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Why the original Macintosh had a screen resolution of 512×324

512pixels.net

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Re: Why the original Macintosh had a screen resolution of 512×324

#101

Post by krige »

analog31 wrote: post #42
pavon wrote: post #29

The article didn't nail down an exact reason. Here is my guess. The quote from Andy Hertzfeld suggests the limiting factor was the memory bandwidth not the memory volume: > The most important decision was admitting that the software would never fit into 64K of memory and going with a full 16-bit memory bus, requiring 16 RAM chips instead of 8. The extra memory bandwidth allowed him to double the display resolution, g…

A lot of those old machines had clock speeds and video pixel rates that meshed together. On some color machines the system clock was an integer multiple of the standard colorburst frequency. The Timex Sinclair did all of its computation during the blanking interval which is why it was so dog slow.

The Commodore Amigas had their 68k clock speed differ based on region due to carrier frequency difference (more specifically, 2x freq for NTSC, 1.6x for PAL, which resulted in almost the same, but not quite, clock speed).

It's interesting how the differing vertical resolutions between these two (200p /400i vs 256p /512i) also had some secondary effects on software design, it was always easy to tell if a game was made in NTSC regions or with global releases in mind because the bottom 20% of the screen was black in PAL.

Re: Why the original Macintosh had a screen resolution of 512×324

#102

Post by johnklos »

perching_aix wrote: post #19

Regardless of whether we go with 512x324, 512x342, or 512x384, the claim of 72 PPI (exact) and 9" of diagonal size (exact) are not simultaneously possible. Extremely nitpicky thing I know, but this kinda stuff really bugs me, could somebody please clarify what was the real size (and/or PPI) here? For reference: 512x324 @ 72 PPI = 8.42" (or 214 mm) (rounded) 512x342 @ 72 PPI = 8.55" (or 217 mm) (rounded) 512x384 @ 72…

A square that's one thousand units by one thousand units doesn't give a rational number, much less an integer one, for the diagonal.

A 9" CRT would never be precisely 9", because beam trace width and height are analog, plus there's overscan, so a 9" screen would simply give something pretty close to 9".

Re: Why the original Macintosh had a screen resolution of 512×324

#103

Post by ido »

analog31 wrote: post #42
pavon wrote: post #29

The article didn't nail down an exact reason. Here is my guess. The quote from Andy Hertzfeld suggests the limiting factor was the memory bandwidth not the memory volume: > The most important decision was admitting that the software would never fit into 64K of memory and going with a full 16-bit memory bus, requiring 16 RAM chips instead of 8. The extra memory bandwidth allowed him to double the display resolution, g…

A lot of those old machines had clock speeds and video pixel rates that meshed together. On some color machines the system clock was an integer multiple of the standard colorburst frequency. The Timex Sinclair did all of its computation during the blanking interval which is why it was so dog slow.

To save the curious a search: the Timex Sinclair is the American variant of the ZX Spectrum.

Re: Why the original Macintosh had a screen resolution of 512×324

#104

Post by fredoralive »

badc0ffee wrote: post #97

It doesn't say exactly why 512x342 was chosen. But I'm more interested in why it was changed to 512x384 on later Macs. Is it just to fill the full 4:3 screen? Beyond that, this article really wants to tell you how amazing that resolution was in 1984. Never mind that you could get an IBM XT clone with "budget" 720x348 monochrome Hercules graphics that year and earlier.

The 512x384 models are Macintosh LC adjacent, so the original LC monitor (the LC itself can do 640x480), or the Colour Classics. AFAIK it was partly in order to making the LC work better with the Apple IIe card (although the IIe software uses a 560x384 mode).

A Hercules card, whilst nice does suffer from the same non-square pixels issue as the Lisa, so not as nice for creating a GUI.

Re: Why the original Macintosh had a screen resolution of 512×324

#105

Post by nyanpasu64 »

kragen wrote: post #87
nyanpasu64 wrote: post #41

Earlier quoted context omitted.

- I hear that some later digital PAL TVs stored an image in a framebuffer and scanned it out twice at 100 Hz, which retro gamers today avoid because it increases latency relative to direct scanout. - I've heard mixed reports over whether CRT monitors had faster-decaying phosphors than televisions. Maybe part of it is a computer has a white image, which causes more noticeable flicker than a dark background with white…

I took film photos of my family's color TV in the 90s with a fast shutter speed. About 20% of the screen was fading at any given time with the (NTSC) 60Hz field rate, the rest being black, so to get a screen that was physically flicker-free with those phosphors, you'd have to refresh it at somewhere around 500Hz. I doubt color CRT monitors had faster-decaying phosphors than my color TV.

