these items being committed to disk in sequential order.

Suppose a caching algorithm determines it would be fastest to write these items to disk in the order 4-3-1-2, and starts doing so, but the power gets shut down after 4 get written, before 3, 1 and 2, and so those writes never occur. When the computer is turned back on, the file system would then show it contains a file named XYZ which is located in sector 123, but this sector really does not contain the file. (Instead, the sector will contain garbage, or zeroes, or a random portion