First, I have to thank Lightning for making an excellent product, that puts a lot of the expensive CD/DVD burners to shame. Even when I find a particular operation difficult at first, I end up finding a common sense way to do it, unlike a lot of other software in general, especially software from Microsoft. I'm asking my question here because I'm pretty sure I'll find someone here with the knowledge to answer it, and give a straight answer without corporate censorship.
My guess is that some of you are familiar with nlite, a free tool that customizes a Windows installation disk so that you can remove Windows components, as well as incorporate system updates.
The first step of the process is to copy all the files on a Windows installer CD to a disk drive so that nlite can make the changes you specify. In the process of doing that, I noticed that the folder containing the files from the CD was much larger than the total size of the CD as reported in Properties. In fact, before I did any copying, the total size of the two largest folders on the CD were much larger than the total CD size.
If I use ImgBurn to make an ISO image of the original CD, the size of the ISO file matches the size of the CD, so it can be burned to make an exact copy. But if I copy all the files to a disk drive first, the total size of these files is much too large to fit on a CD, and I get a warning message.
(The XP installer I'm using is a recent one from HP, which is made for a particular model of computer, which comes out of the factory with an XP license tag on its case. So there's no pirating; the CD's are sold inexpensively, because they're associated with an already-paid-for OEM XP license.)
I'm guessing that there is some kind of strange compression going on, but I don't know how it works, or if there's any way around it, so I can make an updated installer and avoid manually installing Service Pack 3 and about 100 update files. The same size discrepancy appears with the CD viewed in Windows 2000 and XP. It's not related to a few MB of wasted space because of large cluster sizes on the disk drive; the difference is about 650 MB vs. 900 MB, and it appears when looking at the folders on the CD itself.