From the readme:

> that uses the BIOS to load data from the boot disk

That's not a bootsector demo (it's larger than 512 bytes). From reading the source: It's a hybrid bootloader + demo, in a pragmatic manner.

Here's an eclectic selection of other nice, not widely known christmas themed demos I found earlier (merry christmas!):

https://www.youtube.com/watch?v=6X74bhXltFo (BBC Micro)

> Bitshifters - Xmas 19 Demo

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https://www.youtube.com/watch?v=1t02TvLbQec (PC, CGA)

> Una simpatica demo natalizia datata 1986 per l'amato PC. Quante volte l'ho guardata quand'ero più giovincello:o)

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https://www.youtube.com/watch?v=hDitgPGh_MQ (Atari 8-bit)

> christmas collection demo for Atari 8-bit