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Does usb-c spec break backward compatibility ?, a 2018 macbook work perfectly fine with 2025 usb c charger

techpression 1y ago
I don’t know if it’s the spec or just a plethora of vendors that ignores it, but I have many things with a USB-C port that requires USB-A as source. USB-C to A to C works, yay dongles, but not just C to C. So maybe it’s not really breaking backwards compatibility, just a weird mix of a port and the communication being separate standards.
- mrheosuper 1y ago
  because those usb-c ports do not follow the spec. If they had followed the spec from 1st day there would be no problem even now.
- fragmede 1y ago
  it's vendors just changing the physical port but not updating the electronics. specifically, a 5.1kΩ pull-up resistors on the CC1 and/or CC pins is needed on the host (was usb-a) side in order for the c to c cable to work.
danielheath 1y ago
Some things don't work unless you use the right kind of USB-C cable. EG your GPU and monitor both have a USB-C port. Plug them together with the right USB cable and you'll get images displayed. Plug them together with the wrong USB cable and you won't. USB 3 didn't have this issue - every cable worked with every port.
- mrheosuper 1y ago
  That is not backward compatible problem. If a cable that does 100w charging when using pd2.0, but only 60w when using with pd3.1 device, then i would agree with you.
  - yoz-y 1y ago
    The problem is not backward compatibility but labeling. A USB-C cable looks universal but isn’t. Some of them just charge, some do data, some do PD, some give you access to high speed. But there is no way to know. I believe the problem here is that you will have PNG images that “look” like you can open them but can’t.
    - mrheosuper 1y ago
      the parent said "changing the compression algorithm will break backwards compatibility", which i assume is something works now won't work in the future. The usb-c spec is intentionally trying to avoid that.
      - danielheath 1y ago
        Today, I can save a PNG file off a random website and then open it. If PNG gets extended, it's entirely plausible that someone will view a PNG in their browser, save it, and then not be able to open the file they just saved. There are those who claim "backwards compatibility" doesn't cover "how you use it" - but roughly none of the people who now have to deal with broken software care about such semantic arguments. It used to work, and now it doesn't.
        johnisgood 1y ago
        This is what I fear, too. Do they mention which C libraries use this spec?
        mrheosuper 1y ago
        which is what usb-c spec has been avoiding so far. Even in USB4 spec, there are a lot of mentioning the new spec should be compatible with TB3 devices. USB-C spec is anything but breaking backward compatible.
        fc417fc802 1y ago
        The alternative is the website operator who wants to save on bandwidth instead adopts JXL or WEBP or what have you and ... the end user with old software still can't open it. It's a dichotomy. Either the provider accommodates users with older software or not. The file extension or internal headers don't change that reality. Another example, new versions of PDF can adopt all the bells and whistles in the world but I will still be saving anything intended to be long lived as 1/a which means I don't get to use any of those features.
mystifyingpoi 1y ago
Yeah, I also don't think they've broken backwards compat ever. Super high end charger from 2024 can charge old equipment from 2014 just fine with regular 5V. What was broken was the promise of a "single cable to rule them all", partly due to manufacturers ignoring the requirements of USB-C (missing resistors or PD chips to negotiate voltages, requiring workarounds with A-to-C adapters), and a myriad of optional stuff, that might be supported or not, without a clear way to indicate it.
deleted 1y ago
[deleted]
zirgs 1y ago
Yeah - it's a mess. Some devices only charge with a charger that supports PD. Some other devices need a charger WITHOUT PD support.
- mrheosuper 1y ago
  If those devices follow the spec, they dont need charger without PD support. You don't follow spec, you're on your own.
  - zirgs 1y ago
    Yes, but, unfortunately - devices like that exist.

I don’t know if it’s the spec or just a plethora of vendors that ignores it, but I have many things with a USB-C port that requires USB-A as source. USB-C to A to C works, yay dongles, but not just C to C. So maybe it’s not really breaking backwards compatibility, just a weird mix of a port and the communication being separate standards.

mrheosuper 1y ago
because those usb-c ports do not follow the spec. If they had followed the spec from 1st day there would be no problem even now.
fragmede 1y ago
it's vendors just changing the physical port but not updating the electronics. specifically, a 5.1kΩ pull-up resistors on the CC1 and/or CC pins is needed on the host (was usb-a) side in order for the c to c cable to work.

danielheath 1y ago

Some things don't work unless you use the right kind of USB-C cable. EG your GPU and monitor both have a USB-C port. Plug them together with the right USB cable and you'll get images displayed. Plug them together with the wrong USB cable and you won't. USB 3 didn't have this issue - every cable worked with every port.

mrheosuper 1y ago
That is not backward compatible problem. If a cable that does 100w charging when using pd2.0, but only 60w when using with pd3.1 device, then i would agree with you.
- yoz-y 1y ago
  The problem is not backward compatibility but labeling. A USB-C cable looks universal but isn’t. Some of them just charge, some do data, some do PD, some give you access to high speed. But there is no way to know. I believe the problem here is that you will have PNG images that “look” like you can open them but can’t.
  - mrheosuper 1y ago
    the parent said "changing the compression algorithm will break backwards compatibility", which i assume is something works now won't work in the future. The usb-c spec is intentionally trying to avoid that.
    - danielheath 1y ago
      Today, I can save a PNG file off a random website and then open it. If PNG gets extended, it's entirely plausible that someone will view a PNG in their browser, save it, and then not be able to open the file they just saved. There are those who claim "backwards compatibility" doesn't cover "how you use it" - but roughly none of the people who now have to deal with broken software care about such semantic arguments. It used to work, and now it doesn't.
      - johnisgood 1y ago
        This is what I fear, too. Do they mention which C libraries use this spec?
      - mrheosuper 1y ago
        which is what usb-c spec has been avoiding so far. Even in USB4 spec, there are a lot of mentioning the new spec should be compatible with TB3 devices. USB-C spec is anything but breaking backward compatible.
      - fc417fc802 1y ago
        The alternative is the website operator who wants to save on bandwidth instead adopts JXL or WEBP or what have you and ... the end user with old software still can't open it. It's a dichotomy. Either the provider accommodates users with older software or not. The file extension or internal headers don't change that reality. Another example, new versions of PDF can adopt all the bells and whistles in the world but I will still be saving anything intended to be long lived as 1/a which means I don't get to use any of those features.

mystifyingpoi 1y ago

Yeah, I also don't think they've broken backwards compat ever. Super high end charger from 2024 can charge old equipment from 2014 just fine with regular 5V. What was broken was the promise of a "single cable to rule them all", partly due to manufacturers ignoring the requirements of USB-C (missing resistors or PD chips to negotiate voltages, requiring workarounds with A-to-C adapters), and a myriad of optional stuff, that might be supported or not, without a clear way to indicate it.

deleted 1y ago

[deleted]

zirgs 1y ago

Yeah - it's a mess. Some devices only charge with a charger that supports PD. Some other devices need a charger WITHOUT PD support.

mrheosuper 1y ago
If those devices follow the spec, they dont need charger without PD support. You don't follow spec, you're on your own.
- zirgs 1y ago
  Yes, but, unfortunately - devices like that exist.