[HN Gopher] The Apple IIGS Megahertz Myth
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The Apple IIGS Megahertz Myth
Author : rbanffy
Score : 99 points
Date : 2024-08-16 17:08 UTC (5 hours ago)
(HTM) web link (www.userlandia.com)
(TXT) w3m dump (www.userlandia.com)
| cainxinth wrote:
| I still have my childhood IIGS. It sat in my folks' poorly
| insulated attic for two decades before I rescued it, and it
| booted up on the first try! They don't make 'em like they used
| to.
| rbanffy wrote:
| Apple II's were designed for the most computer-hostile
| environments in existence: primary schools.
| buildsjets wrote:
| Replace the 3.7v lithium backup battery for the RTC before it
| blows up and spews acid all over your board! ROM01 versions
| have it soldered in, ROM03 is in a battery holder. Replacements
| for both are readily available.
| cainxinth wrote:
| I did not know that and will investigate. Thanks!
| kevin_thibedeau wrote:
| Their power supplies have RIFA brand capacitors in the power
| supply. Their cases are 100% guaranteed to be cracked from
| moisture ingress at this age. They _will_ fail catastrophically
| when you plug it in at some point. If you want to keep it
| running, you need to replace the supply or recap it (Just the X
| & Y RIFAs).
| jmbwell wrote:
| This was a fascinating and ... detailed ... story. I appreciate
| that it went a little further into the history of Apple's
| involvement ARM than the recent spate of blog posts that didn't
| go back past Newton.
| rbanffy wrote:
| I too was surprised at how detailed it was. Learned a lot in
| those 50 minutes or so.
|
| Plus, the Apple Iix mock-up is a beauty. I'll need to order a
| 50cm x 50cm 3D printer and find the right filament color for
| the Snow White look.
| nazgulsenpai wrote:
| I watched his YouTube video on this a few days ago. It goes
| WAAAAAY more in-depth than you'd expect and is a great hour of
| second-monitor viewing.
| nsxwolf wrote:
| I can't listen to that much alliteration. I had to stop pretty
| early on.
| rishabhd wrote:
| Love the story and MGS2 reference.
| kefkafloyd wrote:
| Thank you for catching the reference. And for enjoying the
| story.
| fortran77 wrote:
| I'll never forgive Apple for breaking their promise of "Apple ][
| Forever." (https://www.youtube.com/watch?v=RHCp0nuA4xA)
| taylodl wrote:
| They got a good run out of that platform, longer than most. But
| the NeXT platform has gotten a longer run...
| rbanffy wrote:
| It's one of the best cases of "reverse acquisition". It's
| like NeXT acquired Apple for one Steve Jobs (and an OS) and
| got $400 million as change.
| fzzzy wrote:
| I always say NeXT aquired Apple for -400 million.
| rbanffy wrote:
| I still say they should release a beige Apple IV as an apology
| for the Apple ///.
| jdswain wrote:
| I think the built-in keyboard idea had run its course, so any
| possible Apple IV would probably end up looking a lot like an
| Apple IIgs. The little keyboard extension on the IIgs case is
| kind of reminiscent of the Apple ///.
|
| It would have been good to end the line with what was planned
| for the Mark Twain, internal floppy and hard disks would have
| made the whole system a lot better. And of course if we could
| have got a 14 MHz 65C816 as well then it would have been a
| really interesting system.
| rbanffy wrote:
| It can still look like a /// with a detached keyboard
| that's a continuation of the main case. Commodore did that
| with their office machines (the rounded ones).
|
| I think the beige is important as part of the apology ;-)
|
| Frankly, I'd accept a beige Mac Mini with a rainbow Apple
| logo on top and call it a day.
|
| I'm sure Tim Cool lurks around these pages.
| dhosek wrote:
| I remember being surprised to see someone with an Apple IIgs
| when I was in undergrad (late 80s) and discovering the platform
| still lived. The fact that they were still selling the Apple II
| line in 1993 (1995 if you count the Mac add-in card) seems
| pretty damn miraculous to me.
| zerocrates wrote:
| K-12 schools are obviously their own whole situation, but in
| a well-funded, well-regarded public school system we were
| using Apple IIs in the mid-90s. Of course this was elementary
| school and not a college.
|
| By middle school it was PowerMacs and by high school it was
| Windows 2000.
| justanother wrote:
| That rabbit hole goes pretty deep.
|
| In the early 1990s, the IIgs community went through this sort
| of "faux workstation" phase where we had 16MHz hotrodded
| accelerator cards, high(er) resolution graphics cards like
| SecondSight, and a pre-emptive multitasking operating system
| (GNO/ME) along with the beginnings of TCP/IP support (gstcp).
| If you squinted one eye, we could almost hold our own against
| something like SPARCStation 1 as long as you didn't want to
| run Mosaic. You could fire up a desktop with a few shell
| windows and compile C programs and telnet out while playing
| SoundSmith (not-quite-.MOD) songs. That is to say, we were
| pushing the whole mess beyond anything a sane person would
| even fever-dream of attempting.
|
| The community today is putting out more releases more
| steadily than any other era I can recall since then, but we
| seem to have mostly backed off of the whole "workstation"
| application that was in a few dorm rooms at the time.
|
| Edit: FWIW I just noticed the date today. Happy 8/16!
| rbanffy wrote:
| I remember how a 1MHz 6502 easily smoked a 4MHz Z-80 back in the
| day. Apple _could_ have followed on the II with at least a 2 MHz
| model.
|
| I wonder at what other clocks did the WDC 65C02 support?
