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

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

#111

Post by p_l »

tom_ wrote: post #15
nssnsjsjsjs wrote: post #12

Earlier quoted context omitted.

It was 32bit?!

The 68000 is 16 bit internally, and can access memory only 16 bits at a time, but the instruction set was designed with future iterations in mind, and most instructions can operate on 32 bit quantities - with a performance penalty. (Because in essence it has to do the work in 2 stages.) Whether this is enough to make it count as actually 32 bits is one for the philosophers.

It started out as 16bit enhancement to previous product, and evolved into being a 32bit architecture over development time.

The separation of Data and Address registers are also result of how it evolved over time, AFAIK, ultimately because it allowed to make the CPU cheaper/easier to make. Another element is that 68000 at least has two layers of microcode - first microcode engine generates instructions interpreted by second microcode engine which finally actually drives execution units.

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

#112

Post by p_l »

dtgriscom wrote: post #58

I remember in the early '80s using a computer (a Xerox Star, perhaps?) that used the CPU to generate the display. To speed up CPU-intensive tasks, you could blank the screen.

Alto had its entire display control in microcode, IIRC.

Out of similar tricks, Symbolics 3600 (at least first model) had major portions of disk driver implemented as one of the tasks in microcode (yes, the microcode was a multi-tasking system with preemption). Don't know how much of MFM wrangling was going there, but ultimately it meant that reading and writing a page from/to disk was done by means of single high level instruction

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

#113

Post by p_l »

pezezin wrote: post #98
perching_aix wrote: post #24

Earlier quoted context omitted.

It's always surprising for me to see people regard 60 Hz CRT as "flicker-free", or "minimal flicker", etc. Whenever I saw a CRT running at 60 Hz, I'd be immediately be able to tell. Always used at minimum 75 Hz but preferably 85 Hz at home (early 2000s, Windows).

I have recently been playing with CRTs again, and something that I have noticed is that for fast-paced games running at 60 or 70 Hz* I don't notice the flicker much, but for text anything less than 85 Hz is headache inducing. Luckily the monitor I got can do 1024x768 at 100 Hz :) * The original VGA and thus most MS-DOS games ran at 70 Hz.

I remember when I got my first computer for myself, instead of sharing with others, it was "obvious requirement" that the screen runs at least 72Hz, preferably higher. Which was why 15" CRT had to run at 800x600.

Later on, and with graphic card that had more than 2MB of RAM, I remember experimenting a lot with modelines to pull higher refresh rates and higher resolution on the 17" CRT I inherited when my father switched to a laptop :)

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

#114

Post by rwmj »

ido wrote: post #103
analog31 wrote: post #42

Earlier quoted context omitted.

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.

The ZX Spectrum had (primitive) video hardware. The GP commenter means the ZX80 and ZX81 which used the Z80 CPU to generate the display and so really were unable to both "think" and generate the display at the same time. On the ZX81 there were two modes, SLOW mode and FAST mode. In FAST mode the Z80 CPU prioritized computations over generating the display, so the display would go fuzzy grey while programs were running, then would reappear when the program ended or it was waiting for keyboard input.

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

#115

Post by ido »

rwmj wrote: post #114
ido wrote: post #103

Earlier quoted context omitted.

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

The ZX Spectrum had (primitive) video hardware. The GP commenter means the ZX80 and ZX81 which used the Z80 CPU to generate the display and so really were unable to both "think" and generate the display at the same time. On the ZX81 there were two modes, SLOW mode and FAST mode. In FAST mode the Z80 CPU prioritized computations over generating the display, so the display would go fuzzy grey while programs were runnin…

You're right! I was thinking of the Timex Sinclair 2068. It was preceded by the 1000 and 1500 (ZX80 & ZX81 respectively as you say).

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

#116

Post by implements »

rwmj wrote: post #114
ido wrote: post #103

Earlier quoted context omitted.

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

The ZX Spectrum had (primitive) video hardware. The GP commenter means the ZX80 and ZX81 which used the Z80 CPU to generate the display and so really were unable to both "think" and generate the display at the same time. On the ZX81 there were two modes, SLOW mode and FAST mode. In FAST mode the Z80 CPU prioritized computations over generating the display, so the display would go fuzzy grey while programs were runnin…

There was an adventure game that showed “The Mists of Time” for 30 seconds during initial map generation - it was a very creative way to describe the analogue tv noise caused by missing video signal.

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

#117

Post by account42 »

monkeyelite wrote: post #83
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.

4k jumped the gun. It’s just too many pixels and too many cycles. And unfortunately was introduced when pixel shaders starting doing more work. Consequently almost nothing actually renders at 4k. It’s all upscaling - or even worse your display is wired to double up on inputs. Once we can comfortably get 60 FPS, 1080p, 4x msaa, no upscaling, then let’s revisit this 4k idea.

WTF are you talking about, 60 FPS for 4K isn't even that challenging for reasonably optimized applications. Just requires something better than a bargain bin GPU. And 120+ FPS is already the new standard for displays.

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

#118

Post by account42 »

p_l wrote: post #109
hulitu wrote: post #99

Earlier quoted context omitted.

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.

DVI is just a connector - it can be either analog or digital or support both.

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

#119

Post by hollerith »

kragen wrote: post #89
hollerith wrote: post #74

Earlier quoted context omitted.

But there is less need because LCDs do not flicker (except some designed for videogames that strobe the backlight for some strange reason IIUC). I know I found the flicker of CRTs annoying even at 60 Hz.

Strobing the backlight seems like it would allow you to not illuminate the new frame of video until the liquid crystals have finished rotating, so you only have to contend with the persistence of vision on your retina instead of additionally the persistence of the liquid crystals.

My "for some strange reason" was the wrong choice of words. I don't wish to imply that I disapprove of the reason that gaming monitors do it, just that I haven't done the work to try to understand.

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

#120

Post by IAmBroom »

nradov wrote: post #79
pragma_x wrote: post #46

Earlier quoted context omitted.

It's also interesting to look at other architectures at the time to get an idea of how fiendish a problem this is. At this time, Commodore, Nintendo, and some others, had dedicated silicon for video rendering. This frees the CPU from having to generate a video signal directly, using a fraction of those cycles to talk to the video subsystem instead. The major drawback with a video chip of some kind is of course cost (…

And yet despite the lower parts count the Macintosh was more expensive than competing products from Commodore and Atari that had dedicated silicon for video rendering. I guess Apple must have had huge gross margins on hardware sales given how little was in the box.

Plus ça change...
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