One of the Hugi-compo rounds was a Pong game http://www.hugi.scene.org/compo/compoold.htm#compo3 to be run under MS-DOS; the winner was 142 bytes. However, there were several smaller entries that were disqualified for some cosmetic or lifecycle problems that didn't affect playability, the smallest of which was 67 bytes. The rules specified things including the paddle width, the text mode, the color of the ball, the win text, and the keys used to control the paddles. It seems likely that a smaller playable Pong could be achieved by relaxing the rules further — for example, by using different keys to control the paddles, or using a different starting ball position.

A boot sector doesn't have the MS-DOS interrupt services; it has to use only the BIOS interrupt services. On the other hand, it doesn't have to worry about exiting cleanly and resetting the video mode either :)

The winning entry, by Guillermo Sais, was:

    0000000: b003 cd10 95fa bea2 00b3 a068 00b8 07bf  ...........h....
    0000010: 6401 8d70 028d 02f6 75a6 80fc 0477 03f6  d..p....u....w..
    0000020: 5db0 d419 7520 287d d795 cd10 b409 ba34  ]...u (}.......4
    0000030: 01cd 21c3 506c 6179 6572 2031 2068 6173  ..!.Player 1 has
    0000040: 2077 6f6e 2e24 e460 a881 7813 7501 afd4   won.$.`..x.u...
    0000050: 05b0 f674 02b0 0a02 053c 8c77 0288 05b8  ...t.....<.w....
    0000060: db0a 99b2 00bf 000f b114 ab87 d7e2 fb26  ...............&
    0000070: 8134 fc0e 487a 9826 3800 7602 f7db b14f  .4..Hz.&8.v....O
    0000080: bada 03ec 33c1 2408 7bf9 e2f7 ebd4       ....3.$.{.....