windows 10 - Where is data written to on a hard drive after a wipe?

I just used the "windows media creation tool" on a 1TB HD, and my drive was mistakenly wiped in the process. I did not read the warnings when using "windows media creation tool," so tried to use a hard drive with data, thinking that new files would just be added onto the current partition. The 1TB drive was formatted and repartitioned down to 31GB, and 4gb of windows 10 iso were written onto the drive.

Where on a hard drive is data written to after a wipe? Would the files be written onto previously unused areas, or does the write location move back to the first area?

Answer

First note that logical location (the block addresses used by the OS) doesn't always correspond to physical location (where those blocks reside on disk platters or flash memory). The disk is free to make its own decisions on how to translate between the two, as long as it remains invisible to the OS.

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With HDs, things like "previously unused areas" and "write location moving back" don't quite work – data is just written wherever the OS asks it to be written. That is, the same logical address (LBA) usually corresponds to the same physical location.

(SSDs, on the other hand, do keep track in firmware of which locations are "in use", which have been freed (using TRIM), etc. so if the OS writes twice to the same logical address, it will probably (I think?) get a different physical area every time.)

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The logical location is constrained by the partitions. If the app has set up a 32 GB partition that starts at the beginning of the disk, then new files were written only within those first 32 GB, and the rest of the terabyte should remain untouched.

(A real disk wipe tool would have erased the whole disk, but that's not what the Media Creation Tool does – it only cares about writing as much as it actually needs.)

Space inside the partition, however, is managed by the filesystem's allocation algorithm (which usually picks varying locations in order to avoid fragmentation), so new data could've been written nearly anywhere within those 32 GB.