What do chd files do?

[GoTheBunnies]

Hi guys,

New to MAME (as you can probably tell from the question), but what are chd files for?

I have a set of roms with matching chd files - where should the chd folder sit....directly under the roms folder? How does MAME know to look for the chd files (because the roms will run without them right?) - does it just know, or do I need to specify the folder location in the MAME setup somewhere?

Thanks

[dennislee13]

 CHD file is a compressed image of the hard drive used in an arcade cabinet used in arcade games as it requires more spaces.

[BobA]

Games that have CHDs will not run without them.  I have my CHDs in the ROM directory with each CHD file in a directory with the same name but there is a newer way to set them up and I have not changed mine.

[GoTheBunnies]

Games that have CHDs will not run without them.  I have my CHDs in the ROM directory with each CHD file in a directory with the same name but there is a newer way to set them up and I have not changed mine.

Ok well that answer tells me that I must have them in the right place, or the games wouldn't be running (and they are). I thought the games would run anyway, but obviously not.....

Thanks