| dhosek wrote:
| But so much of the Apple II design was focused around
| minimizing chip usage and counted on exact timings that I don't
| know that it would have been possible to change the clock
| speed. Add in the fact that there was no access to a real time
| clock so things like timing delays counted on things like run
| this empty loop 100 times, or the fact that the graphics memory
| layout was tied to how the electron beam on the monitor
| refreshed pixels or the reliance on a quirk of timing of the
| 6502 processor in the disk II controller hardware and I don't
| know that a 6502 at a different speed could possibly work.
| icedchai wrote:
| There were Apple II accelerators, like the Zip chip. Some
| clones, like the Laser 128/EX, also ran at higher speeds.
| Findecanor wrote:
| There was a 4 MHz 65C02 model .. but not until 1988: The
| Apple IIc+.
|
| You could lower the clock speed to 1 MHz for programs that
| relied on it, but the 65C02 did not support the
| unofficial/undocumented instructions of the original 6502 so
| there were still some programs that did not work.
| TMWNN wrote:
| >But so much of the Apple II design was focused around
| minimizing chip usage and counted on exact timings that I
| don't know that it would have been possible to change the
| clock speed.
|
| A recent Adrian's Digital Basement video
| <https://www.youtube.com/watch?v=dt1eSXpo1SA> discusses this
| topic. While showing how a 80286 system runs at 1MHz, he
| discusses how the PC architecture allows (most) software to
| run at that clock speed while the Apple II architecture and
| software are inherently tied into the 1MHz clock speed.
|
| In retrospect it seems so sensible to have the IIe and IIc in
| 1983 and 1984 move to, say, 2MHz, that I'm sure that fears of
| breaking software compatibility contributed to that from
| happening. (That almost certainly would have been a short-
| term problem. Given how quickly the Apple II software moved
| en masse to 128K/80 columns by the mid-1980s, developers
| would have accounted for a faster clock speed too.)
| rbanffy wrote:
| The Apple /// ran at 2MHz but would slow down to 1 for
| expansion bus IO and Apple ][+ emulation.
| TMWNN wrote:
| The III's II compatibility mode ramps that down to 1MHz,
| and has other restrictions to make sure that II software
| cannot use any III-only features.
|
| Without III sucking up all of Apple's R&D budget and
| attention c. 1979-1980, the Apple II would surely have
| seen earlier enhancements. The II+ (1979) would likely
| have had lowercase and better keyboard (which did not
| occur until IIe in 1983), and a new model in, say, 1981
| might have shipped with an optional Apple 80-column card
| (again, with the IIe in actuality). Built-in 128K RAM
| probably would not have occurred until 1984, akin to the
| IIc's introduction, but earlier support for RAM expansion
| alongside 80 columns is possible. One of these models
| would likely have had the 2MHz clock, too, while no II in
| actuality shipped with a faster clock until IIgs in 1986.
| rbanffy wrote:
| The big deal is video and RAM timing. If the memory is twice
| as fast, you'll still be able to read from it for the video
| refresh at times the CPU won't be able to. Also, I think DRAM
| refresh was done on the video timing. You'd need to rework
| all the logic on the board, but that was doable when they
| built the Mega 2 chip (and done in the IIgs FIP). The
| trickiest part would be the Disk ][ interface, and disk I/O
| done on it, as everything was timing-critical. A different
| disk controller that doesn't rely on timings would be able to
| function.
|
| As for program timings, you don't need an RTC. You want
| timers and interrupt generators. I believe the //e and the
| //c could generate interrupts on vertical blanking. For a
| game you could run all logic and drawing and set up the
| interrupt vector so that the next interrupt starts the next
| game cycle. To count time, a cycling timer that increments on
| vblank would be quite enough. IIRC, MSX had one of those.
| gallier2 wrote:
| Apple /// was 2MHz and it was a disaster.
| jdswain wrote:
| It slowed down to 1 MHz for I/O and Apple ][ compatibility.
|
| I wouldn't call it a disaster, sales and marketing wise
| mainly, but that also had a lot to do with the IBM PC coming
| out around the same time.
|
| It was probably the most complex 6502 design, and mainly
| consisted of discrete logic chips rather than custom chips
| that other manufactures were starting to use. It had advanced
| features like an additional addressing mode to access up to
| 512k RAM without bank switching. (Plus two speed arrow keys)
| muziq wrote:
| I don't know how you remember that considering it doesn't.. I'm
| as rabid a 6502 fanboy as you might meet (and have been
| programming them for some 40 years or so), but that's not a
| competition it wins, all 6502 coders know that ;) We think it
| does because usually the 6502 machines have oodles of
| (ab)useable hardware ;)
| jdswain wrote:
| Rockwell and WDC had 65C02's up to 4 MHz relatively early on,
| but the 4 MHz versions seemed to be quite rare. WDC now has
| 65C02's rated at 14 MHz, but they go quite a bit higher than
| that if you've got fast enough RAM.
|
| There are some technical details on why a 4MHz Z80 is roughly
| equivalent to a 1MHz 6502. As always with processor design
| there are tradeoffs in every decision. The Z80 had a 4-bit ALU,
| but I'm not sure if that slows it down.
|
| The Z80 has a more complex architecture than the 6502. A 6502
| clock cycle is one bus cycle and simple instructions can
| execute in one clock cycle. For the Z80 a clock cycle is called
| a T-state, and one machine cycle consists of multiple T-states.
| A simple instruction like INI takes 4 T-states.
| classichasclass wrote:
| Not quite: the design is such that even the fastest 6502
| instructions are two cycles. Still, generally quicker clock-
| for-clock than a Z80.
| twoodfin wrote:
| To me the most fascinating nugget of history was how close a
| young Tony Fadell (later General Magic, iPod, Nest) came to
| supplying high-speed 65816 chips!
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(page generated 2024-08-16 23:00 UTC)