Let's say we're talking about a 1 GB video file. It's copy-pasted from hard disk D1 to the hard disk D2, then from D2 to D3, and so on, all using Windows. If we continue this process for like 1 million times, what would the resultant file look like? Do error bits accumulate and finally corrupt the file?
Once a single-bit error is introduced into a file, the file is corrupt. File systems, disk drivers, and hardware on the disk itself have checksums, error correction codes, and facilities to detect bad sectors to limit the probability of write (or read) errors, but it's not 100% (but it better be close to 100%, otherwise my disk isn't reliable).
In general, the way to compute the probability of corruption:
Let's say the probability of a single bit error occurring during a file copy is P. (P should be really, really low, otherwise, the disk or media wouldn't be reliable).
And let's assume that a file has a size N measured in bits (e.g. a 1 GB file would be 8 billion bits or so).
So the probability of the first bit in the file not getting corrupted is: (1-P). And so it follows that the probability of all bits not getting corrupted during a transfer is (1-P)N
Now let's say you copy the file X times. Therefore the probability of the file not getting corrupted after X transfers is (1-P)NX. Or rather, the probability of corruption after X transfers is 1 - (1-P)NX