tl;dr: You can now embed any OS from Infinite Mac into your website, from 1984’s System 1.0 through 2005’s Mac OS X 10.4. There’s documentation for customizing and controlling embedded instances programmatically. As a demo of what’s possible, Infinite Monkey hooks up an emulated Mac 128K to OpenAI’s and Anthropic’s computer-using models, letting the technologies of 1984 and 2025 to finally meet. The instigator behind all this was Marcin Wichary, whose recent Frame of preference article is another showcase of the embedding capabilities.

A Kindred Spirit

Marcin’s articles – with their attention to detail and passion that they convey – have always struck a chord with me, whether they’re about underrated fonts or underrated movies. I’ve also appreciated that he strives for interactivity, from his Google Doodles to his Config talks. A few months ago, Marcin approached me about doing a modern take on his GUIdebook site, something with a story to tell and a way for readers to experience the material first-hand. Specifically, he wanted a way to embed emulated Mac instances in an article, ideally in as seamless of a way as possible.

Infinite Mac was already used by sites like Classic Macintosh Game Demos, DiscMaster, and Macintosh Repository to host runnable custom instances. But those were full-screen experiences and, in some cases, required a custom fork of the site. I wanted the experience to be closer to a YouTube or Google Maps embed – a snippet of HTML that’s easy to drop into any site, but still controllable via query parameters. To enable this, I added a new /embed endpoint that’s better suited to iframing. In addition to hiding the screen bezel and other chrome, it lets the embedding site control the screen resolution, get notified of the screen contents changing, and send mouse and keyboard events to the emulated Mac.

To keep embedded instances lightweight, I added an option for auto-pausing when they’re hidden. This uses both in-page (IntersectionObserver) and cross-page (visibilitychange) signals to pause and resume the emulator. Fortunately, I didn’t need to implement pausing in each emulator – instead I hooked into their input-reading loop and used Atomics.wait to cheaply suspend execution until the “paused” bit is cleared.

There were a couple of surprises along the way. First, while Chrome lets SharedArrayBuffer work in iframes (via the allow="cross-origin-isolated" attribute), this is not yet supported in Safari/WebKit-based browsers. That made my 2021-era Safari workaround newly relevant. It mostly worked, but it assumed a single global emulator instance which in Marcin’s tests had the hilarious effect of making every Mac on the page receive the same input. I added per-instance tracking so that each one gets its own event stream.

Second, Marcin noticed his custom disk images loaded much more slowly than the built-in ones. Some of that was due to them bypassing Cloudflare’s cache, but even when that was enabled, they were slower. It turned out that prefetching – added in the earliest days of the site, when all it ran was System 7 – had become even more important for more modern Mac OS versions. They read a lot more data at startup, and being blocked for 50-100ms for each chunk adds up when they need to get through a couple of hundred. Extending the prefetching to remote disks too (and caching these prefetched chunks via the service worker) shaved a lot of time off booting the Mac OS 8.5 and NeXTStep images from Marcin’s article.

I wanted to make embedding as approachable as possible (well, approachable for those interested in computing platforms from 20 to 40 years ago). There is an embed HTML builder that uses a variant of the custom instance dialog to generate the <iframe> markup for a specific instance (a construction set if you will). I also wrote documentation for the query parameters and message events to control the instance and receive state-change notifications.

Making a Demo Site

Marcin’s article is a kind of demo, and I had a crude testbed, but I wanted to more thoroughly dogfood the embedding support. It occurred to me that its capabilities (get screen content updates, send synthetic input events) made it a perfect fit for the computer use models recently launched by OpenAI and Anthropic. Their demos control a Docker container or other remote environment; having something in the browser is both satisfying (nothing to set up) and safe (the emulation sandbox already limits what the model can do).

The Mac actually has a long history of being controlled by another program, thus the Infinite Monkey site was born (as an aside, the original Monkey desk accessory is installed in the System 1.0 image if you’d like to try it out). Hooking it up was relatively straightforward, the useComputer and useChat hooks have the core glue logic. I even had Claude Code write most of the Anthropic glue code. I went with a “bring your own API key” approach – the models are somewhat expensive, and I did not want the donors to foot the bill. This does make it somewhat less accessible (the OpenAI version of the model is only available for Tier 3 accounts, and possibly not even then). The demo video should help those who don’t have access.

The actual experience of letting an LLM drive System 1.0 is a bit like a dog walking on its hind legs – impressive that it works at all, but objectively a bit underwhelming. The models are slow, it’s definitely faster to use the computer yourself (Anthropic’s own documentation calls this out). They also struggle with the UI conventions of older platforms, especially the press-and-hold mechanics of pull-down menus. OpenAI’s model can’t use them at all, since it can only request click and drag actions. Anthropic’s fares better with its separate left_mouse_down and left_mouse_up, but it often tries to click first, even when instructed otherwise.

