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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

#61

Post by wmf »

danudey wrote: post #52
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.

I have a 4k 60Hz monitor connected to my laptop over one USB-C cable for data and power, but because of bandwidth limitations my options are 4k30 and USB 3.x support or 4k60 and USB 2.0. I love the monitor, it's sharp and clear and almost kind of HDR a lot of the time, but the fact that it has a bunch of USB 3.0 ports that only get USB 2.0 speeds because I don't want choppy 30Hz gaming is just... weird.

Everything is amazing and nobody's happy.

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

#62

Post by monocasa »

tom_ wrote: post #55
silvestrov wrote: post #21

Earlier quoted context omitted.

No, this is very wrong. The 68000 is 32 bit internally and it has 32 bit registers: https://en.wikipedia.org/wiki/Motorola_68000 Externally it had 16 bits for databus and 24 bits for addresses. That is why we later got the 32 bit clean ROMs as Apple used the upper unused 8 address bits for flags.

The cycle counts really don't back this theory up. And indeed, from that link: > Internally, it uses a 16-bit data arithmetic logic unit (ALU) and two more 16-bit ALUs used mostly for addresses,[4] and has a 16-bit external data bus.

Like a lot of things, the taxonomy kind of breaks down at the edges and arguments can be made either way.

I will throw out there though that ALU width and buses are generally seen as orthogonal to 'bitness' of a processor, and more an implementation detail. The Z80 had a 4bit ALU, but is considered an 8bit CPU. The PDP-8/s and SERV have single bit ALUs, but are considered 12 and 32 bits respectively. The 8088 is considered a 16bit CPU despite having both an 8bit ALU and bus.

'Bitness' is generally defined more as 'what is the width of whatever is the closest thing to a GPR'.

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

#63

Post by nothercastle »

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…

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?

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

#64

Post by MBCook »

nothercastle wrote: post #63
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…

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?

If you’re used to seeing 60Hz everywhere like Americans are 50Hz stands out like a sore thumb.

But mostly I suspect it’s just far easier.

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

#65

Post by Jaygles »

wmf wrote: post #61
danudey wrote: post #52

Earlier quoted context omitted.

I have a 4k 60Hz monitor connected to my laptop over one USB-C cable for data and power, but because of bandwidth limitations my options are 4k30 and USB 3.x support or 4k60 and USB 2.0. I love the monitor, it's sharp and clear and almost kind of HDR a lot of the time, but the fact that it has a bunch of USB 3.0 ports that only get USB 2.0 speeds because I don't want choppy 30Hz gaming is just... weird.

Everything is amazing and nobody's happy.

Identifying areas to improve is how we make progress

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

#66

Post by MBCook »

pragma_x wrote: post #46
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…

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 (…

Plus those weren’t raw bitmaps but tile based to help keep memory and bandwidth costs down.

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

#67

Post by kstrauser »

90s_dev wrote: post #13
johnklos wrote: post #2

The title is incorrect, because b&w Macs have 512×342 resolution, not 512x324. It wouldn't've been too crazy had Apple went with 64K x 4 chips, so they'd've just needed four of them to get 128 KB at a full 16 bits wide. 512x342 was 16.7% of 128 KB of memory, as opposed to 18.75% with 512x384. Not much of a difference. But having square pixels is nice.

> wouldn't've Really, John? You really had to make me parse that word?

Who’d’ve thought?

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

#68

Post by kstrauser »

monocasa wrote: post #62
tom_ wrote: post #55

Earlier quoted context omitted.

The cycle counts really don't back this theory up. And indeed, from that link: > Internally, it uses a 16-bit data arithmetic logic unit (ALU) and two more 16-bit ALUs used mostly for addresses,[4] and has a 16-bit external data bus.

Like a lot of things, the taxonomy kind of breaks down at the edges and arguments can be made either way. I will throw out there though that ALU width and buses are generally seen as orthogonal to 'bitness' of a processor, and more an implementation detail. The Z80 had a 4bit ALU, but is considered an 8bit CPU. The PDP-8/s and SERV have single bit ALUs, but are considered 12 and 32 bits respectively. The 8088 is cons…

Seconded. If you were an ASM programmer, you’d have no idea it had a 16 bit ALU. All the ops were 32 bit, regardless of what the underlying silicon looked like.

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

#69

Post by brookst »

90s_dev wrote: post #13
johnklos wrote: post #2

The title is incorrect, because b&w Macs have 512×342 resolution, not 512x324. It wouldn't've been too crazy had Apple went with 64K x 4 chips, so they'd've just needed four of them to get 128 KB at a full 16 bits wide. 512x342 was 16.7% of 128 KB of memory, as opposed to 18.75% with 512x384. Not much of a difference. But having square pixels is nice.

> wouldn't've Really, John? You really had to make me parse that word?

You version of shouldn’t’ve’s punctuation isn’t like that?

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

#70

Post by sgerenser »

phendrenad2 wrote: post #56

I always assumed it was a compromise between memory usage, refresh speed, and the GUI that they wanted. Don't forget that the Macintosh was preceded by the Lisa (800x364) and the IIGS (640x200), so they probably had a good sense for what was comfortable given a certain resolution.

The IIGS came out well after the original Macintosh: https://en.wikipedia.org/wiki/Apple_IIGS
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