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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

#31

Post by bluGill »

Suppafly wrote: post #26
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).

>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). Same, I remember installing some program that would let you quickly change the display settings on basically every computer I ever interacted with. It was especially bad if the crt was in a room with fluorescent lighting.

If your lighting and display have flicker at mathematical ratio you will notice unless the frequency is extremely high. 1:1 is most likely because it is easy to sync lights and the CRT to the AC line frequency which is 60Hz in the US (50Hz in Europe). 1:2 (used to be somewhat common) or 4:5 ratios would also cause issues.

Though now that I think of it, the CRT should be syncing with the signal and there is no reason that sync needs to be related to the AC line, but it does anyway (all the computers I know of generate their own sync from a crystal, I have no idea where TV stations get their sync but I doubt AC line frequency).

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

#32

Post by perching_aix »

bluGill wrote: post #28
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).

Have you ever seen something running at 30 Hz? Or even 15? The difference in flicker between 30 and 60 is much much larger than the difference between 60 and 120! Yeah 60 isn't flicker free, any finite number is not (there is probably quantum limits), but realistically you reach a point where you can't really tell. For most purposes 60Hz is close enough, though you can still tell.

I don't remember frankly. For what it's worth, TV sets would always be 50 Hz here (PAL) (unless they did some tomfoolery I'm not aware of and ran at 100 Hz "in secret" or something) and evidently I could watch those on end without too many holdups for years and years, so clearly it wasn't a dealbreaker. But on monitors, yeah, I just wouldn't tolerate it, whereas 85 Hz felt perfect (no discernible flicker for me that I'd recall).

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

#33

Post by sitkack »

rsynnott wrote: post #18
tom_ wrote: post #15

Earlier quoted context omitted.

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.

The 386SX was a similar story, and is normally thought of as basically 32bit. I think the perception difference may be down to timing; the 386SX came out _after_ the DX (with 32 bit data bus), so was thought of as a cheap 32bit chip, vs the 68000 which started off life with a 16bit data bus. (Fun fact: there was also the 68008, which was a 68k with an 8 bit bus!)

The 68008 saw a lot of use in embedded and could easily create a whole microcomputer on a breadboard.

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

#34

Post by JKCalhoun »

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.

Worth adding? The (almost [1]) omni-present menu bar ate 20 pixels of vertical space as well — so you could say the application had 322 of useable rows.

[1] To be sure, many games hide the menu bar.

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

#35

Post by UncleSlacky »

sitkack wrote: post #33
rsynnott wrote: post #18

Earlier quoted context omitted.

The 386SX was a similar story, and is normally thought of as basically 32bit. I think the perception difference may be down to timing; the 386SX came out _after_ the DX (with 32 bit data bus), so was thought of as a cheap 32bit chip, vs the 68000 which started off life with a 16bit data bus. (Fun fact: there was also the 68008, which was a 68k with an 8 bit bus!)

The 68008 saw a lot of use in embedded and could easily create a whole microcomputer on a breadboard.

And was also used in the Sinclair QL.

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

#36

Post by dhosek »

ChuckMcM wrote: post #11
bscphil wrote: post #8

Earlier quoted context omitted.

Looks like someone is reading Hacker News comments and editing the page - archive.org captured the page probably mid-edit, and it says "324" in one place: https://web.archive.org/web/20250527202300/https://512pixels...

Oh that's priceless. Real time HN feedback loops.

Wouldn’t be the first time.

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

#37

Post by kevin_thibedeau »

webstrand wrote: post #14
90s_dev wrote: post #13

Earlier quoted context omitted.

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

It's a great word, I use it all the time.

It usually isn't transcribed with Klingon orthography.

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

#38

Post by EndsOfnversion »

rsynnott wrote: post #18
tom_ wrote: post #15

Earlier quoted context omitted.

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.

The 386SX was a similar story, and is normally thought of as basically 32bit. I think the perception difference may be down to timing; the 386SX came out _after_ the DX (with 32 bit data bus), so was thought of as a cheap 32bit chip, vs the 68000 which started off life with a 16bit data bus. (Fun fact: there was also the 68008, which was a 68k with an 8 bit bus!)

From memory, the primary advantage of the 386SX was the ability to use a cheaper 16-bit motherboard layout and components. The lack of a 32bit bus mattered less when most software was written with 286 compatibility in mind, and the ISA bus was only 16-bits wide, which limited the utility of the 32-bit bus for fast graphics transfers.

The reduced 24-bit address bus was never a significant bottleneck during its commercial lifetime, as little consumer software at the time would require more than 4mb of RAM, and by the time it did the 486SX (32bit busses with no maths coprocessor) was the new value champion.

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

#39

Post by simne »

Impressed to see, how many people read whole article, not see just one phrase: "We don’t need a lot of the things that other personal computers have, so let’s optimize a few areas and make sure the software is designed around them".

Mac was not cheap machine and Apple that time was not rich to make unnecessary thing - they really need to make a hit this time, and they succeed.

And yes, it is true, they was limited by bandwidth, it is also true they was limited by semi-32bit CPU speed.

But Mac was real step ahead at the moment, and had significant resources to grow when new technology will arrive. That what I think lack PCs of that time.

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

#40

Post by ajross »

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…

Exactly. Like the Apple ][, the original Mac framebuffer was set up with alternating accesses, relying on the framebuffer reads to manage DRAM refresh.

It looks like DRAM was set up on a 6-CPU-cycle period, as 512 bits (32 16-bit bus accesses) x 342 lines x 60 Hz x 6 cycles x 2 gives 7.87968 MHz, which is just slightly faster than the nominal 7.83 MHz, the remaining .6% presumably being spent during vblank.

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