This is just one possibility, I’m curious what other things could be built using embedded instances. And if there’s a capability that you wish they had, feel free to file an issue suggesting it.

Odds and Ends

I modernized the site’s Cloudflare setup, adopting both static assets and the official Vite plugin. Both worked as advertised: I have less code to maintain, and the local dev experience is closer to production. It was a welcome change from the usual experience on the frontend dependency treadmill.

The auto-pausing work above also suggested how I might implement a speed setting for more machine types. This fulfills a long-standing feature request to allow older software to run more accurately. It’s somewhat amusing that even in this many-layered environment (an emulator compiled to WebAssembly, which is in turn interpreted or compiled to the native platform) some things can be too fast.

Epilogue: Doctor. Manhattan has nothing on me

• It is 2006. I am working on making one website (Google Reader) embeddable in another (Gmail).
• It is 2007. I am working on making one website (Google Reader) embeddable in another (Blogger).
• It is 2008. I am working on making one website (Google Reader) embeddable in another (iGoogle).
• It is 2012. I am working on making any web app (Chrome Apps) embeddable in a host environment (Chrome).
• It is 2017. I am working on making any web app (Live Apps) embeddable in another (Quip documents).
• It is 2020. I am working on making one website (Quip chat) embeddable in another (Salesforce Lightning).
• It is 2021. I am working on making one website (Quip documents) embeddable in another (Slack).
• It is 2022. I am working on making one service (Tailscale SSH) embeddable in another (Tailscale Admin Panel).
• It is 2023. I am working on making one service (Sierra agents) embeddable in any website or iOS app.
• It is 2024. I am working on making one service (Sierra agents) embeddable in any Android app.
• It is 2025. I am working on making one website (Infinite Mac) embeddable in any other.

tl;dr: Infinite Mac can now run early Mac OS X, with 10.1 and 10.3 being the best supported versions. It’s not particularly snappy, but as someone who lived through that period, I can tell you that it wasn’t much better on real hardware. Infinite HD has also been rebuilt to have some notable indie software from that era.

Porting PearPC

I’ve been tracking DingusPPC progress since my initial port and making the occasional contribution myself, with the hope of using it to run Mac OS X in Infinite Mac. While it has continued to improve, I reached a plateau last summer; my attempts would result in either kernel panics or graphical corruption. I tried to reduce the problem a bit via a deterministic execution mode, but it wasn’t really clear where to go next. I decided to take a break from this emulator and explore alternate paths of getting Mac OS X to run.

PearPC was the obvious choice – it was created with the express purpose of emulating Mac OS X on x86 Windows and Linux machines in the early 2000s. By all accounts, it did this successfully for a few years, until interest waned after the Intel switch (sadly one of the authors passed away around then). I had earlier dismissed it as a “dead” codebase, but I decided that the satisfaction of getting something working compensated for dealing with legacy C++ (complete with its own string class, sprintf implementation, and GIF decoder). An encouraging discovery was that kanjitalk755 (the de-facto Basilisk II and SheepShaver maintainer) had somewhat recently set up an experimental branch of PearPC that built and ran on modern macOS. I was able to replicate their work without too much trouble, and with that existence proof I started on my sixth port of an emulator to WebAssembly/Emscripten and the Infinite Mac runtime.

In some ways PearPC not being actively developed made things easier – I didn’t have to worry about merging in changes from upstream, or agonize over how to structure my modifications to make them easier to contribute back. It was also helpful that PearPC was already a multi-platform codebase and thus had the right layers of abstraction to make adding another target pretty easy. As a bonus, it didn’t make pervasive use of threads or other harder-to-port concepts. Over the course of a few days, I was able to get it to build, output video, load disk images, and get mouse and keyboard input hooked up. It was pretty satisfying to have Mac OS X 10.2 running in a browser more reliably than it previously had.

Performance

While PearPC ran 10.2 more reliably, it felt slower than DingusPCC. I had spent some time last year making some optimizations to the latter, partly inspired by the TinyPPC emulator in this SheepShaver fork (aren’t all these names fun?). I ported DingusPPC’s benchmark harness and then set about replicating the performance work in PearPC (both emulators are pure interpreters driven by a lookup table, so the process was relatively straightforward). I was able to shave off about 15 seconds from the 10.2 boot time – it helps from a saving lives perspective, but is still not enough given that it takes almost 2 minutes to be fully operational. In the end, I copped out and added a UI disclaimer that Mac OS X can be slow to boot. I also got flashbacks to the “is it snappy yet?” discussions from the early days of Mac OS X – it was indeed slow, but not this slow.

