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121 votes
Accepted

What character is the MS-DOS cursor?

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 ...
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93 votes
Accepted

Why do PCs boot in 720x400 resolution?

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 ...
  • 1,455
81 votes

Why were CLIs typically light text on dark background, whereas GUIs typically use(d) dark text on light background?

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, ...
  • 178k
72 votes
Accepted

How did old MS-DOS games utilize various graphic cards?

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 ...
  • 5,667
67 votes
Accepted

Reason for the Amiga clock speed

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 ...
63 votes

Why didn't early color TV sets accept RGB input?

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 ...
  • 1,397
60 votes

Why were some early PC 3D cards unsuitable for 2D graphics?

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 ...
  • 98.3k
60 votes

Why did the VIC-20 and C64 have only 22 and 40 columns when the earlier PET had 80 column text?

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 ...
  • 5,667
56 votes
Accepted

What determines the color of every 8th pixel on the Apple II?

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 ...
  • 178k
54 votes

What character is the MS-DOS cursor?

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 ...
  • 29.8k
50 votes

In the classic "Windows 98 crashes live on CNN" video, why does the BSOD appear so oddly?

VGA graphics and text modes have different scan rates. The Windows desktop runs in some graphics mode (looks like 640x480, likely 60 Hz) while the BSoD is in text mode (720x400 at 70 Hz). The adapter ...
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39 votes
Accepted

What mid-1970s to mid-1980s home computers had their graphics characters added to Unicode 13?

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 ...
  • 2,701
38 votes
Accepted

Commodore 64 to modern TV

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 ...
38 votes
Accepted

How did the Sega CD decompress video?

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 ...
37 votes

Why did some video games apparently use "interlaced" video modes?

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 ...
  • 20.3k
35 votes

Why did computer video outputs go from digital to analog, then back to digital?

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 ...
  • 57.8k
30 votes

Why did the VIC-20 and C64 have only 22 and 40 columns when the earlier PET had 80 column text?

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 ...
30 votes

How were the special effects achieved for the Kraftwerk Die Roboter 1978 music video?

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 ...
  • 178k
29 votes
Accepted

What are the differences between a PAL and NTSC C64?

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. ...
  • 8,452
29 votes
Accepted

How did the Amiga DCTV work

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'...
  • 3,612
29 votes
Accepted

Graphics chips in 1980

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 ...
  • 4,416
28 votes

How did old MS-DOS games utilize various graphic cards?

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 ...
28 votes
Accepted

Why did the TRS-80 CPU have priority over the display?

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 ...
  • 178k
27 votes

Is it possible to swap the Apple IIc's monochrome CRT tube for a color one?

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 ...
  • 295
23 votes

What graphical effects can be created by changing the VIC-II settings?

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 ...
  • 35.3k
23 votes

Why were CLIs typically light text on dark background, whereas GUIs typically use(d) dark text on light background?

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 ...
23 votes

Why did computer video outputs go from digital to analog, then back to digital?

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 ...
  • 20.3k
23 votes
Accepted

How were the special effects achieved for the Kraftwerk Die Roboter 1978 music video?

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 ...
22 votes

Reason for the Amiga clock speed

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 ...
  • 29.8k
22 votes
Accepted

Visible resolution of C64 video output, including borders

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. ...
  • 35.3k

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