Apple releases firmware fix for heat-related throttling issue with newest MacBook Pros

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I’m not going to say it is impossible, but a software fix for a thermodynamic problem seems rather unlikely.

At least in terms of being able to run the processor at its maximum capabilities 24/7.


I’ll assume you implied a “and keep the same performance spec” (eta, or you could add that while I was typing)

software can limit the power consumption and therefore heat generation, at the expense of performance.

Correct, I was editing to add that in when you replied.

I mean, it’s not like a good multithread benchmark wouldn’t show the performance to be degraded compared to an i9 that isn’t thermally or software limited.


Maybe it’s like the VW software fix.


If it shifts the screen to bluer colors, orders cold drinks for the user, invites others over and/or initiates calls with interesting people to distract the user from the computer and reduce usage, plus uses IoT to reduce room temperature by controlling the thermostat, I could see it plausibly fixing some onboard thermodynamic problems. Even just sending snaps a stream from the built-in-camera to the user’s boss/clients could easily lead to firing and a dramatic reduction in the workload and therefore thermal load to manage.


Anyone have an idea of what they mean by this? It sounds most like someone saying that there was an issue with an ACPI thermal zone’s definitions(I’m assuming ‘key’ as in ‘key/value’) that caused less elegant than desired state transitions; but that’s basically pure speculation.

(edit: an intriguing theory has surfaced to the effect that the problem is actually related to the CPU being set to try to draw substantially more power than the VRM can handle more than momentarily; then getting throttled down hard when the VRM overheats and tries to save itself. Allegedly these…optimistic…VRM draw values aren’t new; but a CPU that says “125 watts? Challenge Accepted.” has brought a formerly obscure setting to light.

If true this would be a bit of a downer. The VRM is too unassuming to get much attention; but unless you think that +12v is a totally OK Vcore for contemporary CPUs it’s a component you want to keep happy.)

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It’s actually been happening quite a bit lately.

Cooling and fan speeds are controlled by software. Often bios or things like chipset or gpu firmware. Basically there are predefined curves for fan speed vs component temperature. This temp fans off/low, this temp fans medium, this temp fans high. Hotter the component gets higher the fan goes, usually in preset steps. If those aren’t set right the fans won’t ramp up as heat goes up. Or won’t blow the appropriate amount of air given the heat generated. And you end up overheated or throttled when you shouldn’t be. The cooling can handle the heat. The cooling just doesn’t kick in.

Update that bit of software and things can be fine.

There’s been a couple of GPUs out in the last 2 years where the default fan curve was set badly. Some early amd/ryzen motherboard’s shipped with bios that had bad default fan curves. There’s been some issues with windows over riding or interfering with fan speeds set with certain parts. And driver bugs where manually setting fans would basically force a broken fan curve.

All pretty easily fixed with software updates.

It’s usually pretty easily identifiable though. There are simple ways of checking fan speed and you can see it’s not speeding up when it should. Even without that you can hear it. So this may be less of a bug than “we set the fan curve too conservatively because we wanted low noise”. Which also happens.


See above. Near as I can tell they’ve just tweaked when the fan starts going, And how fast it goes. The “missing digital key” would appear to refer to a step in the fan curve. Probably missing whatever tells the fans to go to Max when it crosses a certain temperature. Or they added a higher speed to the top of the curve to compensate for heat they didn’t expect.


Let me just say as a Volkswagen Diesel owner:

You are correct, sir!


Computers have fans. Fans cool down the hardware. Macs have fan management firmware. An error in the firmware caused the fans to not ramp up as they are supposed to when things get too hot. This caused the CPU to throttle under load.

Keep in mind that the default setting for nearly all macs is to not ramp up the fan until the CPU is redlining. For example, by default my 2009 Mac Mini does not speed up its fan until the CPU gets over 85° or so. At which point it turns the fan up all the way so it sounds like an angry jet engine. All I have to do is manually adjust the lowest fan speed from “completely inaudible” to “low murmur that can be heard in a quiet room” and the idle temperature falls from 50° to 35°, with the load temperature never exceeding 60° instead of getting up into 80-90° territory (ambient room temperature kept at 25 or 26, and yes we use centigrade here in Canada, deal).

Someone’s cat walked across the keyboard and entered incorrect values into the table of default speeds for a given temperature in the fan control firmware.