Performance is still not as good as DingusPPC’s – the biggest bottleneck is the lack of any kind of caching in the MMU, so all loads and stores are expensive since they involve complex address computations. DingusPPC has a much more mature tiered cache that appears to be quite effective. More generally, while PearPC may be more stable than DingusPPC at running 10.2-10.4, it’s a much less principled codebase (I came across many mystery commits) and it “cheats” in many ways (it has a custom firmware and video driver, and only the subset of PowerPC instructions that are needed for Mac OS X are implemented). I’m still holding out hope for DingusPPC to be the fast, stable, and correct choice for the long term.

A Side Quest

I implemented the “unified decoding table” approach in PearPC’s interpreter one opcode family at a time. When I got to the floating point operations, I assumed it was going to be another mechanical change. I was instead surprised to see that behavior regressed – I got some rendering glitches in the Dock, and the Finder windows would not open at all. After some debugging, I noticed that the dispatching for opcode groups 59 and 63 didn’t just do a basic lookup on the relevant instruction bits. It first checked the FP bit of the Machine State Register (MSR), and if it was not set it would throw a “floating point unavailable” exception.

I initially thought this was the emulator being pedantic – all PowerPC chips used in Macs had an FPU, so this should never happen. However, setting a breakpoint showed that the exception was being hit pretty frequently during Mac OS X startup. The xnu kernel sources of that time period are available, and though I’m not familiar with the details, there are places where the FP bit is cleared and a handler for the resulting exception is registered. I assume this is an optimization to avoid having to save/restore FPU registers during context switches (if they’re not being used). The upshot was that once I implemented the equivalent FP check in my optimized dispatch code, the rendering problems went away.

This reminded me of the rendering glitches that I had encountered when trying to run Mac OS X under DingusPPC. Even when booting from the 10.2 install CD (which does not kernel panic) I would end up with missing text and other issues:

Checking the DingusPPC sources showed that it never checked the FP bit, and always allowed floating point instructions to go through. I did a quick hack to check it and raise an exception if needed, and the glitches went away!

The proper implementation was a bit more complicated, and I ended up revising it a bit to avoid a performance hit (and another contributor did another pass). But at the end of it all, DingusPPC became a lot more stable, which was a nice side effect. Better yet, it can run 10.1 reliably, which PearPC cannot. I ended up using a combination of both emulators to run a broader subset of early Mac OS X (unfortunately 10.0 is still unstable, and the Public Beta kernel panics immediately, but I’m holding out hope for the future).

Rebuilding Infinite HD

Part of the appeal of Infinite Mac is that the emulated machines also have an “Infinite HD” mounted with a lot of era-appropriate software to try. With Mac OS X running, it was time to build an alternate version that went beyond the 80s and 90s classic Mac apps I had collected. I had my favorites, but I also put out a call for suggestions and got plenty of ideas.

For actually building the disk image, I extended the automated approach that I first launched the site with. Disk images were even more popular in the early days of Mac OS X than they are today, so I added a way to import .dmgs as additional folders in the generated image. However, I quickly discovered that despite having the same extension, there are many variants, and the hdiutil that ships with modern macOS cannot always mount images generated more than 20 years ago. In the end I ended up with a Rube Goldberg approach that first extracts the raw partition via dmg2img and then recreates a “modern” disk image that can be mounted and copied from.

As for getting the actual software, the usual sites like Macintosh Garden do have some from that era, but it’s not a priority for them. Early to mid 2000s Mac OS X software appears to be a bit of a blind spot – it’s too new to be truly “retro”, but too old to still be available from the original vendor (though there are exceptions). I ended up using the Wayback Machine a lot. As a bonus, I also installed the companion “Developer” CDs for each Mac OS X version, so tools like Project Builder and Interface Builder are also accessible.

The only limitation that I ran into is that my disk build process is centered around HFS, but HFS+ was the default of that time period, and it introduced more advanced capabilities like longer file names containing arbitrary Unicode characters. Files from disk images that rely HFS+ features do not translate losslessly, but luckily this was not an issue for most software. To actually mount multiple drives (up to 3, between the boot disk, Infinite HD, and Saved HD), I ended up borrowing a clever solution from a DingusPPC fork: a multi-partition disk image is created on the fly from an arbitrary number of partition images that are specified at startup.

Aqua

To make the addition of Mac OS X to Infinite Mac complete, I also wanted to have an Aqua mode for the site’s controls, joining the classic, Platinum, and NeXT appearances. That prompted the question: which Aqua?

Aqua: the early years

Though the more subdued versions from 10.3 and 10.4 are my favorites, I decided to go with the 10.0/10.1 one since it has the biggest nostalgia factor. I wanted to use the exact same image assets as the OS, and since they make heavy use of semi-transparency, regular screenshots were not going to be good enough. I used resource_dasm and pxm2tga to extract the original assets from Extras.rsrc and create my own version of Aqua:

If the recent rumors of a big UI revamp do come true, it’ll be nice to have this reference point of its ancestor.

