Are disk sector writes atomic?

Question

Clarified Question:

When the OS sends the command to write a sector to disk is it atomic? i.e. Write of new data succeeds fully or old data is left intact should the

Answer 1

I would expect one torn page to consist of part X, part Y, and part unreadable sector. If a head is in the middle of writing a sector when the power fails, the drive should park the heads immediately, so that the rest of the drive (aside from that one sector) will remain undamaged.

In some cases I would expect several torn pages consisting of part X and part Y, but only one torn page would include an unreadable sector. The reason for several torn pages is that the drive can buffer lots of writes internally, and the order of writing might interleave various sectors from various pages.

I've read conflicting stories about whether a new write to the unreadable sector will make it readable again. Even if the answer is yes, that will be new data Z, neither X nor Y.