9.3) What are the .DCM, .ATR, and .XFD file formats?

These are all filename extensions used to name files containing entire 8-bit
Atari floppy disk images.

DCM - Disk Communicator format.  Invented by Bob Puff,
      mailto:76702.1076@compuserve.com for his Disk Communicator 3.2 utility.
      Used when working with native Atari hardware.

ATR - Atari disk image format.  Invented by Nick Kennedy,
      mailto:nkennedy@cswnet.com for his SIO2PC project.
      Used when working with non-Atari hardware.

XFD - Xformer disk image format. Invented by Emulators Inc,
      mailto:emulators@msn.com for their ST Xformer emulator.
      Identical to ATR except without the 16 byte header.
      Used when working with non-Atari hardware.

PRO - APE ProSystem format.  Invented by Steven Tucker,
      mailto:classics@nacs.net for his APE ProSystem device.
      Used with APE, the Atari Peripheral Emulator.