Odds and Ends

The ability to mount multiple images means that you can also have a Mac OS 9 partition and start the Classic compatibility environment (this only works under 10.1 – PearPC never supported Classic). You can thus emulate classic Mac apps inside an emulated Mac OS X inside a WebAssembly virtual machine:

There was a recent storm in a teacup about a Calculator behavior change. Using these Mac OS X images, it’s possible to verify that versions through 10.3 didn’t have the “repeatedly press equals” behavior, but 10.4 did.

Since Mac OS X boot is rather slow, I wanted to have a way to show more progress. PearPC has a built-in way to trigger verbose mode, but DingusPPC did not, so I added a way to specify Open Firmware variables at startup. This is now exposed in the custom instance dialog via the “Debug Mode” switch.

Though I’ve moved away from custom domain names, I thought macosx.app would make a nice addition to my collection. Unfortunately it’s taken, though in a rather weird way. I even contacted the YouTuber whose video it redirects to, and he said he was not the one that registered it. It expires in a couple of months, so maybe I’ll be able to grab it.

The End Of The Line?

“When Alexander saw the breadth of his domain, he wept for there were no more worlds to conquer.”
— Hans Gruber Plutarch Some Frenchman

Mac OS X support catches Infinite Mac up to the modern day, unless I happen to get access to some time travel mechanics. There are of course two more CPU transitions to go through and numerous small changes, but Tiger is fundamentally recognizable to any current-day macOS user.

Except that in the retrocomputing world, it’s always possible to go deeper or more obscure. A/UX is not something that I’m very familiar with, but it was a contemporary of classic Mac OS and would be interesting to compare to NeXTStep. Shoebill runs it, and the codebase looks approachable enough to port. Then there’s Lisa, the Pippin (DingusPPC has some nascent support), and further afield the Newton (via Einstein?). We’ll see what moves me next.

A Post-Credits Sequence

When I first began exploring ways of running Mac OS X, I mentioned that QEMU seemed too daunting to port to WebAssembly given my limited time. Furthermore, the performance of the qemu.js experiment from a few years ago made it seem like even if it did run, it would be much too slow to be usable. However, I recently became aware of qemu-wasm via this FOSDEM presentation. The performance of its Linux guest demos is encouraging: I ran an impromptu bennmark of computing an MD5 checksum of 100 MB of data and it completed it in 8 seconds (vs. 13 for DingusPPC and 18 for PearPC). There’s still a big gap between that and a graphical guest like Mac OS X, but it’s nice to have this existence proof.

Update: See also the discussion on Hacker News.

New company, new corporate blog for me to post on. Gardening Week is a post about an engineering team ritual that we've developed at Sierra. Once again you can tell that it was not ghost-written because I got to cram in a lot of links to obscure articles.

More seriously, it's been great to be at Sierra from the start and get to influence the engineering culture in such a fundamental way. I know tech company blog posts can paint overly rosy pictures, but Gardening Week is genuinely one of my favorite parts about working here.

The Macintosh Garden is a great resource in the retro Mac community. It has an archive of nearly every piece of software released in the 80s and 90s, complete with screenshots, manuals, and metadata like year of release and operating system requirements. From its debut Infinite Mac would let you use files from the Garden: download it to your computer, and then drag it in to have it appear in the “Downloads” folder.  But while doable, it’s not the same as being discoverable or pleasant to use if you wanted to do this more than a few times. 

Inspired by the CD-ROM library feature, I decided to investigate what it would take to add a “Macintosh Garden” drawer to the site. The goal was to allow any item in the Garden’s catalog to be loaded into the emulated Mac with one click (at least for the versions that support “The Outside World”, which is most from System 7 to Mac OS 9). I reached out to the Garden’s maintainer, who was on board with the project and even provided a JSON dump of the site’s catalog of 20,000 applications and games. Building the UI was a fun exercise in making the CD-ROM drawer into a reusable component - another contribution to my collection of Classic- and Platinum-themed UI controls.

In keeping with the secondary goal of Infinite Mac bringing the best of web technologies to retro-computing, I wanted the Macintosh Garden drawer to be as fast as possible. The entire catalog was 86 megabytes of JSON, which would take a while to load, even with gzip compression (27 MB). I decided to create a custom data format, with only a small index file being necessary to render the drawer list view and support search-as-you-type. It contains plain JavaScript arrays with known indices for the title, author, and other data. This approach (inspired by the JsPbLite format) minimizes redundancy while keeping decoding simple. The file is 1.5 MB, and only 439 KB when compressed with gzip, which - combined with preloading - makes the drawer pretty snappy.

