Why Are All Files Not Copied

[lugesm]

Just bought a new external hard disk and did a SuperDuper bootable backup that copied all files on my iMac hard drive.

Upon completion I noted that the "Get Info" on my iMac hard drive shows approximately 403MB more data than a similar "Get Info" on the backup drive. I suspect this is okay, but I have not found an explanation.

Is this to be expected? If so, can someone point me to an explanation, so that I might better understand the operation?

Thanks,
L