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by bpeebles 75 days ago
To be more exact (in an excessive way), it uses the BIOS's code to set the video mode (INT 10h) which is probably a few dozen bytes (at least?) although I have been remiss at not ever reading them. And it depends on DOS configuring the memory space to leave an INT 20h call (to terminate the program) at a place that's easy to RET to. But, yeah, very little extra. But I'm not being negative at all and this is pretty nice code and on the impressive side of 256 byte demos from the 80s and 90s (and onward).
4 comments
aidenn0 75 days ago
Yes, this is very minimal; if it were self-booting the INT 20h call wouldn't be needed, but there's no getting around the INT 10h, unless you specialize for very specific hardware.

The entire 5150 BIOS fit in 8k, so even if it were laden with BIOS calls (which it's not) then that would be an upper-bound.

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userbinator 74 days ago
The VBIOS is around 32-64k. The modesetting path is probably a few k.

And it depends on DOS configuring the memory space to leave an INT 20h call (to terminate the program) at a place that's easy to RET to.

This has always been the case, and actually inherited from CP/M.

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rob74 74 days ago
Also, MIDI - I'm not very familiar with demo programming, but I guess using MIDI saves a lot of bytes compared to trying to do something similar with only the PC speaker?
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xnorswap 74 days ago
MIDI is a protocol for describing audio.

Sure, it saves a lot of bytes compared to PCM encoded wave-form data, but it's not really cheating anything unless we also consider the red, blue and green parts of the computer monitor to be cheating because we're not outputting colours as raw wavelengths, but instead the monitor is decoding compressed signals into actual colours.

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rob74 74 days ago
What is this "cheating" you speak of? I wasn't expressing any judgement, just saying that using MIDI helps save bytes. But now that you mention it, the bitmapped graphics that we take for granted nowadays also help (it gives you a whole memory space to work with that doesn't count towards the length of your program, rather than having to "race the beam" -https://en.wikipedia.org/wiki/Racing_the_Beam). Not sure if there's a demoscene for the Atari 2600, but that would probably be the most "bare-metal" you could get...
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userbinator 73 days ago
Not sure if there's a demoscene for the Atari 2600

Of course: https://www.pouet.net/prodlist.php?platform%5B%5D=Atari+VCS&...

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HellMood 74 days ago
Thanks :)

and yes, your observations are spot on.

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