file size changing depending on equipment used?

[Mike Borlace]

I was doing a test recording before starting a short film and noticed that different pieces of equipment read different sizes for the same file, the smaller the file, the smaller the change.  This was happening to all my files, even though I wasn't making any changes to them. 

As an example, a stereo BWF file 11 minutes and 15 secs was:

-194 MB on my Tascam HD P2 recorder

-185 MB on my PC computer after a firewire transfer from the HD P2

-189 MB on a DVD-R after being burned on my computer

-190 MB on Protools v.7.3.1 at the post house

-185 MB on Final Cut Pro v.5.1.4. at the post house

Again, there was no editing or processing of the file inbetween readings, equipment seemed to be giving a different file size to the same file.  Has anyone else noticed this? Is there an explaination for what is happening?

[ptalsky]

It gets pretty technical, but a lot of it has to do with the way each drive is formatted.  When a drive is formatted it is broken down into pieces called sectors.  When a file is stored, it is generally not written to consecutive sectors (this is why drives often need to be optimized - because large files can be written in sectors all over the drive).  So, back to the question - sector size is not consistent on each drive.  If a file hits any part of a sector, often that entire sector is reserved anyway. So, even if the file is only using 1MB of a 32MB sector, the OS will report it as using the full 32MB.  But, if you copy the file to a a drive with sectors that are only 24MB, that 1MB file will be reported as 24MB.  See, it's easy, really.  :-)

Phil