Where are checksums stored?

I did try to search for the answer but didn't have any luck.

When a checksum is calculated a new column appears and displays the checksum. Where are those checksum stored? In the file, in Opus, somewhere else?

And depending on the answer to the previous question, is there a command to recalculate the checksum and compare it to the previous 'stored' value?

I guess, they are not stored at all, but created on the fly. But you can create CSV style lists in Opus 13 and use some Diff tool.

The only time checksums are stored automatically is when using the Duplicate File Finder with the "use MD5 cache" option turned on.

Checksums displayed in columns aren't stored anywhere.

EDIT: Correction, GetSizes USEHASHCACHE can also store them in the filesystem, via NTFS ADS. https://www.gpsoft.com.au/help/opus12/index.html#!Documents/GetSizes.htm

If you want to calculate checksums and then re-calculate and verify them later, tools like QuickSFV, TurboSFV or QuickPar are probably the way to go. There are also some Opus scripts for doing similar, but those tools have nicer UIs and are free, so they're what I'd go with.

I do have a utility I currently use but was just checking if Opus could replace it and simplify matters. I'll check these out to see if they are more flexible than what I'm using. Thanks.