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Anyone that's seen an Atari 400/800 next to a VIC-20 or C64 will know what I'm talking about - the Atari display was much, much sharper. It had a similar advantage over the Apple II, and I seem to recall the CoCo being somewhere between the Atari and C64's.

Does anyone know why? I suspect it might have something to do with all the shielding, which would imply later models in the XL series would lose some of the sharpness, but I did not use those machines either.

  • As here? youtube.com/watch?v=UNf8OQaud2M&t=7m51s That's exactly the same quality the C64 reaches on a TV set. If you wanted better quality, you had to connect a good monitor to both. – Janka Dec 21 '18 at 22:55
  • I have no idea what's going on in that video, but I assure you the normal output of the machines was dramatically better than shown. Dramatically. And that is a monitor. – Maury Markowitz Dec 23 '18 at 0:27
  • The video output of a C64 on a monitor is also not that bad. Not even with composite. The TV modulators Commodore used are crap, yes. – Janka Dec 23 '18 at 0:29
  • This is very interesting. In Germany the "Stiftung Warentest" (an organization testing products of any kind) tested home computers in 1984. The computers tested were: C64, TI-99, 600XL, CoCo, Dragon 32, Spectrum, Color Geny. (PAL versions, not NTSC) Their result was that only C64, Spectrum and TI-99 had a "good" picture on the TV set. 600XL was the only machine with the result "bad picture". – Martin Rosenau Dec 23 '18 at 9:42
  • Well that's why I added the comment about the XLs, these were cost-reduced machines so I'm not surprised if the video was not the same quality. – Maury Markowitz Dec 23 '18 at 16:50
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Why did the Atari's have such clear displays?

I suspect it might have something to do with all the shielding

No. As usual it's about the effort the designers did put into the display. To reduce cost, the VIC-II outputs an already internally mixed B&W signal and chroma. While this is basically like S-Video, the quality is defined by the internal generator - and doing analogue on a primary digital process is always a challenging task - especially if one want's to save money like Commodore did. In addition the external circuit is rather frugal.

In contrast the Atari's CTIA/GTIA output is fully digital and gets further 'sharpened' by a 4050 CMOS inverting buffer. Thus these signals are already way more 'clean' before geting mixed in a somewhat more elaborate diskrete analogue section. Here is a nice page showing the circuitry in detail for the purpose of an easy modification to get an S-Video compatible output.

Also the modulator used, at least for the 800 is of a better quality than the one for the C64 - but that's only relevant for TV, which is less than desirable anyway - still, here the Atari outperforms the Commodore as well.

I guess it pays out that Atari designers had quite some experience with TV/colour when creating the 400/800 output circuit.

  • Honestly, the only major difference I can make out is the resistor ladder for the luma not being present in the VIC-II schematic. That makes total sense as the VIC does only employ four levels of luminance – black, dark, light and white. I can't see how this affects signal sharpness. – Janka Dec 22 '18 at 2:17
  • A fine answer as always Raff. I can't speak to the internal signal because I only ever used it on a TV. The Atari's TV output was basically the equivalent quality of the C64 on a 1701. I wonder if that's the reason Atari never released their own monitor, simply that it didn't make enough of a difference? I saw an 800 on a monitor, and it was better, but not a lot better. – Maury Markowitz Dec 23 '18 at 0:26
  • Oh yeah, were you ever able to grab pix of the Sol-20 expansion bus? – Maury Markowitz Dec 23 '18 at 0:31
  • Yes. I totally forgot about them. sorry. Let me search and send them. ok? – Raffzahn Dec 23 '18 at 0:46
  • @MauryMarkowitz Looking at the signal with a scope will show the quite obvious difference. Fro the mintor I guess Atari always thought of home consumers using a TV as their main target market. – Raffzahn Dec 23 '18 at 0:48

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