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zeppo ,
@zeppo@lemmy.world avatar

Because of how filesystems work. There’s basically an index that tells the OS what files are stored where on the disk. The quickest way of deletion simply removes the entry in that table. The data is still there, though. So a data recovery program would read the entire disk and try to rebuild the file allocation table or whatever by detecting the beginning and ends of files. This worked better on mechanical drives than SSDs.

pearsaltchocolatebar ,

Yup, and many security suites will include a tool that writes all 0s or garbage to those sectors so the data can’t be recovered as easily (you really need multiple passes for it to be gone for good).

zeppo ,
@zeppo@lemmy.world avatar

right, i’m super out of date but you;d want to do shred or some dd dev/random > device thing to securely erase them.

CameronDev ,

You have a notebook. On the first page, you put a table of contents. As you fill in pages, you note them down in the table of contents at the start.

When you want to delete a page, instead of erasing the whole page now (there are hundreds free still, why waste the effort), you erase the entry in the table of contents.

Now if someone finds your notebook, according to the table of contents there is no file at page X. But if they were to look through every single page, they would be able to find the page eventually.

This is loosely how file systems work. You can’t really use it to boost storage, the number of pages is finite, and if you need to write a new page, anything not listed in the contents is fair game to be overwritten.

lurch ,

it’s inefficient to really erase the data, so what happens usually is: it gets marked as deleted. the data only gets overwritten when another file is written in the same data area, which often doesn’t happen immediately. even if a drive gets formatted the empty metadata structures of the new partitions and file systems are just written on top. since they have no file entries yet, the previous data just sits there invisible and inaccessible until new files are created and maybe overwrite a bit of the old data.

transientpunk ,
@transientpunk@sh.itjust.works avatar

Often times when you delete something off a computer, the computer simply deletes the address of the data, but doesn’t overwrite the data.

Think of a map for a city. If you delete a house off the map, you may not be able to find it anymore, but the house is still there. It’s the same for computer storage

jimmydoreisalefty ,
@jimmydoreisalefty@lemmy.world avatar

IIRC: Data has not been overwritten yet; it is just shown to be open to being rewritten.

It can still be recovered with minimal corruption if the device was not used too much, where open storage would be eriten over.

over_clox ,

eriten

hddsx ,

No, there is no way to store more stuff on PCs.

Hard drives are devices that store 1’s and 0’s. There’s a bit more complication, but the short answer is that you can wipe a file system, but the files are still there.

bradsmybro ,

From my limited understanding deleting something on a hard drive is just letting your computer know that that space is now available for other data to be stored there. Until something is actually stored there the data isn’t changed.

You can’t use this to increase storage in a computer because the total amount of data allowed on a hard drive doesn’t change when data is deleted. It just moves that stored data to the available section.

muntedcrocodile ,
@muntedcrocodile@lemm.ee avatar

Cos ur computer is lying to u. When u delete a file it doesnt actually delete it it just marks that section of disk as deleted that will eventually be overwritten at some point in a future.

TESTNET , (edited )

Because as long as it isn’t overwritten it can sometimes reside in a residual way in the storage sectors on the drive, these hdd scanning software’s check through the sectors for data hiding in them some sucxessfully some not as successfully, there for some will find more or less data than others do as well.

This is why data disappears on drives as well when a physical issue causes the sectors of the drive to begin to stop working aka “bad sectors” this makes the data start to seemingly magically vanish or corrupt if it’s still operating and booting into Windows you can at times witness the data/folders and or files present in folders one moment and missing fron the OS the next, that’s an indictator often of an imminent drive failure due to bad sectors. In this scenario it get’s less likely you’ll recover the data the longer the drive is in use because more of the sectors will probably die. You want to be doing the recovery and not using the drive in Windows in this instance. I say Windows but it applies to any HDD with any OS installed really.

SnotFlickerman ,
@SnotFlickerman@lemmy.blahaj.zone avatar

The only way to truly securely delete data is disc destruction. Remove the drive and drill through the hard disk platter or the SSD memory chips.

FuglyDuck ,
@FuglyDuck@lemmy.world avatar

Even a single overwrite process is sufficient to stop most attempts at recovery- the only people who might be able to reconstruct that data are… like top FBI forensic labs, and similar.

Even then, most of the data would be coming back corrupted and mostly useless.

2 or 3 overwrites are sufficient to prevent that as well.

For SSD’s, a single overwrite renders it impossible, simply based on how the data is physically stored- there’s no residual “footprint” or “ghost”- the NAND flash memory used floating-gate transistors to store the data. Either the gate is flipped or it’s not, there’s no way to know if it was previously flipped, only what its current state is.

Physical destruction is usually only recommended for extreme cases, where that drive held extremely sensitive data- where the consequences of any amount of that data being recovered would be catastrophic, even then the process begins with overwriting data. (Also keep in mind just breaking the platers aren’t enough- they have to be shattered into ittybitties.)

orcrist ,

Generally speaking, writing new data is what actually erases old data. So no, you can’t exploit it for extra storage space.

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