What is the actual pixel resolution in standard DOS text mode? \ VOGONS

What is the actual pixel resolution in standard DOS text mode?

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First post, by videogamer555

Posted on 2017-05-01, 08:56

videogamer555 Offline

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I thought in 80x25 (80 character by 25 character) text mode, it was supposed to have a pixel resolution of 640x400 (and it appears to be so in DOS Box). However when running DOS in Oracle VirtualBox (when booting to a MSDOS 6.22 floppy disk image), and I measured the width and height of a screencap of the virtual machine's screen window, it appears to be 720x400. And if you look closely, the spacing between typed characters in VirtualBox is a bit wider than the spacing in DOSBox (though the size of the characters themselves is the same). Here's a picture that shows cropped sections of screenshots from each PC emulator (DOSBox and VirtualBox), showing the character spacing.

Which more closely resembles the behavior of real hardware?

Reply 1 of 5, by Scali

Posted on 2017-05-01, 09:10

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720x400 is right, for VGA.
The characters are 9x16 pixels each, resulting in (80*9)x(16*25) = 720x400 resolution.
MDA/Hercules is 720x350, EGA is 640x350, and CGA is 640x200 (respectively 9x14, 8x14 and 8x8 fonts).

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Reply 2 of 5, by Jepael

Posted on 2017-05-01, 19:32

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videogamer555 wrote:

Which more closely resembles the behavior of real hardware?

VirtualBox is right.

This is also a known feature of DosBox. It may not matter much as there's not that many text mode games, let alone text mode games that this would present a horrible graphics issue.

Any way, if the screens are 640x400 or 720x400 pixels, then when they are viewed on a modern display with square pixels, they both have incorrect aspect ratio, as the image should be viewed on a 4:3 aspect ratio where the pixels are not squares.

Reply 3 of 5, by Scali

Posted on 2017-05-01, 20:00

Scali Offline

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Jepael wrote:
Any way, if the screens are 640x400 or 720x400 pixels, then when they are viewed on a modern display with square pixels, they both have incorrect aspect ratio, as the image should be viewed on a 4:3 aspect ratio where the pixels are not squares.

Is that still relevant though?
I have a 4k monitor, and 1:1 pixel mapping is the last thing I want from an emulator. Those old resolutions of 320x200 and 640x480 are REALLY small on my display, so I want to stretch them by a significant amount anyway. Might as well perform some aspect correction while I'm at it.

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