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119

The text-mode cursor isn’t a character, it’s managed separately by the video output circuitry (which is how it keeps blinking even when your computer is busy or locked up). It can be enabled or disabled, and its size can be determined — at least, its start and end scanlines, which determine its height; the cursor always occupies the full width of a character ...


93

This is historically not uncommon at all. Before starting an Operating System and initializing a graphics mode, your PC operates in the simplest display mode available, 80×25 text mode. The original VGA 80 × 25 text mode (that is still supported by most modern graphics cards) has characters with a resolution of 9×16 pixels per character. This adds up to 80×9 ...


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, ...


70

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 ...


67

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 ...


63

When colour television broadcasts began (1960s, in the UK; perhaps a little earlier in North America?) there weren't any local devices that customers might want to use. Broadcast TV was the only source of images that any home user could imagine. Adding extra circuitry to handle separated R, G, B and sync inputs (with appropriate protections against overload ...


60

Early high-performance 3D accelerators such as the Voodoo Graphics have limited framebuffer resolutions (640×480 for most Voodoo Graphics configurations, 800×600 for the Voodoo2 in non-SLI) and colour depths (16-bit with dithering), which make them unsuitable for 2D — in the second half of the nineties, 1024×768 was a requirement at least in computer ...


56

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 of ...


53

The cursor on the CGA, MDA, EGA, and VGA cards was a hardware sprite generated on the earlier cards by the 6845 video controller, and on later cards by a chip that emulates the 6845. That chip has an address counter that is used to fetch data from memory, as well as a line counter and a cursor-state latch. It also has a programmable registers for cursor ...


52

One reason was likely that the VIC-20 and C64 did not have their own displays, but were designed to be connected to a television set. The interface between the computer and the television was not sufficient to display 80 column text (it would have been almost unreadable). However, the PET had its own integrated display so it did not have this limitation, and ...


39

The new additions mentioned are mostly to be found in the new Symbols for Legacy Computing block (PDF link) covering the 1FB00–1FBFF codepoint range. This block includes: a large number of BLOCK SEXTANT characters like 🬥 BLOCK SEXTANT-1236 ("The term 'sextant' refers to block mosaics divided into six parts." Also note because these definitions are new, ...


38

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 ...


37

We used to have to write our own video playback system, so each game did it differently. I worked on Microcosm for the SegaCD and if I recall we used a 16 colour palette for the video playback and had to create our own compression and decompression tools to keep the overall data bandwidth below 150KiB/sec. Later games used tricks like changing the palette ...


37

Indeed, early devices such as C64, NES, or IBM PC with CGA adapter did not use interlacing, but simply sent 240p to the TV. And later devices such as the Amiga could send either 480i or 240p. But TVs were not 480p capable, only 480i or 240p. So it was not possible to use 480p. For example, Amiga 500 can send either interlaced 480i for hi-res graphics and ...


35

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 ...


29

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 ...


29

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 ...


29

It may be helpful to note that this is not a live recording but a pre produced video. These are pretty standard analogue (post production) effects at the time. Including real mirrors, two cameras and insertions. The only digital effect here is the text. German TV, foremost progressive music shows, of the 1970s was notorious for using cutting edge technology. ...


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

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 ...


28

Why did they instead give the CPU priority? It's the lowest effort solution. It needs no additional hardware (*1). At the same time it's a transaction safe solution. Whatever the CPU writes gets written (or read). So no data loss. Letting the CPU wait would need some logic to extend a CPU access cycle. A countable effort even if 'only' a few TTL. For a ...


27

If you don't know, then the answer is "no". It certainly is possible to get a color CRT tube and matching electronics and fit them into a cleared out case. However, if you have to ask people on the internet, then I'm pretty sure that the responsible answer to give you is: Keep your hands off. CRT tubes are high voltage electronics. They are evacuated, i.e. ...


24

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 ...


23

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 ...


23

Use of TV as monitor is the reason for these low resolutions. The issue is that the color resolution of TV is very low. While B&W TV could resolve pixel small enough for ~400 to ~600 pixels, color resolution was much much lower, barely around 200 pixels. Some computers exploited this, such as Apple II and CGA/composite. It also shows the limits of that ...


23

All of these effects are being created using beam splitters to combine two images of the original recording. The lower resolution is a product of the second image, the lower in the horizontal split for instance, being viewed through a mirror and splitter. A single tape of the original recording is played on a studio monitor, with one side of the splitter ...


21

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 ...


21

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 ...


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

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 ...


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