Overburn CD's

[sfax]

I recently ran across a couple of CD's which were burned in a strange way. The data on the CD showed up as 846 MB (!) in Windows Explorer ... I have the ISO and I can burn it without any errors with my burner. And another thing ... when you copy the entire CD on the hard drive, the amount of data becomes 1.4 GB ! This difference is not due to the file system ... if I try to copy those files back on a blank CD, the burning software will report 1.4 GB and will refuse to start burning ... I'm thinking whoever burned that CD may have had a method to crosslink the files ( the CD contains the full CD's of 4 operating systems : Windows 2000 Pro, 2000 Server, 2000 Advanced Server and 2000 Datacenter ) ... Each OS has its own folder (about 350 - 400 MB each)... So my question is : how the heck did they do it? What software allows you to create such a CD? How can one stash 1.4 GB worth of files on one regular CD?