Section includes contributions by Andreas Koch, TXG, KMK

The Atari Disk Drives provide storage and retrieval of programs
and data on 5.25" floppy disks.

==> Atari 810  ---  a 5.25" floppy disk drive
The least common denominator for the Atari.  One mode of operation:
1) Single-Sided, Single-Density--
  FM   40 tracks  x  18 sectors/track  x  128 byte/sector  =  90K capacity
The 810 drive has only one drive head, so it can only read/write to one side
  of the disk.  The reverse side of a 2-sided "flippy" disk may be used by
  inserting the disk into the drive upside-down.
19.2Kbps transfer rate.  288RPM.
The 810 includes a 6507 microprocessor.
Shipped with DOS I (1980-1981) or DOS 2.0S (1981-1983)
MPI version (1980-1982): push button, entire door slides up for disk access
Tandon version (1983): door center flips open for disk access
two SIO ports
Production of the 810 ended in May 1983.
accessories from Atari:
CX8100 Atari 810 Blank Diskettes (5 per box)
CX8111 Atari 810 Formatted Diskettes II (5 per box)
CX8202 Atari 810/815 Blank Diskettes (5/box, certified for double density)

Third-party upgrades for the 810:
810 Archiver -- copy many copy-protected programs
810 Fast Chip by Binary  10%-40% faster
810 Turbo (810T) by Neanderthal Computer Things (NCT) -- double-density,
                track buffering, speed comparable to Happy 810 Warp Speed
Happy 810 -- Happy Backup, Warp Speed 52Kbps, 18 sector buffer

==> Atari 815 Dual Disk Drive  ---  dual 5.25" floppy disk drives in one unit
Were produced (all hand-built), but are very rare.  One mode of operation.
Per drive:
1) Single-Sided, Double-Density--
  MFM  40 tracks  x  18 sectors/track  x  256 bytes/sector  =  180K capacity
The two drives in the 815 have only one drive head each, so each drive can
  only read/write to one side of the disk.  The reverse side of a 2-sided
  "flippy" disk may be used by inserting the disk into the drive upside-down.)
19.2Kbps transfer rate.  288RPM.
The 815 includes a 6507 microprocessor.
Shipped with DOS 2.0D
MPI mechanism version- push button, entire door slides up for disk access
Tandon mechanism version- door center flips open for disk access
The 815 was designed by Paul Mancuso and Levon Mitchell. (Atari History Museum)
accessories from Atari:
CX8202 Atari 810/815 Blank Diskettes (5 per box, certified for double density)
  Stephen Knox writes (12/28/02):
  I believe the story on the 815s was Atari didn't want to release them due to
  severe QA problems with the drive but they had so many preorders they had to
  release something.  I think they filled the preorders and then cancelled the
  model - Most of them got returned due to problems.

==> Atari 1050 Dual-Density Disk Drive ---  a 5.25" floppy disk drive
Same as the 810, plus Dual-Density capability.  Two modes of operation:
1) Single-Sided, Single-Density, 90K, 810 compatible
2) Single-Sided, Dual-Density, otherwise known as "Enhanced Density" because
  it is not true double-density--
  MFM  40 tracks  x  26 sectors/track  x  128 bytes/sector  =  130K capacity
The 1050 drive has only one drive head, so it can only read/write to one side
  of the disk.  The reverse side of a 2-sided "flippy" disk may be used by
  inserting the disk into the drive upside-down.)
19.2Kbps transfer rate.  288RPM
The 1050 includes a 6507 microprocessor.
Shipped with DOS 2.0S (1983), DOS 3 (1983-1985), or DOS 2.5 (1985-1988)
DIP switches:    Black & white left: Drive 1
            Black right, white left: Drive 2
            Black left, white right: Drive 3
                Black & white right: Drive 4

Third-party upgrades for the 1050 (all add a true SSDD 180K capability):

1050 Duplicator       SS SD/ED/DD "read 18 sectors in the time normally for 1"
  (Duplicating Technologies (DT))
  sources(Jim Patchell)http://www.oldcrows.net/~patchell/atari/duplicator.html

Happy Warp Speed and compatible:
-------------------------------
Happy 1050            SS SD/ED/DD Warp Speed 52Kbps, 36 sector buffer,
  (Happy Computers)   Happy Backup. also read/write 180K 5.25" MS-DOS floppies
CheerUp Upgrade       SS SD/ED/DD Warp Speed 52Kbps (Happy clone)
  (Happy Computers, converts 1050 Duplicator to Happy 1050)
Hyper Drive (Chaos! Computers)
                      SS SD/ED/DD Warp Speed 52Kbps (Happy clone)

UltraSpeed and compatible:
-------------------------
US Doubler (ICD)      SS SD/ED/DD UltraSpeed (US) 54Kbps, sector skewing
Mini-Speedy           same as Speedy 1050, but without displays & speaker
  (Compy-Shop, now ABBUC)
Speedy 1050           SS SD/ED/DD UltraSpeed 70Kbps  8kB buffer,
  (Compy-Shop, now ABBUC)  DOS, copier, track & density displays, beep speaker
  http://www.mia-net.org/speedy.html
Super Archiver (CSS)  SS SD/ED/DD UltraSpeed 54Kbps (US Doubler clone)
Super Archiver II(CSS)SS SD/ED/DD UltraSpeed 54Kbps (US Doubler clone)
SuperMax 1050         SS SD/ED/DD UltraSpeed 52Kbps
Super Speedy          upgrade for Mini-Speedy, same specs but adds switches
  (Compy-Shop, now ABBUC)  and an LED display


