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Don't remember (and can't be arsed to check) if it was int21, but IBM PC BIOS does have a call to write text to the (B8000, usually) screen text buffer, complete with scrolling.

I do remember (and don't have to check [1]) but MS-DOS used interrupts 20h through 2Fh (mostly 21h). BIOS used interrupts 10h through 1Fh. 10h was for text and graphics. The "text" screen could be at either B000:0000 (physical address B0000) or B800:0000 (physical address B8000) depending on if it was monochrome or color, so to be pedantic, one had to make a few checks to see what card was installed (if you wanted to bypass the BIOS).

[1] Why do I even remember this stuff? I haven't used any of this since the early 90s! Sheesh!

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