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Old 02-25-2009, 06:44 PM   #1
lemonlaw95
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switch from x86 to x86_64 without reinstalling?


i just installed fedora 9, but realized that i had installed the x86 version (it came on a dvd in linux format magazine). i didn't know that the "only-3gb-of-ram-for-x86" applied to linux, as my previous machines i used it on had under 3gb anyway.
so anyway, is there a way to switch to the x86_64 version without downloading and reinstalling it? kinda like ubuntu's distro upgrade (not sure if other distros have it?)

thanks in advance!

-lemon
 
Old 02-26-2009, 10:58 AM   #2
serafean
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Hi, don't know how ubuntu handles the distro upgrade process, but to my knowledge you can't change architectures without reinstalling.
Quote:
"only-3gb-of-ram-for-x86" applied to linux
It applies to all 32-bit systems, but most of them have "hacks" that overcome this. Use the highmem kernel I'm quite sure fedora provides, and you'll be able to use your whole 4GB of RAM.
 
Old 02-26-2009, 11:02 AM   #3
gergely89
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Technically a switch from x86 to x86_64 is not an upgrade, because all applications could be based on exactly the same source, only with different binaries built. For any upgrading programming the difference is about architectures and not content changes, when comparing x86 and x86_64 files. In the same way as you don't upgrade x86 packages with PowerPC equivalents.

If you have already some personal data in /home and the /home directory is located on it's own partition, then you can re-install the system with the x86_64 packages, by instructing the installer NOT to format the /home partition. If your home directory consists of text files, image files and other formats that do not care about architectures, then this should work. Binary executables stored in your home location are a different story.

I truly believe that you can not avoid a new installation. But maybe someone else has a better idea.

linux

Last edited by gergely89; 02-27-2009 at 11:04 PM.
 
Old 02-26-2009, 11:36 AM   #4
johnsfine
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Quote:
Originally Posted by lemonlaw95 View Post
i just installed fedora 9, but realized that i had installed the x86 version (it came on a dvd in linux format magazine). i didn't know that the "only-3gb-of-ram-for-x86" applied to linux,
It only applies to some kernel builds of 32bit Linux.

You can solve the problem by switching to a PAE kernel. I'm pretty sure there is a Fedora package you can install that is the PAE kernel.

Quote:
is there a way to switch to the x86_64 version without downloading and reinstalling it?
I'm nearly sure there is no way to switch to a 64bit kernel without a complete reinstall of the distribution.

I'm sure you can switch to a PAE kernel by changing only the kernel with no need to reinstall anything else.

If for some reason you can't install a package for a PAE kernel, the next alternative would be to install the various packages needed to do a kernel recompile and add the PAE support yourself. That still would be less disruptive (and less to download) than switching to a 64 bit kernel.

Quote:
Originally Posted by serafean View Post
most of them have "hacks" that overcome this.
PAE is not a "hack" it is an option in 32bit that makes a very clean change in the memory mapping data structure. A similar (but larger) change is non optional for 64bit mode (so the trivial "extra overhead" you might read about for PAE is a subset of the related extra overhead for the same aspect of 64bit mode, and even there is still trivial).

There is a much uglier hack (as a build-time kernel option) to provide more than 1GB kernel virtual memory in order to have room for data structures for a much larger amounts of ram (I think over 16GB). That version of the kernel should be avoided (use 64bit instead).

Last edited by johnsfine; 02-26-2009 at 11:47 AM.
 
Old 02-26-2009, 01:16 PM   #5
serafean
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Quote:
PAE is not a "hack" it is an option in 32bit that makes a very clean change in the memory mapping data structure.
Maybe I should have used the word "extension" (Physical Address Extension), sorry if that was misleading. I followed up, and found out that its a feature supported by CPUs, not only OSes. Always something to learn...
 
  


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