A separate “details” file with descriptions, download URLs, and other information is loaded by the Cloudflare worker, which serves pieces of it on-demand. The worker also handles proxying of downloads from the Garden, both to avoid running into CORS issues and because Cloudflare’s caching should help with frequently-used items. For downloads that are large CD-ROM images, the HTTP range-based streaming approach from the CD-ROM library is also used to help with performance.

The search UI supports operators, which were implemented by a simple predicate function run as part of a linear search (the data set is small enough that fancier indexing is not required). As a small UI touch, I finally got to use scroll snap for something (the carousel view for screenshots). I also added support for triggering downloads of an item via a URL parameter, so it’s possible to share links to a favorite item.

In terms of other Infinite Mac-related work, it’s been relatively quiet. I have been tracking DingusPPC development, and it’s now possible to (sometimes, very slowly) boot Mac OS X 10.2. I also made some small quality-of-life improvements: more control over scaling, it’s harder to accidentally close the site via Command-W, and era-appropriate fonts are now used.

I was a happy user of the Dark Sky weather app for many years. Even more than the localized and timely notifications (I live in a place with predictable weather) I appreciated its Apple Watch complications. I specifically used the three-line textual summary shown in the middle of the Modular face.

My preferred Apple Watch face, circa 2022

Apple acquired Dark Sky in 2020, incorporated many of its features into the built-in Weather app (with iOS 16/watchOS 10), and shut down the original app at the end of 2022. Unfortunately the complication layout was not carried over – the only large complications are multi-hour/day graphs that have too much information and are hard to see at a glance. On my iPhone, I first switched to Weather Line (RIP) and later to Weather Strip, but neither had a watch app. I considered CARROT Weather, which has customizable complications, as a possible replacement. However, it couldn’t replicate the same layout, and paying for a separate subscription just for a watch app seemed wasteful.

On the other hand my time is free, and I figured that with WeatherKit (the one good thing to come out of the Dark Sky acquisition), I could build my own complication that showed exactly what I wanted. I procrastinated doing this for more than a year (squinting at the Weather complication every morning and thinking “I should do something about this”) but I reached a lull in Infinite Mac development and decided to once again work on an Apple platform developed in this century. It turns out that my procrastination paid off: watchOS 9 introduced WidgetKit for complications and Xcode 15 made wireless debugging (the only option for Apple Watch development) more reliable.

After fighting a bit with my old nemesis, provisioning profiles, and figuring out how to get location access in a widget (which may change in the future), I had something up and running. WeatherKit makes it particularly easy to replicate the Dark Sky complication – there’s even a property to get an SF Symbol for the current conditions and pre-computed sunrise/sunset times. 

Weather Text is the resulting app - it has a minimal watch UI to request location access and show a preview, but the main focus is the complication/widget (which also shows up in Smart Stack).

I decided not to put the app on the App Store. WeatherKit has a limited free quota, and while it was unlikely that the app would suddenly boom in popularity, I didn’t want to worry about it. I could have made the app paid up-front to deter casual installs, but my App Store account is not set up for payments, and I didn’t want to go through the hassle of that.

The app is instead available via TestFlight, which is hopefully enough of a deterrent that I’ll remain under the free limit (and builds expiring every 90 days also gives me additional control). I would have thought that only going through the lightweight TestFlight approval would exempt me from review shenanigans. However, I still had to change my original icon, despite the presence of plenty of other dark background icons, including the original Dark Sky one.

Weather Text is a home cooked meal/hammer kind of app, mostly meant for me (though I’m not the only one who misses Dark Sky’s complications). I don’t have grand ambitions for it, it’s not a forever project (modulo minimal upkeep to make sure it works with new OS releases). Though modern platforms don’t have quite as much end-user programmability as they used to (though widget.json/Widget Construction Set and Scriptable look interesting), as a middle-aged gentleman programmer it’s nice to still be able to make them fit exactly to my needs.

tl;dr: No, not Windows¹, but I’ve decided to expand Infinite Mac to the the black hardware that Mac users secretly lusted after in the 80s and 90s: NeXT.  There is now a runnable collection of all notable NeXTStep versions, going from the initial 0.8 preview in 1988 to the final OPENSTEP 4.2 release in 1997.

Porting Previous

About a year ago I came across the Previous emulator – it appeared to be a faithful simulation of the NeXT hardware and thus capable of running NeXTStep. While including it in Infinite Mac would be scope-creep, NeXT’s legacy is in many ways more relevant to today’s macOS than classic Mac OS. It also helped that it’s under active development by its original creator (see the epic thread in the NeXT Computers forums), and thus a modern, living codebase².

