The 350-line modes are a bit of a special on VGA systems, they are actually delivered with the exact same timings as the 400-line modes, but with a total of extra 50 lines of padding added at the top and bottom. The last one at 60 Hz vertical refresh, the others at 70 Hz. A VGA monitor cannot display a 320x200 mode, the display controller uses double-scanning and pixel doubling to send two lines and/or pixels to the monitor so that a 320x200 resolution, 640x200 resolution, and (if one goes beyond BIOS) 320x400 resolution are all actually displayed as 640x400. There are 17 modes listed in that table, but that is an illusion. The 25.175 MHz clock was used for 640-wide modes, the 28.322 MHz clock for 720-wide modes. The VGA chip itself had whopping two pixel clock rates (25.175 MHz and 28.322 MHz), nothing programmable like mid-1990s cards (when you look at old graphics cards like this one, they usually have two to four discrete oscillators on them, very low-tech). If you look at the second table here and just consider the VGA graphics modes 0 to 13h, you'll see that the original VGA monitors were dumb fixed-frequency monitors with 31.778 KHz horizontal refresh, no fancy multisync. Note that VGA text modes also had higher refresh rate (70 Hz) than 640x480 graphics modes (60 Hz). At 400 pixels high, you still get 25 lines of 16 pixel high character cells, which was entirely sufficient. The reasons were probably ergonomic more than anything, the extended 9 pixel wide character cells are more legible than 8 pixel wide, but the cards had limited pixel clocks and monitors had fixed horizontal frequency, so the added horizontal resolution came at the expense of reduced vertical resolution. But VGA text modes were never 640x480 (except, one way or another, on laptops with a 640x480 LCD) and by default used 720x400 resolution, same as the old MDA (monochrome text-only cards). That was the highest-resolution graphics mode which all VGA chips (and monitors) could handle. The so-called "VGA" resolution is 640x480. Dec 2007, 15:45 Primary OS: MS Windows 7 VBox Version: PUEL Guest OSses: Any and all michaln Oracle Corporation Posts: 2976 Joined: 19. That will rescale the screen contents to a fixed window size rather than the other way around. The closest you can get to the "right" aspect ratio is probably running the VM in scale mode (Host+C). The GRAFTABL command is used to load fonts supporting alternative codepages.īut that's not very relevant, because although GRAFTABL can load different character glyphs, it cannot change the size of the character cells, that's defined by hardware. DOS is perfectly capable of overriding those, and it is a requirement for supporting any "international" codepages, as the BIOS fonts only support the standard IBM codepage 437. VirtualBox (VGA BIOS) does supply its own "hardware" fonts, and the fonts VirtualBox uses match standard IBM fonts. The does indeed result in the "wrong" aspect ratio because the pixels on a classic VGA monitor wouldn't be square, but in a VM they are. The normal resolution of a 80x25 text mode is not 640x480, it is 720x400 because the character cells are 16x9 pixels wide.
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