How does Time Machine backup files that have changed? As I understand it Time Machine will create the folder structure and create a copy of all of the files that are to be included in the Time Machine backup during the first backup. After that a hard link is created during every subsequent backup for files that have not been changed.

The question that I have is how files that have been changed since the last backup are backed up in the subsequent backup. I thought that it copied the entire modified file to the TM backup, but it appears that that isn't how TM works and I was hoping for some clarification.

During a recent practice test that I took for ACSP 10.12 it asked if, for a 5MB file if it was modified such that the new version was 6MB, would the TM have a separate 5MB and 6MB file or would it backup the 1MB difference between the two files and just retain the 1MB addition in the most recent TM backup. I figured that, though it may take up additional space to have a separate copy of the 5MB version and the 6MB version, it would provide a safety net in the event that an early version were deleted or corrupted - effectively ruining every subsequent version of that file. But the practice test said that it just saves the 1MB difference.

I was just looking for some clarification to help improve my understanding. Thanks in advance for any help!
After the initial Time Machine backup of the entire volume, sans exclusions, Time Machine always backs up the entire file of each file that has changed or was created since the last backup, not just the changed part.