Previous is the fifth emulator that I’ve ported to WebAssembly/Emscripten and the Infinite Mac runtime, and it’s gotten easier. As I'm doing this work, I’m developing more and more empathy for those doing Mac game ports – some things are really easy and others become yak shaves due to the unintended consequences of choices made by the original developers. Previous is available on multiple platforms and has good abstractions, so overall it was a pretty pleasant experience.

The main challenge was the pervasive use of the SDL library – I don’t want any of it as a platform abstraction, since I have my own. I chose to replace the entry-point and several subsystems to avoid bringing in too much SDL code. Even with that, I still needed to have some stub files for dependencies that I couldn’t omit altogether. On the other hand, it was a pleasant surprise that adding sound support was trivial — the APIs that it needed mapped 1:1 with the ones I’d already exposed from the Infinite Mac runtime.

With the initial emulator being brought up, there were some more fun tasks, like adding a NeXT-style monitor frame and a NeXT appearance to the Infinite Mac controls (working on them is giving me Kaleidoscope scheme flashbacks).

Once I had Previous running I did some profiling and was discovered the same excessive wasm-to-js/js-to-wasm ping-ponging that I noticed in DingusPPC – it also uses setjmp/longjmp to implement an exception handling mechanism for the MMU. The fix was also very similar: intentionally add an extra wrapping function that contains the CPU emulation loop.

The performance impact of the fix was not as noticeable because Previous tries to accurately simulate the performance characteristics of the original hardware (this is also why boot times are much longer). In fact, I had originally missed the speed checking that the native main loop does, and the emulator was running too fast, leading to timing-dependent things like double-clicking not working.

Speaking of mouse input, Previous uses relative mouse input — it accurately simulates real hardware so all it can do is behave as though a physical mouse is moving and generating updates. This was the case with DingusPPC too, and while the Pointer Lock API makes this work reasonably well on desktop browsers, it’s not a good fit for the mobile web. To make input more accessible on touch-enabled devices, I added a virtual trackpad mode that turns swipes and taps on the screen into mouse movements and clicks. This also helps with double-clicking and making pre-Mac OS 8.0 pull-down menus more usable, though it is somewhat finicky to trigger the drag-lock gesture (I now see why it’s so hard for other touchpad vendors to replicate all of Apple’s gestures).

As part of doing some of the integration work I became aware of just how much of a minority player NeXT was in the 80s and 90s computing world (even more so than Macs). For example, they had their text encoding/character set, and while Python (and other systems) have native support for the contemporary MacRoman encoding, I had to add my own to handle NeXT’s. Similarly, there is a convenient Python library for dealing with HFS disk images, but I could not find any for the UFS variant that NeXT used³.

The disk images with NeXTStep installs are quite large (hundreds of megabytes per version), and the Workers KV-based storage that I had been using was becoming increasingly ill-suited for them (and expensive). As part of this project I also switched to Cloudflare R2 (their S3-like object storage system). On one hand I’m not thrilled with the site becoming dependent on additional services, but on the other I do want to keep costs down. Luckily the dependency is not invasive — it would be trivial to store the disk chunks anywhere else (or to keep storing them as static files, the way I do in the local dev server).

Exploring NeXTStep

Although I was familiar with NeXTStep at a theoretical level and had spent a few hours using a slab in the mid 1990s, this was my first time using it in-depth. My first observation was that having it side-by-side with the contemporary Mac system software makes it even more apparent how much of an advance it was.

System 6.0 and NeXTStep 0.8: two very different releases from 1988

Strategy du jour: productivity (NeXTStep 2.0), multimedia and internationalization (NeXTStep 3.0), object-oriented development (NeXTSTEP 3.3)

I was also amused to notice a parallel with the early Mac system releases: the initial release is hard to find in pristine form (a copy of System 0.97 was only tracked down late last year). In both cases it’s it because of the very small number of copies produced, and because they shipped on read/write media (floppy disks for the Mac, magneto-optical disks in NeXT’s case), and thus ended up being used for personal storage too. For NeXTStep 0.8 the archive of images that forum member mikeboss created was the best source that I could find, though I’m happy to switch things over if a better one turns up.

As part of installing all of the OS versions I discovered that starting with NeXTStep 3.0 there is support for the HFS file system used by contemporary Macs. This means the Saved HD drive that has persistent storage also ends up working here. It can even be used as a virtual sneakernet to move data between NeXT and Mac installations on Infinite Mac (which means that it’s possible to get data in and out of the machines via Macs which have “The Outside World“ drive).

To make the systems more than a quick curiosity, I also created a NeXT version of the “Infinite HD” drive with pre-installed software. I had read stories about Doom and WorldWideWeb being developed on NeXTStep, and it was nice to make them accessible. I also added a NeXT version of the CD-ROM library feature, with one-click access to disks that have been preserved at the Internet Archive.

