Atari never produced hard drives for the 8-bit Atari, but the following
were produced and marketed to Atari users by third parties.

==> Corvus hard drive (5MB, 10MB, or 20MB)
(some Corvus info from an eBay auction by Ben Corr, 7/03)
Attaches via joystick ports 3 & 4 on the Atari 800 only.
  -- Corvus Integrator Board - allows access to the Corvus Disc without the
     Corvus software, so that any DOS that uses standard SIO calls will work.
  -- Corvus Multiplexer - used to network up to 8 Ataris to one Corvus Drive
  -- Corvus Mirror card - back up the drive's contents onto video tape

==> SupraDrive Atari Hard Disk, by Supra, later K-Products. 10MB or 20MB.
includes external Hard Disk Interface
Some limitations on drive type and size and total number of drives in sys.
Attaches via PBI, or ECI with adapter.
See: http://www.atarimagazines.com/v5n6/Supradrivefor8Bit.html

==> BTL Hard Disk System by Lurie Associates
10MB to 128 MB
BTL 2001 Connector for 600XL/800XL PBI
BTL 2002 Connector for 130XE/800XE/65XE ECI
BTL 2004 SASI Hard Disk Adapter
See: http://www.atarimagazines.com/v5n12/BTLHardDisk.html

Most hard drives are connected to the Atari via a SCSI or IDE interface.
Such interfaces are covered in other sections of this FAQ List.