Can i latch on by asking if all roms require CHD's to work?
NO..... CHD's are compressed hard drive images, from games that had a hard drive containing things like the game program and graphics and sounds etc etc.
Not all games had a hard drive in them. Many had all of their program solely contained in the ROM's
However, if you are trying to run a game that had a hard drive in the original arcade machine then you must have the ROM's and The CHD.
The downside to all of this is that, not many of the CHD games run well or at least not at full speed inside of MAME and many of them don't run at all.
Best Regards,
Julian (Fozzy The Bear)