[REQUEST] Embedded versions of MS-DOS or DR-DOS

I am looking for the embedded version of ms-dos which i know that ms-dos 5 and possibly versions of ms-dos 6 , had embedded versions, Microsoft had a kit available, I think it was just a software kit that allowed you to Rom ms-dos , I also know that DR-DOS also had a software kit that allowed its version with the ability to be in a rom, But i believe you needed the source code to be able to do it , which came with the software kit, which allowed you to customize the OS yourself for the ROM, which i'm not sure that ms-dos embedded, the software kit might have had the source code to be able to edit the source code yourself to customize the ROM. I know there are other compatible versions of DOS that are available in ROM like ROM-DOS. If anyone knows anything about these embedded versions of DOS, or has them , or knows if they can be on this site please respond.