting a file on disk doesn’t actually erase the data, it just marks the space as available to write over - meaning that so long as nobody’s used the space since, you can go retrieve the contents with an undelete utility.
Most of the time, people don’t care - but if for instance you’re selling the PC or there’s highly sensitive information involved, that might not be good enough.
As such, there are utilities that can go out and specifically overwrite the contents of a file with all zeroes, so ensure that it’s dead-dead - and there are other utilities that can do the same to an entire disk.
There’s one wrinkle: Magnetic HDDs don’t reliably erase and overwrite completely in a single pass; just like rubbing out pencil writing, it can leave faint impressions under the new content, and it is actually possible (with serious effort by forensic recovery people) to glean some of the previous content. If there’s serious money / security at stake, a simple overwrite is not enough, so there’s software that certifiably-randomly scribbles over each bit, seven times over, making the chances of recovering the original astronomically slim. Again, this can be done for individual files or the entire disk.
SSDs aren’t prone to leftover impressions, thankfully - what’s gone is gone. And they have one other neat feature: while a magnetic disk can only be erased one bit at a time, so large disks can take hours - SSDs can just open the floodgates and ground every cell at once, fully erasing the entire disk in an instant.
This instant-erase, while comprehensive… returns before you’ve even taken your finger off the ENTER key, so fast it feels like it can’t possibly have done anything, it must be broken, how can I trust it? So BIOS manufacturers hype it up, call it something impressive to underline that it’s big and powerful, and actually impose a 10-second countdown to make it feel like it’s doing something complicated.
Any of these different things have been called ‘secure erase’ at various points, so it’s a little context dependent. But from the end-user perspective: this data is getting shredded then incinerated then added to cattle feed; it’s not coming back.
No, it’s not. At least it has never been done on more than single bits, with an accuracy higher than 50% (which means even when trying to restore a single byte, your chances of it being correct are 1/256).