Q: What are .SFV files? What is a CRC32 checksum?
A: SFV = Simple File Verification. Basically it appears like this:
Initial D - Live Action Movie.sfv, which contains
; Using hkSFV on 11.29.2005 at 22:27:48
; 730357760 03:40.56 2005-11-21 Initial D - Live Action Movie.avi
Initial D - Live Action Movie.avi 0ac923f4
It says it's generated by hkSFV, file size, date, name, etc. And generated a CRC32 of 0ac923f4.
Some programs will automatically check SFV files when it unpacks an archive. SFV uses CRC32, which is an older and less accurate algorithm, but it is quite fast. A 700 meg file can generate a full CRC32 checksum in less than 2 minutes, even on an ANCIENT 400 MHz machine. On a modern machine, it should only take seconds.
Sometimes on Bittorrent, you may see the checksum embedded in the filename, like:
Where [E87966A3] is the CRC32 checksum.
Sometimes you may see alternate checksums, such as MD5, SHA1, and other algorithms. Those basically generate a longer checksum, and is helpful when you need to generate a short but unique ID based on the content of the file. Any change in the file, and the ID will change. Thus, they can be used as unique file ID, as well as a file integrity check.