The XE Game System was simply a repackaged Atari home computer.  The only difference between it and a normal 
Atari home 8-bit computer that could be purchased at the time was that it came with a light gun (which didn't exist 
before for the Atari), it had a detachable keyboard, and Missile command was built into the ROM set.  Missile command 
could be played by either detaching the keyboard or by hold the correct button down when the computer started up.

The computer was already capable of using a light pen and so the same code was used for the lightgun.

It used the 8-bit 6502 processor which always ran at 1.79... MHz.  The chip had 2^16 = 64k of byte addressable space. 
This is the same chip that was used in all Atari home computers, the Apple I & II, Commodore, Atari 5200 & 7800. 
Most importantly it was the processor of the sitemaps main competitor, the NES.

(Note: The Atari 2600 game system used the 6507 chip which was basically the same but instead had only 2^13 = 8k 
of addressable space.  It also had no VRAM and only 128 bytes of ram!)

Graphics were handled by the Antic chip which was a second CPU which ran its own special assembly commands. 
The two CPU chips had to access the same memory space.  VRAM could be anywhere in this space.  The XE game 
system had a palette of 256 colors (16 colors x 16 brightnesses), up to 16 could be displayed at once in a single graphics 
mode although graphics mode mixing to get more colors was easy and common.  Also, rudimetory sprites existed.  4 
that were 8 bits wide; 4 that were 2 bits wide.  Each spite was one color, but each could be a different color.  Sprites 
could be combined for multicolor characters.  Graphics were designed to be on a TV through a signal to channel 2 or 3 
converter or on a monitor that used RCA jacks, one for video and one for 8 bit mono sound.

Sound was handled by the Pokey chip.  It had 4 independent voice channels that could either play a variety of tones and 
buzzers or the two channels could be combined to play 4-bit wavetables!  It arguably had the most powerful sound 
processing of any 8-bit home PC.

The XE games system had 64k of RAM.  It had two joystick/ trackball/ dual-paddle/ lightgun/ lightpen ports.  They used 
the same type of plug as a IBM 9 pin serial port.  (Note:  The Atari 800 computer had four ports.) Custom joysticks were 
easy to make for the computer because one pin supplied power +5Vdc, and four of the other pins were used for up, down,
left, and right.  Two pins along with the +5Vdc and a 0Vdc pin were used for the dual paddle controllers that could be 
plugged into either port allowing a maximum of 4 players.  Hence the computer had four built in D to A converters.  I 
believe that the last pin was used for the light pen.

It had an I/O port for daisy chaining a tape drive, printer, plotter, or modem (1200 baud max I believe), and up to eight 
5.25 inch disk drives.  Built into the console was a cartage port, which again was on all Atari 8-bit computers.  This was 
the form of media that the game system developed all its games for.

The game system/computer had built in Atari BASIC.

My background with the computer:
The first PC I ever used was an Atari 800 computer that my school got in the 4th grade.  I loved it and so my parents bought 
me an Atari 800XL computer, Atari 1050 disk drive, and NEC monitor.  Overtime the chip that handled color on the computer 
stopped displaying green and so I sold the computer and bought a used XE game system to replace it.

I still own the computer and know a lot more information about it if you have any specific questiions.

Dave Di Giorgio
Ride Control Systems Project Engineer
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