32bit Linux, 64bit CPU, and 4 gigs of ram

[Red Squirrel]

If I have a 32bit version of Linux installed on a machine with a 64bit cpu and 4 gigs of ram or more, will it see all the ram, or will it still be limited at 3.5? I know this is the case with Windows, just not sure if it is with Linux. I have 3.5 in my server, thinking of making that 4.

 

[Nothinman]

Depends on whether the kernel was configured with HIGHMEM64G enabled or not. But I really don't see a reason to use a 32-bit kernel anyway unless you're stuck with some crappy hardware that doesn't have OSS drivers.

 

[Red Squirrel]

Just never bothered upgrading the OS when upgraded the hardware. It's a huge process to rebuild that server so I'll only do it if theres a really huge reason to.

 

[Nothinman]

Installing a 64-bit kernel is a simple as installing another package, there's nothing else that you would need to change.

 

[Tarrant64]

Originally posted by: Nothinman
Installing a 64-bit kernel is a simple as installing another package, there's nothing else that you would need to change.

Best thing about using Linux. :thumbsup:

 

[Red Squirrel]

Really? I don't need to get an actual 64bit version of my distro and reformat? What about a full distro upgrade, like going from FC5 to FC7?

 

[Nothinman]

Debian prepackages amd64 kernels in their i386 distribution so there's no harm in trying, I'm not sure about other distros. The only thing that would be 64-bit would be the kernel in the case I'm talking about, but since I really doubt you need a 32-bit /bin/ls and all having a 64-bit version gets you is slightly more disk and memory usage I wouldn't worry about it.

I really doubt you can directly upgrade FC5->FC7, you might be able to do FC5->FC6->FC7 but I haven't had any real experience with FC in long enough to really know how painful that'll be.

 

[Peter]

In a 64-bit distro, /everything/ is compiled to 64-bit code, except maybe a few things that aren't ready for that yet.

So yes, it's a full reinstall if you want to do it right.

OP: There isn't really much point in asking the same question over and over and over.

The answer always is:

* 32-bit mode is HARDWARE LIMITED to four gigabytes of total SPACE, not all of which is available to RAM.
* There is a (rather poorly performing) paged 36-bit extension to this, called PAE.
* If you want fast AND big, you need 64-bit linear mode.

 

[Nothinman]

So yes, it's a full reinstall if you want to do it right.

Doing it right is subjective. Most of the time a full 64-bit distro is pointless and just ends up wasting memory and disk space so installing a 32-bit distro and then a 64-bit kernel on top of it will be optimal.

* 32-bit mode is HARDWARE LIMITED to four gigabytes of total SPACE, not all of which is available to RAM.

The only 4G limit is for virtual address space, you can have up to 64G of memory as long as the hardware can handle it and the OS fully supports PAE.

PAE just enables another level of page tables, it's not inherently any slower. Apps attempting to use more than their 3G of VM will be a little bit slower because they'll be constantly remapping addresses but otherwise they perform almost exactly the same.

 

[fyleow]

..

 

[Nothinman]

Sure you need 64-bit drivers but just about every driver is included with the kernel. nVidia and ATI both provide 64-bit drivers for their non-free stuff so that's not an issue either.

 

[Fox5]

There's no 64 bit flash binary (as well as a few other linux apps) so there is a bit of an inconvenience of going with 64 bit.
Plus, the 64 bit stuff tends not to be as developed as the 32 bit stuff and thus poorer performing.

As always, go 64 bit only for the tangible benefits, not because you can. Using over 3.5GB of ram happens to be one of the main tangible benefits of 64 bit.