ISO maker — folder to disc image

Yes, when you provide a boot image and tick Hybrid MBR. The output gets a valid El Torito record (for BIOS/UEFI from optical media) and a hybrid MBR so dd if=image.iso of=/dev/sdX produces a bootable USB.

Because an ISO stores everything in sectors of 2048 bytes and a file never gets to share one. A 100-byte file occupies a whole sector, and a file of 5000 bytes occupies three — so a folder of many small files grows noticeably, while a folder of a few large ones barely changes. Directory records, the Joliet name table and one UDF entry per file add a little on top. This is a property of the format rather than an inefficiency to be tuned away: it is what lets any reader find a file by seeking straight to a sector instead of parsing its way there.

Yes, because it is never assembled in memory. The image is made of references to your files plus a few megabytes of directory data, and with the save dialog it is written straight to the destination file — so the ceiling is free disk space, not RAM. The folder itself is only listed when you add it; the files are read once, while the image is being written.

Yes. UDF and Joliet keep names exactly as they are, capitals included; ISO 9660 alongside them carries short uppercase names for old systems. Two names that differ only in case, such as Readme.txt and README.txt, cannot sit side by side on Windows, so the second one is stored as “README (2).txt” and listed after the build.

Add a boot image and say whether it is for BIOS or UEFI; a valid El Torito boot record is then written into the ISO, which is the structure firmware looks for when it decides whether a disc can be started from. That covers optical media and virtual machines. For a USB stick there is the hybrid MBR option on top: it puts a partition table at the very front of the image as well, so the same file works both as an ISO burned to a disc and as something written byte-for-byte to a stick — which is how installer images are usually distributed today.

Yes. Pick the modified folder, keep the same volume label and build again — the new image is written from scratch, so it reflects the folder exactly as it is now.

Yes. Windows, macOS and Linux read the UDF layer: full names and files over 4 GB. Anything that knows only ISO 9660 — some players, car stereos, older systems — reads the Joliet or ISO 9660 layer of the same image, where names longer than 103 characters are shortened and characters like ? * : are replaced with “_”. After the build the tool lists every such name.

It goes into the image whole. UDF stores it as it is; in ISO 9660 and Joliet, whose size field stops at 4 GB, the same bytes are described as several consecutive sections, which Windows, Linux and 7-Zip join back into one file. A device that reads only plain ISO 9660 and does not understand sections may show just part of it.