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Mac Architecture Questions

Hi everyone :) am a newbie to develop applications for Mac. My questions are regading to different OS architectures in Mac and am greatly confused in this. Kindly bear with me if my questions are very cheap. Thank u all:)

  1. I know that there is 32 bit support for 10.6(SnowLeopard). I would like to know if there is 32 bit support for 10.7(Lion)??

  2. I have a 64 bit machine. I want a 32 bit 10.7 on it. How would i do so??

  3. I have a 32 bit iMac and I have 10.6.8 in it. I have built an application on it; the application uses a user developed library which is also 32 bit. Now I carry on this application to another Mac machine which has 64 bit processor with 10.7(Lion). Will I be able to execute the same application as such in 10.7(Lion)?? I was not able to do so.

Solution

    1. OS X uses a binary format that can support multiple architectures (e.g. 32- and 64-bit Intel, as well as PowerPC, etc) in a single executable or library. Most of the binaries and libraries in Lion are dual-architecture 32&64-bit Intel. So, yes, there is 32-bit support in Lion.

    2. There is no such thing as 32-bit Lion; it's a dual-architecture OS. It can boot the kernel in either 32- or 64-bit mode, and run programs in 32- or 64-bit mode. Unlike most other OSes, it can even run programs in 64-bit mode under a 32-bit kernel. Whenever you run a program in Lion, it checks what architectures the program includes and what the CPU is capable of, and picks the "best" mode to run that program in.

    3. There's no obvious reason this shouldn't work. If you were trying to use a 32-bit-only library from a program that was running in 64-bit mode, or a 64-bit-only library from a program running in 32-bit, it would fail. But if the program is 32-bit only it'll obviously run in that mode, your user developed library is 32-bit, and all of the libraries supplied with the OS are 32+64-bit.

      There are a few things that might cause your 32-bit program to fail under Lion. First, does it depend on any libraries other than the one you mentioned and those supplied with the OS (e.g. libraries compiled locally by something like MacPorts, Fink, or Homebrew)? If so, those libraries might've been compiled 64-bit only. IMO libraries should always be compiled for all relevant architectures to avoid this sort of problem, but that's not the default.

      Another possible source of trouble is if your program isn't really a program, but something that loads into another program (e.g. a plugin of some sort, screensaver, etc). In that case, your plugin needs to support whatever mode the program that'll load it is running in. You can actually get this issue with Java programs, since the java runtime will start in 64-bit mode (when the CPU supports it) in Lion.

      Telling us more about your program and what specific error you get would probably help a lot...