Lightning UK,
Wow, quick response. You truly are a lightning!
Anyway,let me dismantle what you said so I can absorb the information much more clearly. Also to give you more details, those multiple iso images are created from scratch, except the ones I extracted from my CD installers. I will burn them to an ordinary single-layer DVD+R and I am planning to put many iso images in a single disk as most of them are below 4gb in size. So based on what you said, I can safely delete those .mds files unless I use a Blu Ray disc?
I use WinCDEmu to mount my iso files. I mounted my .iso file with and without the .mds file, and it was recognized as a CD disc (eventhough the description below is 'UDF'). I assume this is only normal because the iso file is around 300MB. So I guess based on this testing, I can safely delete the .mds file?
UPDATE: I also tried mounting a 4GB iso file which I created with a diff. software, and WinCDEmu recognized it as a CD disk also. I guess it's WinCDEmu's thing to recognize everything as a CD disc.
(I think the obvious answers to my inquiries are both 'yes', but I don't want to assume as I am not an expert on these matters. )