Likely a simplified view, actually. All sorts of hardware tuning parameters are exposed to software, including numerous settings around things like memory timings and maximum CPU wattage. The hardware uses this for automatic control independent of the OS (you don’t want an out of control system using 100% of the CPU to also not be telling the fans to spin up).

The delta between minimum and maximum power consumption has gone up considerably over the last ten years, as more and more focus has been put on mobile devices and computing. Likewise, the complexity of these controls has increased. Nowadays, the CPU is tuned for the computer it is put in (including, across ultrabook models, having the same processor run at different base clocks depending on the cooling/power capabilities of the system)

Intel chips can run very fast if not for those excess power and excess heat problems - they have surpassed the heat density of a fission reactor at max usage. So they now have a numerous dynamic adjustments, such as a base clock and ‘turbo’ max frequency. - the system can draw more power and run faster to finish tasks faster. But this generates heat, and can only be used short-term.

I expect Apple’s firmwares were for whatever reason (oversight on the release process?) were not limiting the power draw properly, causing systems to critically overheat. Then, the hardware throttles them down in an emergency mode until the heat dissipates - then more than likely, max draw again for a short period of time until the next overheat cycle.

Its not just the fans, because the system components (including the CPU itself) just aren’t designed to permanently operate at turbo speed.

Simplistic analogy time - it’s like the old NES game Excite Bike - if you just hold on the accelerator, your bike will overheat and you will just sit on the side of the track for a while. The new firmware tells the laptop to take its foot off the accelerator before that happens.


“Looks like the usual adage of “Get your Mac laptop with the best ram/processor/storage you can afford” is once again viable advice.”

While the jury is still out on whether or not this firmware update will actually fix what is a terrible physical chassis design, one thing remains true: DON’T buy you ram or internal storage from apple. They charge a ridiculous markup for it. Buy the fastest CPU machine you can, with the minimum ram and storage configuration, then buy your ram and ssd from a third party vendor such as OWC. You’ll save a ton of money.


Your advice is sadly very out of date.

Ram upgrades are currently only an option for the Mac Pro (trashcan), the 27" iMac, and (possible but not easy as you have to take the entire thing apart) the iMac Pro. Every other model of Mac now has soldered in place RAM.

The only Macs that still use SATA storage are the non-pro iMacs and the Mac Mini. AFAIK, every other Mac now uses proprietary pci-e SSD sticks. On the latest Macbook Pros, IIRC, the SSD is soldered onto the logic board (so data recovery from a dead system becomes a problem).

Basically, nowadays the smartest thing to do in most cases is to order your mac with the RAM and storage you will need for the life of the system. Especially if upgrading will require major disassembly - risking destroying your $2000+ computer in an attempt to save a few hundred bucks on an upgrade makes no sense at all.


I was about to say! Here’s the iFixit analysis of the (latest) MacBook Pro, which says as much.

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wow, thanks for the update. I have a trashcan at work, just upgraded its ram with a kit from OWC to max it out. last macbook I bought for myself was the 17" just after they discontinued it, which I also maxed out, and is still running very strong. another nail in the mac coffin as far as I’m concerned. my next purchase will be a new desktop workstation for home, unless apple wows me with their alleged mac pro release aka the cuperino sasquatch, I’m buying a pc. sighs

As I expressly linked in the article, the fix was tested and does, indeed, correct the issue, in large part due to actually turning up the fans when the device gets warm. Probably a good idea. :wink:

More over RAM prices are absurd right now. Like in excess of the markup apple usually applies. So even if you could upgrade the RAM buying from apple could very well be a wash.

Yes. Especially those made by Apple.

On most apples, installation is rather difficult.

The trackpad can be replaced without removing the battery.
The processor, RAM, and flash memory are soldered to the logic board. Repairs and upgrades will be impractical at best.
The top case assembly, which includes the keyboard, battery, and speakers, is firmly glued in place—making all those components hard to replace separately.
The Touch ID sensor doubles as the power switch, and is paired with the T2 chip on the logic board. Fixing a broken power switch may require help from Apple, or a new logic board.

yes, you can put more ram in a 27 inch (non pro) imac, but you can’t easily replace the storage.

The 2015 macbook pro had soldered ram, but you could replace the (non standard) nvme ssd drive.

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