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81

Why did early CLIs seemingly so predominantly use light on dark color schemes, and what drove the shift to GUIs using dark on light color schemes instead? Simple: CRT technology (and, as so often, missing the need to do otherwise) Early CRT technology was not able to deliver black on white. Further it was more important to make a readable display early on, ...


66

Did every programmer of every game implemented all possible various API's that old graphic cards supported? Yes - but it went even deeper than that. Early graphics cards had virtually no callable code associated with them at all, the concept of "drivers" had not quite become a reality yet. There was the concept of a Video BIOS, which were extensions to the ...


65

The architecture of most "color computers" of the 70s-80s was very tightly built around the NTSC color video standard. Almost all of them had a 14.31818 MHz crystal. Note that this is four times the 3.579545 MHz frequency of the NTSC color standard, which was called a "color clock". They divided that crystal frequency to derive their actual clock ...


52

A nice one - and coming up every now or then. TL;DR The Apple IIs video logic produces a B&W bitstream at the right frequency to bedazzle an NTSC TV set in a way to make it 'see' colour. The colours produced are based on the way the bitstream creates interferences that are detected by the TV set as colour information. The encoding is rather a series ...


35

The VIC-II chip inside the C64 computer outputs a S-Video signal, which is mixed and modulated into the matal box that contains the UHF modulator circuit. Earlier models made composite video available on the A/V DIN connector. Later models also made separate componentes (luminance and chrominance) available as well. For the sake of image quality, and as you ...


33

Early digital video outputs, like CGA, were not really akin to the later standards such as DVI and its follow-on's. The reason for using multiple lines to carry the different analog portions of the signal to the monitor was to prevent crosstalk interference of these signals. You can see this in the very early computers like the Commodore 64 and Atari 800 ...


28

Hardware-wise, the Commodore 64, like most early computers, was synchronized to its graphics output: in the case of the C64, the CPU clock was derived from the timing crystal in the video hardware. From a game-programming standpoint, the most important timing element is the vertical refresh rate: the 50 Hz (PAL) or 60 Hz (NTSC) rate at which the screen ...


28

There were. A couple of examples are the Motorola MC6845 and the MC6847. These chips were flexible and allowed various resolutions and colors depending on how they were implemented. The MC6845 was used in the Acorn BBC Micro, the Amstrad CPC and the IBM PC MDA and CGA video adapters. The MC6847 was used in the Tandy TRS-80 [Model 1], the Acorn Atom, the ...


26

After some research, I found the hardware engineer that built the DCTV and we exchanged some messages where he explained the system. This is the unedited text: Wow, it has been a long time... I didn't really remember! Luckily I still have all the lab books and design notes from those days filed away. We used a technique that encoded the data on two ...


26

Early on, you had to explicitly code your game for each graphics card you wanted to support: Hercules, CGA, Tandy, EGA, VGA. You had to know how to put the card into graphics mode and you had to know the memory layout, palette, and so on. You had to figure out how to avoid flicker and how to prevent tearing. You had to write your own line drawing and fill ...


23

From the Macintosh Folklore Site: The Apple II displayed white text on a black background. I [Bill Atkinson] argued that to do graphics properly we had to switch to a white background like paper. It works fine to invert text when printing, but it would not work for a photo to be printed in negative. The Lisa hardware team complained the screen ...


21

In the UK in the 1980s and the early 1990s, no video input at all was common. Early video recorders and set top boxes (for the new digital channels) would use RF out. You would disconnect the aerial from the TV, connect it to the VCR or STB, and connect the VCR or STB to the TV with another aerial cable. The TV would see it as an extra channel. You might ...


21

Before VGA was invented, CGA RGBI used 4 wires to get 16 colors and EGA used 6 wires to get 64 colors on the cable. Add 3 more for sync signals and signal ground, and this won't be an issue, simple cables and connectors exist for getting EGA's about 16.3 million pixels per second digital signals over to the monitor easily. Amiga was released. It supports 4 ...


20

When color video was introduced in the USA, the horizontal scan rate was set as precisely 15750 * (1000/1001)Hz, i.e. roughly 3579545.4545Hz and the color sub-carrier frequency (also called the chroma clock) was defined as 227.5 times the horizontal scan rate. Many computers of that era use a multiple of the chroma clock as the pixel clock (the Amiga, for ...


20

It's unclear what you mean by "visible", since that's a feature of your monitor, not of the computer. That's because there's a fairly huge area which is not intended to be displayed, but could be. That's called the overscan area, and since that varies widely from TV to TV, that's why the home computers all had this border. But the Commodore 64 has 63 to 65 ...


