Way back when (in the 70's) DOS was an operating system that lived on a floppy disk. The Apple II, the Tandy TRS-80 models 1, 3, 16 and many other computer manufacturers of that time, used a type of DOS. The "DOS floppy disk" had to remain in the computer's drive for the system to stay working. (thus DOS "Disk Operating System") Parts of the OS would be retrieved from the DOS disk from time to time as needed. If you removed the DOS disk, the system would most likely hang or crash. So, a second and third floppy drive would be used for data and programs.
Newer DOS versions like MS-Dos, Dr-Dos ,IBM-Dos, FreeDOS and others can live on hard drives, CD's, Flash-Drives and will continue to work correctly without the need for a "DOS floppy disk".
In today's world a highly upgraded version of DOS lives mostly on CD ROM drives and USB flash drives. ( More articles with DOS on USB flash drives as we find them )
Way back when (in the 70's) DOS was an operating system that lived on a floppy disk. The Apple II, the Tandy TRS-80 models 1, 3, 16 and many other computer manufacturers of that time, used a type of DOS. The "DOS floppy disk" had to remain in the computer's drive for the system to stay working. (thus DOS "Disk Operating System") Parts of the OS would be retrieved from the DOS disk from time to time as needed. If you removed the DOS disk, the system would most likely hang or crash. So, a second and third floppy drive would be used for data and programs.