As part of finding more NeXT software to try out, I came across Daydream, which allows Mac software to run on black hardware. It’s technically not an emulator, instead it takes advantage of the fact that NeXT and Macs both used the Motorola 68K CPUs. It effectively turns your NeXT machine into a Mac that you dual-boot via the help of an adapter kernel. The original version needed a hardware dongle with genuine Mac ROMs, but a few years ago the NeXT Computers forum resurrected it such that it can run entirely via software. It’s this variant (known as Darkmatter) that is included on Infinite HD. In some ways this justifies the whole Previous side-quest — it’s just a more convoluted way to run the same classic Mac software as the rest of the Infinite Mac emulators.

Things happen

Christopher Nolan (sort of) knows about Infinite Mac. I did a minor site redesign. After recalling the KanjiTalk New Year’s Day easter egg, I added custom date/time support so can you see it anytime you want. Infinite Mac is being used as a tool to make Playdate game art and other toys. You can now load files with resource forks straight from the macOS Finder. Apeiron now works. And most excitingly, DingusPPC has progressed to point where the Mac OS X 10.2 installer starts up.

Update: See also the discussion on Hacker News.

1. Also, PCjs already has the Windows niche well-covered
2. andreas_g is the Previous author, and he was very helpful in the thread I started about my porting work
3. I did take a stab at writing a HexFiend template for UFS/NeXT partition maps
4. See these pages for details on the capitalization rules.

I had previously mentioned that I ended up fixing some DingusPPC CPU emulation bugs. This was my first time working at this (lower) level of the Infinite Mac emulators, and I thought it would be interesting to write up such an investigation.

There was an issue that was immediately apparent when I first got DingusPPC building: while starting up from the 7.1.2 Disk Tools floppy would result in a functional-looking Finder, doing the same from the 7.1.2 install CD would end up with many rendering glitches — notably no text, but also missing icons.

7.1.2 Disk Tools Finder

7.1.2 Install CD Finder

Classic System Software is mostly a closed-source black box (outside of leaks), and while DingusPPC is open source, it’s a codebase that is still pretty foreign to me. In the absence of other ideas, I figured that creating a more reduced test case would be a good use of time. This reminded me of my investigations into Chromium/WebKit rendering bugs, where half the battle was reducing a complex web page down to a minimal test case.

I examined the two system folders and observed that the CD-ROM one was quite a bit larger, with additional extensions, a different enabler¹, and a bigger System suitcase.

I created a read-write copy of the CD-ROM system folder and used a native build of Basilisk II to operate on it, removing or switching out files one a time to morph it into the floppy version, and looking for any differences when booting it in DingusPPC. It turned out that switching out the “Minimal PowerPC Enabler” on the floppy with the full “PowerPC Enabler” one from the CD-ROM was the key difference — with the full enabler text would not render.

I then opened the two enablers in ResEdit and compared them — the full one had a bunch more resources. I thus repeated the process, deleting extra resources one at a time to morph the full enabler into the minimal one.

It turned out that the culprit was the ntrb resources, specifically removing ID 16 (StdTextTraps) and 18 (QuickDrawTextTraps) would restore text rendering. They contain PowerPC executable code — the giveaway is the Joy!peff prefix that is the header of the Preferred Executable Format. “Traps” refers to the system/Toolbox calls. My assumption is that the ROM of the first generation of Power Macintoshes was finalized relatively early, and contained mostly 68K code that would need to be emulated². The PowerPC enabler contained native implementations of more of the Toolbox, which were loaded in via these ntrb resources. These particular resources had native implementations of the text subsystem, which was very much in line with where the buggy behavior was.

Between resource_dasm and some help from DingusPPC Discord member joevt I was able to get a list of the 14 Toolbox traps that were being reimplemented as native PowerPC versions. The one that immediately stood out was StdTxMeas – here’s a description of it from Inside Macintosh: Text:

The QuickDraw text routines use two of the bottleneck routines extensively—one to measure text (StdTxMeas) and one to draw it (StdText). Most of the high-level QuickDraw text routines call the low-level routines. The use of bottleneck routines provides flexibility to QuickDraw and applications that need to alter or augment the basic behavior of QuickDraw.

While I had significantly narrowed where things were going wrong, I was reaching the limits of what I could via basic file system and ResEdit hacking. Ideally I would have a simple test program that just called StdTxMeas, so that I could examine its behavior in isolation.