19

Most classic computers will work fine on a TV with proper composite inputs. You want to make sure your TV has aspect ratio selection as many simply horizontally stretch the 4:3 image to 16:9. As for Atari's, it will depend on which model you have and what cabling you have. I've very successfully run Atari 800XL and 1200XL systems with LCD TVs using the ...


19

S-Video relies on colour transformation from RGB to YUV, and then takes the U and V and modulates them using a colour subcarrier. The TV has to undo all these steps in order to get the original RGB signal. If the subcarrier frequency is not in phase with the pixel clock (as will be the case if using different crystals), then moving artifacts will show up in ...


19

Up until ~1980 the only connectors TV sets had were Belling-Lee type antenna in. So most VCR and next to all home computers did use RF modulated output toward the TV set (*1). This included even cable networks. While Type F connectors where used for more sophisticated equipment, households were still fitted with Belling-Lee. Professional equipment of the ...


16

The VIC-II has many settings that can be changed, and also has the ability to produce an interrupt whenever a particular scanline has been hit. This allows us to make for example: horizontal scanlines set an interrupt when the electron beam reaches a particular scanline. Change the border color when the interrupt happens, and then set another interrupt a ...


16

There are 63 to 65 clock cycles in a scanline, depending on the VIC model (PAL, old/new NTSC). Each cycle consists of two phases, the 6510 is only able to access memory in the high phase, the VIC-II can access it in both phases. So, a PAL VIC-II can read 63 bytes from memory, without disturbing the processor at all. Sprite color and coordinates are stored ...


16

I designed a color graphics card for the Z80 ECB bus back in 1984 or so, based on the 6845. The 6845 was "just" a timing and addressing generator. It was meant for character-based displays. So it divided the display area in character cells. Each character cell could span some horizontal pixels (to be serialized outside of the 6845) and some vertical scan ...


16

In DOS you had direct access to the hardware; so you grabbed some good source of information about the card you wanted to support, and got down to code your routines. A book which was often cited as a good source was "Programmer's Guide to the Ega, Vga, and Super Vga Cards", by Richard F. Ferraro; I hadn't the luck to own it or read it, but it was fondly ...


15

Before SCART, European TVs often had not video input at all or S-Video on 6-pin or 8-pin DIN sockets (not Mini-DIN). Cinch composite was uncommon until VCRs came out. After that the old S-Video connectors died out and it was most common for cheap TV sets to have only an antenna and one composite in, better TV sets had a SCART input very early. Component ...


15

A lot of the time the answer is "not without difficulty": chips from 6502 machines tend to simply assume they have access to the bus every other cycle; you can't achieve that on a Z80 without stopping the clock every other cycle which would be hugely wasteful since memory accesses are only as-required. The Z80 devices tend to fiddle with the clock and/or use ...


15

Since nearly all early computers used TV quality CRT screens, they suffered from phosphor burn in so the more you limited visible areas the longer your CRT would last. More expensive higher quality monitors had less of a problem but the price tag did not appeal to the mass market. The early TV quality monitors had pronounced flicker and many video card ...


15

I won't get into details of why white on black, as others have explained that this mostly due to limitations of CRT technology at the time. One of the main reasons for the switch to black on white in GUIs, though, is skeuomorphism: GUIs (especially the early ones) tried very hard to emulate real-life, and have lots of things like folders, trash bins, and ...


14

This may answer your question. This is my setup: a ZX Spectrum 48K and a 1084 CRT monitor. The Spectrum has been modded to output a composite signal instead of RF. And this is a close-up on the picture the monitor shows: So yes, the Spectrum generated scanlines, but this effect depends largely on the TV set used. My memories are also of a completely pure ...


14

I think you meant 7.15909 MHz. 7.15909 MHz is twice the NTSC color burst frequency (3.579545 MHz). The NTSC color burst frequency is 455/2 times the line rate, the line rate is 262.5 times the field rate, and the field rate is 60 * 1000 / 1001 (59.94 Hz). See also https://www.repairfaq.org/samnew/tvfaq/tvwinsswf.htm On PAL systems that have different ...


14

The Motorola MC6847, used in the TRS-80 Color Computer, or the Texas Instruments TMS9918 would be good candidates. Both were available in 1980, and could display 256x192 pixel colour images.


14

This is just the well-known "AEC Glitch" of the C64's video output, exacerbated by the additional analog distortion of the RF output to a TV. Anyone who used a C64 on any kind of display is familiar with the vertical stripes that appear. This is caused by interference leaking into the Luma (aka Luminance, or Intensity) portion of the video output. The ...


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