I had a 386 PC with 4MB of RAM when I was a kid, and it ran Windows 3.1 with a GUI, but that also had a VGA display at 640x480, and only 16-bit color (4 bits per pixel). So 153,600 bytes for the frame buffer.
The "high color" (16 bit) mode was 5:6:5 bits per channel, so 16 bits per pixel.
> So 153,600 bytes for the frame buffer.
And so you're looking at 614.4 KB (600 KiB) instead.
To be frank, I wasn't aware such a mode was a thing, but it makes sense.