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71

DOOM itself doesn’t do anything special to benefit from PCI graphics cards. It runs faster with PCI graphics cards (and VLB, AGP, and PCI Express cards) than with ISA graphics cards because the supporting bus is faster, so reads from and writes to video memory take less time. PCI goes to great lengths to preserve backwards compatibility with ISA-based VGA, ...


47

The manual says that the smallest resolution it can handle is 800x600. That is almost certainly the key. Original VGA supported 640x480 16-colors and 720x400 (essentially a small step up from the 720x350 monochrome (MDA) text, but with color). While VGA has come to mean "any video card and monitor that uses a blue 15-pin connector" that's not what ...


32

Seems like VGA only has one background layer, it appears to be a typical bitmap screen like most home computers of the 80s (Amstrad CPC, Commodore 64 etc.) where each pixel's color is stored in a section of memory that can be written to directly. Most video cards of the day could theoretically have up to four pages of video memory, as they had 256 KiB of ...


30

(When selecting an answer, use Stephen's - I just put this here because it is too much text for a comment) Most Important: It's a Game of Raw Numbers. We can ignore more complicated stuff and simply go for bandwidth: ISA had at the time a bandwidth around 16 MiB/s (*2) VLB (*1) and PCI offered up to 133 MiB/s bandwidth. A 320 x 200 screen needs 64 kB (...


22

DOS is almost surely not outputting 800x600 or up, and is probably in the ballpark of 720x350 or thereabouts. Further, it's likely 70Hz, which this adapter may not like. I'd recommend you get a display that can use the signal from card natively -- any old multiscan CRT and lots of early LCDs can do this -- but if you're determined to use this adapter, you ...


15

What was the phosphor resolution? The usual specification quoted for CRT resolution is the 'dot pitch', or distance between groups of RGB phosphor dots. Here are some examples of IBM monitors produced from 1987 to 1993 (taken from here):- Model Year Standard size viewable pixels dot pitch (mm) notes 8513 1987 VGA 12" 10.4" 640x480 ...


14

Running your code as-is on a real 286/VGA (Cirrus Logic CL-GD5420) produces this image: Inserting one dummy read before the second fill cycle (just mov ax, es:[0]) gives the image you were expecting: So it would seem that at least there might be a difference between the DOSBox implementation and the real hardware. If it does implement logic operations, ...


10

The 16-color modes on the VGA use a hardware design borrowed from the EGA. On the EGA (and VGA), the bitwise drawing modes don't act upon memory directly, but instead act upon values stored in four eight-bit registers, each of which holds a byte of data from one of four color planes. Reading any byte of data from the display will load each of the four ...


10

Is it on its own plane somehow? No, as you assumed, VGA has only one plane(*1). Is every letter a "mouse cursor?" Or, is the screen constantly being redrawn with the letters in their new position? The latter. Most likely it's composed of a background image moved into the frame buffer, overlaid by the text layer. (*2) The movement of the text is ...


8

Geenimetsuri's answer about colour cycling is a very good point that deserves a demonstration. :) Here's a GIF taken from the end of the first level of Episode 1 of Jazz Jackrabbit. I've slowed it down so you can see the layers. (Jazz runs at 60Hz and is famous for its speed!) Jazz Jackrabbit uses Mode X for the main gameplay screen. Mode X is a 256 colour ...


8

In the following I'm assuming you don't have the manual brightness control turned down to the minimum. That is the only trivial problem that might cause the issue. When the CRT isn't even able to display it's own OSD, there must be something seriously wrong with it. The OSD is produced by the CRT itself and should come up even without a working connection to ...


7

The main specifications indicate that the ZR24w only supports 60 Hz signals (59.9 – 60.1 Hz) and "text mode" is listed as 640×480. However, in the list of recognized modes in the monitor's manual (p. 37) all the modes are 60 Hz except for: Preset Pixel Format Horz Freq (kHz) Vert Freq (Hz) 2 720 × 400 31.469 70.087 Given the conflicting ...


7

The standard text mode for VGA DOS was 80 by 25 characters, which translated to a resolution of 720 by 400 (characters of 9 by 16 pixels) per the table on VGA text mode page in Wikipedia. One option would be to change the mode and see if you can get the resolution high enough for your converter, but that would depend on the capabilities of the graphics ...


4

1a. Yes, the shadow mask should be at least double the monitor resolution in both X and Y directions to give a good picture. 1b. Most monitors had hole-style (shadow) masks, but Triniton used an aperture grille with slots and wires that extended the entire vertical height of the image, with one or two wires running horizontally across the screen to stabilize ...


4

I've just realized I have a gap in my understanding of the VGA CRT monitors of the 80386 era (1980s-1990s). It may be more a general need to consult basic information about basic analogue TV/composite video signal structure, independent of PCs or time. What was the phosphor resolution? There is no general (practical) phosphor resolution. Resolution is an ...


3

RGBI to RGB only needs a couple of diodes and resistors, see e.g. here, and that will work with VGA-RGB. I am not aware off-the-shelf ones for that are available, OTOH they are not exactly difficult to make yourself. I have no idea what @mnem means by "RGBA", usually this is an abbreviation for red-green-blue-alpha, and refers to how image data is ...


3

Let me try a summary how analog CRT monitors work(ed). Let's start with monochrome, later explain the color models, and then answer your questions. How it works The CRT produces a thin electron beam that produces light when it hits the phosphor. A deflection circuitry can bend that beam so that it can reach all of the sreen front area. This circuitry is ...


3

The movement of the text is so smooth it appears to be hardware scrolling like you would see on the NES or Super Nintendo but as far as I'm aware MS-DOS PCs don't have that. To add a bit on the above excellent answers and comments... You had several other tricks you could employ on a PC to "emulate" smooth scrolling. First one, and very widely ...


2

An EGA or VGA game that used 16-color graphics mode could exploit those cards' bit-planar architecture to create either a 7-color foreground and 2-color background, a 3-color foreground and 4-color background, or 1-color foreground and 8-color background, without having to do any save/restore operations on the background. I don't know to what extend games ...


2

I can't recall the technical specifics after all this time, but I do remember that my ISA SVGA card (Trident 8900-based) would default to 8-bit bus traffic and 8-bit video-BIOS access. Getting both to 16-bit took quite some BIOS, TSR, and boot-time utility twiddling. Games were noticeably faster in fully 16-bit mode! So I doubt many ISA cards were actually ...


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