I looked up my brightness measurements of a Gateway VX720 VGA monitor (like Diamond Pro 710), and it seems the blue and green phosphors decay to 50% brightness in under 30 microseconds while red stays bright for 300 microseconds. I didn't measure how long it took for them to go to near-black levels. Sadly I never took measurements of my Trinitron TV when I still had it. All in all the results are inconclusive.

Re: Why the original Macintosh had a screen resolution of 512×324

#106

Post by msephton »

kragen wrote: post #90
perching_aix wrote: post #19

Regardless of whether we go with 512x324, 512x342, or 512x384, the claim of 72 PPI (exact) and 9" of diagonal size (exact) are not simultaneously possible. Extremely nitpicky thing I know, but this kinda stuff really bugs me, could somebody please clarify what was the real size (and/or PPI) here? For reference: 512x324 @ 72 PPI = 8.42" (or 214 mm) (rounded) 512x342 @ 72 PPI = 8.55" (or 217 mm) (rounded) 512x384 @ 72…

You're right, it's 8.55 inches at 512×324. There were black bars at the top and bottom.

And left and right, as the image was centred.

Re: Why the original Macintosh had a screen resolution of 512×324

#107

Post by msephton »

kragen wrote: post #82
nothercastle wrote: post #63

Earlier quoted context omitted.

Why did they need 60hz? Why not 50 like Europe? Is there some massive advantage to syncing with the ac frequency of the local power grid?

Conventional wisdom a few years after the Macintosh was that 50Hz was annoyingly flickery. Obviously this depends on your phosphors. Maybe it was already conventional wisdom at the time? I feel like the extra 16% of screen real estate would have been worth it.

Speaking of phosphors, early Photoshop had a setting to pick what you were using. These adjusted RGB balance according to published or measured values. https://twitter.com/gingerbeardman/status/154371808662010265...

Re: Why the original Macintosh had a screen resolution of 512×324

#108

Post by implements »

analog31 wrote: post #42
pavon wrote: post #29

The article didn't nail down an exact reason. Here is my guess. The quote from Andy Hertzfeld suggests the limiting factor was the memory bandwidth not the memory volume: > The most important decision was admitting that the software would never fit into 64K of memory and going with a full 16-bit memory bus, requiring 16 RAM chips instead of 8. The extra memory bandwidth allowed him to double the display resolution, g…

A lot of those old machines had clock speeds and video pixel rates that meshed together. On some color machines the system clock was an integer multiple of the standard colorburst frequency. The Timex Sinclair did all of its computation during the blanking interval which is why it was so dog slow.

There’s an interesting blog post about how a far simpler machine generates its video signal, if people are curious about the signals involved:

http://blog.tynemouthsoftware.co.uk/2023/10/how-the-zx80-gen...

“The CPU then only produces a TV picture when BASIC is waiting for input (or paused). At other times it does not bother to produce a video picture, so the CPU can run the program at full speed.”

Re: Why the original Macintosh had a screen resolution of 512×324

#109

Post by p_l »

hulitu wrote: post #99
stefan_ wrote: post #45

Earlier quoted context omitted.

Displays are still bandwidth killers today, we kept scaling them up with everything else. Today you might have a 4k 30bpp 144hz display and just keeping that fed takes 33Gbit/s purely for scanout, not even composing it.

And marketing said, when LCDs were pushing CRT out of the market, that you don't need to send the whole image to change a pixel on an LCD, you can change only that pixel.

except DVI is essentially VGA without Digital-to-Analog part, and original HDMI is DVI with encryption, some predefined "must have" timings, and extra data stuffed into empty spaces of blasting a signal designed for CRT.

I think partial refresh capability only came with some optional extensions to DisplayPort.

Re: Why the original Macintosh had a screen resolution of 512×324

#110

Post by p_l »

bane wrote: post #76

The answer is something that's harder and harder to do these days with all the layers of abstraction -- set a performance target and use arithmetic to arrive at the specifications that you hit and still achieve your performance goal. It's a bit of work, but I suspect you can arithmetic your way through the problem. Supposing they wanted 60 Hz on the display and a framebuffer you need 196,608 bits/24,576 bytes/24 kbyt…

Motorola 68000 used had 16 data lines and 24 address lines, so it took at least two cycles to just transfer a CPU full word (disregarding timings on address latches etc).

Some of the code AFAIK used fancy multi-register copies to increase cycle efficiency in graphics code.

As for screen, IIRC making it easy to correlate "what's on screen" and "what's on paper" was major part of what drove Mac to be nearly synonymous with DTP for years.

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