Released in 1983 as a replacement for the 800 and 1200XL, the 800XL is the
high-end version of the 600XL.  The 600XL/800XL include most of the features
of the 1200XL, minus the 4 Function keys, the 2 LED lights, and the "ATARI"
logo screen.  But both the 600XL and 800XL have the Atari BASIC language
built-in.  In addition, these two systems offer the Parallel Bus Interface
(PBI), providing fast parallel access to the heart of the computer.  The 800XL
contains 64K RAM.

Boot options:
   Atari BASIC (Rev. B or Rev. C, see below)
      - Turn on computer with no cartridge inserted and no powered disk drive.
   Self Test program
      - Hold down [OPTION] while turning on the computer with no cartridge
        installed and no powered disk drive.
   Cartridge
      - Turn on computer with cartridge inserted.
   Cassette 
      1. Hold down [START] while turning on the computer.  
         (System buzzer sounds.)
      2. Press [PLAY] on the program recorder.
      3. Press [RETURN] to load and run cassette program.
   Disk, with Atari BASIC enabled
      - Turn on computer with disk inserted in powered disk drive.
   Disk, with Atari BASIC disabled
      - Hold down [OPTION] while turning on computer with disk inserted in
        powered disk drive.

Box: "More Memory Means More Power"

Versions of the Atari 800XL:

  o  NTSC (North America) version, produced fall 1983 to summer 1984 by
     Atari, Inc.
     - Monitor port lacks the chrominance video signal on pin 5
     - TV Channel switch: 2 - 3
     - Atari BASIC Revision B
     - Made in Hong Kong and Taiwan.
     - Some internal pics:
       http://atarinside.dyndns.org/gallery2/main.php?g2_itemId=74

  o  PAL (Europe) version, produced fall 1983 to summer 1984 by Atari, Inc.
     - Monitor port lacks the chrominance video signal on pin 5
     - No TV channel switch
     - Atari BASIC Revision B
     - Visual tour: http://www.atari800xl.eu/public/800xlpal/
     - More internal pics:
       http://atarinside.dyndns.org/gallery2/main.php?g2_itemId=73
     - Made in Hong Kong and Taiwan.

  o  PAL (Europe) version, produced fall 1984 by Atari Corp.
     - "800XLF" motherboard
     - FREDDIE memory management chip
     - Earlier production: Monitor port lacks the chrominance signal on pin 5
       Later production: chrominance signal is present on Monitor port pin 5
     - No TV channel switch
     - Atari BASIC Revision C
     - Made in Taiwan.

  o  SECAM (France) version, produced fall 1984 by Atari Corp.
     - "SECAM ROSE" motherboard
     - FREDDIE memory management chip
     - FGTIA, paired with the PAL ANTIC
     - Monitor port has unique pinout, 6 pins instead of 5;
       includes composite video but not chrominance nor luminance signals
     - No TV jack
     - No TV channel switch
     - Internal color/monochrome switch 
     - Atari BASIC Revision C
     - Visual tour: http://www.atari800xl.eu/public/800xlsecam
     - More internal pics: 
       http://atarinside.dyndns.org/gallery2/main.php?g2_itemId=15
     - Made in Taiwan.

5 different types of 600XL/800XL keyboards were nicely documented by Beetle
here: http://www.atariage.com/forums/index.php?showtopic=105170

Production of the 800XL was discontinued by 1985.