How does hard drive formatting work?

Question

What exactly happens when you format/wipe a hard drive ? Is it overwritten with random data or something else ? Is the format process the same for all types of hard drives and for all brands ? Also, will it be harder to recover data from my hard drive if I format is repetedly, like 15-20 times ?

Solution 1

You do not format a disk. Instead you format the filesystem on that disk (whole disk) or on a partition on the disk.

Just what gets written to that filesystem depends on which FS you are formatting and which program you use for that. For windows there already is an answer in this post.

I assumed windows because other operating systems use different names for what is known as 'formatting' in windows. E.g. Mac OS (classic) used to 'initialise' a disk. ON unix like OS's the command is often mkfs (make filesystem).

Solution 2

Standard formatting is deleting only partition table (indexes to data clusters)

This is almost independent in sense of OS on windows is the FORMAT C, on a Mac it is disk utility

For more serious deleting the entering of zeros or ones, or random entry, is done in several passages

The formatting mechanism is different for HDD and SSD

On SSD there is no need to do the additional format with zeros and ones because the nand memory is initialized unlike the magnetic disks where there is a possibility to reconstruct if it is not done by some random pattern standard like DOD or NIST standards for deletion (see http://en.wikipedia.org/wiki/Data_erasure)

For windows you can use http://zilla-data-nuker.en.softonic.com

On a MacOS use secure erase option

All secure erase options can last several hours even days depending on the algorithm

Comments

[Synetech]

What exactly happens when you format a drive? It erases the file pointers and optionally erases the clusters as well. Does it overwrite with random data or something? It depends on formatting the program. Most offer a “quick format” which only erases the pointers and a full which writes blank data to clusters. Is the format process the same for all types of hard drives and for all brands? More or less. Also, will it be harder to recover data from my hard drive if I format is repetedly, like 15-20 times? Not generally; once is enough, but only if it’s a full format, not a quick-format.

[ganesh]

Not to be confused with the MBR partition table.

[Steam]

better. use CCleaner for internal and external hard drives.

[Jamie Hanrahan]

Sorry but formatting in modern contexts refers to creating a file system structure in an existing partition. NOT to deleting or creating partition table entries (that's called "partitioning"). Hard drives do not (except for testing or security purposes) ever need to be "formatted" with zeroes or ones, no more than do SSDs. Yes, in ancient times (i.e. ST506 or ESDI drives) we would do a "low level format" on HDs, which meant writing the track and sector preambles... that isn't even possible to do in the field any more; if you somehow lose the LLF, it can only be re-done at the factory.