1050 Turbo and compatible:
-------------------------
1050 Turbo            SS SD/ED/DD Turbo speed 68.2Kbps
  (Bernhard Engl, 1986) Backup software (name?). option: printer interface
Top Drive 1050        SS SD/ED/DD Turbo speed 68.2Kbps (1050 Turbo clone)
TOMS Turbo            upgrade for 1050, LDW/Indus, and CA-2001:
                      adds 1050 Turbo speed (68.2 Kbps) and IBM densities

Add support for multiple above enhancements:
--------------------------------------------
I.S. Plate            SS SD/ED/DD Ultra/Warp (USD/Happy clone)
  (Innovated Software)
Lazer 1050            SS SD/ED/DD Warp Speed and UltraSpeed 54Kbps
                      (USD/Happy clone)
TOMS Multi            upgrade for 1050, LDW/Indus, and CA-2001:
                      adds 1050 Turbo (68.2 Kbps) and UltraSpeed (54 Kbps),
                      and supports IBM densities

Rich Mier professes:
You've been plugging and unplugging the SIO cable with the 1050 power pack
plugged in, right?  That's a no-no.  Most of the time it's okay, but about 1
in 10, 20 times, it will blow out 'U-1'.  It's a CA/LM 3086 I.C. at the right,
rear of the main board.  A 14 pin DIL chip.  Actually it is an array of 5
transistors.

Unplug the power pack from the 1050, then unplug the SIO cable.  Power can be
ON on the CPU.  The problem has to do with the secondary winding of the Power
Pack.  Remember, the problem only occurs 1 out of 10 - 20 times that you do
it, not all the time.

It doesn't really matter if the 1050 Transformer has power on or off, it
'Might' happen if plugged into the 1050.  It is really bad on 810's.

One thing, if the system has been turned off for, oh say, 5 - 10 minutes it
won't matter.  By then all the capacitors should be bled(sc?) to 0 volts.

==> Atari XF551  ---  a 5.25" floppy disk drive.  Four modes of operation:
1) Single-Sided, Single-Density, 90K, 810 compatible
2) Single-Sided, Enhanced-Density, 130K, 1050 compatible
3) Single-Sided, Double-Density, 180K, Percom & other 3rd parties compatible
In the above 3 modes, the XF551 reads/writes to only one side of the disk.
  The reverse side of a 2-sided "flippy" disk may be used by inserting the
  disk into the drive upside-down.  But note:
    Chinon-built XF551--CANNOT read/write/format disk backside if the disk has
      no 2nd timing hole
    Mitsumi-built XF551--CAN read/write disk backside if the disk has no 2nd
      timing hole, but CANNOT format the backside without the 2nd timimg hole.
  The two types of XF551 drives are externally identical.
4) Double-Sided, Double-Density--
  MFM  80 tracks  x  18 sectors/track  x  256 bytes/sector  =  360K capacity
In this double-sided mode, the XF551 utilizes a 2nd drive head to read/write
  to the 2nd side of the disk.  The XF551 writes "backwards" to the second
  side of the disk, when compared to a two-sided "flippy" disk with SSDD 180K
  format on each side.
High speed 38400 bps burst mode usable only with SpartaDOS X, SuperDOS 5.1,
  TurboDOS, DOS XE, and patched SpartaDOS 3.2.
Rotation rate: 300RPM.  Since all other Atari-specific drives run at 288RPM,
  this results in rare compatibility issues.  Specifically, these commercial
  disks do not load in, and can be damaged by, the XF551:
  - Flight Simulator II (subLOGIC)
  - Blue Max (Synapse)
  - Bank Street Writer (Broderbund).  Conflicting reports about this one.
8040 cpu +  external ROM or 8050 cpu with internal ROM
Shipped with DOS 2.5 (1988-1989) or DOS XE (1989- ).
DIP switches:    Both dips down: Drive 1
            Left down, right up: Drive 2
            Left up, Right down: Drive 3
              Left and Right up: Drive 4
The key engineer/designer of the XF551 was Jose Valdes at Atari
Third-party upgrades for the XF551:
CSS XF Single Drive Upgrade--3.5", 720K floppy drive replacement
                       also read 720K 3.5" MS-DOS disks
                       see http://www.nleaudio.com/css/products/XFsingdrup.htm
CSS XF Dual Drive Upgrade--add 3.5" drive w/o losing the 5.25" drive
                       also read 720K 3.5" MS-DOS disks
                       see http://www.nleaudio.com/css/products/XFdualdrup.htm
CSS XF551 Enhancer--overcomes sensor for index hole, create flippy disks
                         see http://www.nleaudio.com/css/products/XF551enh.htm
CSS XF Update--replace drive OS, adds UltraSpeed
                         see http://www.nleaudio.com/css/products/XFupdate.htm
Hyper-XF--available for 5.25" or 3.5" floppy versions; uses sector skewing
aka          and UltraSpeed (but no track buffer!); can use disk partitions
HyperXF      (2 on 5.25", 4 partitions on 3.5") with mixed Densities (S/E/D)
             or standard 360Kbytes (5.25") / 720Kbytes (3.5"); can
             theoretically read/write ST/PC 720k disks (software is missing!)
             OS created by Stefan Dorndorf/Germany;
http://ftp.pigwa.net/stuff/collections/nir_dary_cds/Pictures2/035%20Hyper%20XF.jpg
XF-Speedy--replaces the 8040 CPU with a 65C02 + ROM + Memory