It was thus time to crack open CodeWarrior and write a simple test program. I used the SillyBalls sample code as a starting point — there certainly used to be a lot of boilerplate in getting a basic window up on the screen. I created a simple test function that draws a string and then its bounding box as determined by StdTxMeas. Lacking the ability to render debugging text, I used FrameRect as the output mechanism.

void TestStdTxMeas(WindowPtr mainWindowPtr) {
    Rect measureRect;
    Str255 testString = "\pHello World";
    Point number = {1, 1};
    Point denom = {1, 1};
    FontInfo fontInfo;
    int width;
    
    SetPort(mainWindowPtr);
    MoveTo(20, 20);
    TextSize(12);
    
    DrawString(testString);
    
    width = StdTxMeas(testString[0], testString + 1, &number, &denom, &fontInfo);
    
    // +1 for the width so that if we get a zero we can still see the rect.
    SetRect(&measureRect, 20, 8, 20 + width + 1, 24);
    FrameRect(&measureRect);
}

I set the program as the startup item (so that I wouldn’t have to navigate blindly in a half-drawn Finder window) and observed its behavior under both emulated and native implementation of the text traps.

Sure enough, it looked like when using native PowerPC code, StdTxMeas would end up returning 0 instead of the expected value. I suspected a bug in DingusPPC’s PowerPC CPU emulation, but it was unclear where. I had some false starts:

1. I tried to disassemble the StdTxMeas implementation – I got lost when going through too many layers of indirection due to the calling convention.
2. I looked at its 68K implementation and checked some of the intermediate building blocks – the width table looked correct.
3. I tried to get MacsBug running so that I could single-step through it – I was not able to get it to succesfully suspend execution under DingusPPC.

As a variant of attempt 3, I decided to make DingusPPC output the instruction stream that it was executing, hopefully there would be a clue where the problem was. To signpost the instructions that represented the implementation of StdTxMeas, I did two otherwise no-op divisions by specific literals (the MoveTo call is to ensure that the compiler didn’t decide to optimize them out).

GetPen(&pen);
pen.h = pen.h / 32749;

width = StdTxMeas(testString[0], testString + 1, &number, &denom, &fontInfo);

pen.v = pen.v / 32719;
MoveTo(pen.h, pen.v);

Checking the CodeWarrior dissembly I could see the expected li (load immediate) and divw (divide word) op codes:

// pen.h = pen.h / 32749;
    
000000A0: A861003A  lha      r3,58(SP)
000000A4: 38807FED  li       r4,32749
000000A8: 7C6323D6  divw     r3,r3,r4
000000AC: B061003A  sth      r3,58(SP)

I could thus look for the 32,749 divisor in DingusPPC’s divw implementation and then set a flag to trigger its built-in disassembler (and turn it off when the divison by 32,719 occurred). 

Out of this I had a list of 635 instructions that were executed, which was a lot, but still made for a starting point. Looking at counts of the types of instructions, there were 59 unique ones, with loads and stores being the most common. I figured that the most popular instructions were least likely to be buggy, otherwise more things would have been broken. Looking at the bottom of list, two stood out: nabs (negative absolute) and doz  (difference or zero). They both had no coverage in DingusPPC’s test suite³ and were obscure — they are actually part of the POWER instruction set that was the predecesor of PowerPC, and were only included in the PowerPC 601 chip to help with IBM’s migration to it.

Looking at the implementation of nabs, it seemed relatively straightforward — it would always set the sign bit to to 1, thus making the number always negative:

ppc_result_d = (0x80000000 | ppc_result_a);

However, negative numbers are not actually represented as positive numbers with the sign bit set, they use two’s complement. Using Julia Evans’s handy integer.exposed we can see the representation of 123, -123 and 123 with its sign bit flipped, and thus why this implementation is not right.

I switched it out to the more readable explicit sign test and negation:

ppc_result_d = ppc_result_a & 0x80000000 ? ppc_result_a : -ppc_result_a;

Things still weren’t working, but as I had previously mentioned, doz was also suspicious (and it was the instruction that was executed right before nabs). I noticed a copy/paste error in which register the result was being stored in, and once I fixed that, everything began to work!

This whole investigation took about a week’s worth of evening hacking time, and there was a bit of luck involved in the end. I very easily could have ended up on a wild goose chase looking at some of the other infrequent instructions, and given up before I got to nabs and doz. Or the implementation bugs could have been much more subtle. However, it worked out, and it was really satisfying to be able to contribute to the DingusPPC core.

1. System enablers were used to patch in support for Macintosh models released after a base version of the OS shipped.
2. Much of the Toolbox code was written in 68K assembly and so could not be easily ported when Apple made the 68K-to-PowerPC transition in 1994. Emulation was thus the solution not just for older software, but also for large parts of the OS too. It was not until the transition to Mac OS X in 2001 that the need for 68K emulation went away.
3. The DingusPPC test suite is partially based on the one for the Dolphin emulator. Since that emulates a G3-class CPU, it does not need to worry about the quirks of first-generation PowerPC CPUs.