I recently got a computer and assuming it was 32-bit, installed fedora 13 for i686. But after looking at /proc/cpuinfo, I noticed that the cpu has the lm flag and I believe this means I have a 64 bit processor.

This leads me to a few questions:
1. Do I definitely have a 64 bit processor of does this just mean 64 bit "compatible"?
2. Should I install the x86_64 version instead?
3. Does doing so make any real difference?

I've read how some programs/features aren't fully supported in the x86_64 version (flash?) and don't really feel like fighting to get things to work that are working just fine now under i686. That is of course unless there's a good reason to do so. Do any such problems exist, or have the most recent releases pretty much overcome any problems.

Just to let you know, I'm using this machine as my home PC and use it for browsing, watching movies, listening to music and maybe some light programming.

--thanks

Post your /proc/cpuinfo if in doubt. uname -p should inform you about 32/64.

Presuming it's a 64 bit cpu, if you want to unleash the power you bought, take the (lessening) pain and go 64 bit. As things stand, you cannot avail of many optimisations available on 64 bit cpus, and you will not get 64 bit drivers. You will not address over 3 gig. You _will_ have megabytes of bug fixes for the dodgiest chipsets ever made, which you don't need :-/.

What would "just 64 bit compatible" mean?
Anyway, the lm means you have a 64 bit processor.

Maybe. Some programs run noticeably faster in 64 bit mode. Some run faster in 32 bit. If you really cared about the programs that run faster in 32 bit mode, you can install and run those in 32 bit mode even in a 64 bit OS (but you can't run any 64 bit mode programs in a 32 bit OS). But generally, no one bothers to identify those programs that run faster in 32 bit mode.

Probably not.

Some people will say the amount of ram you have should heavily influence your decision. If you have more than 8GB, I'd agree that suggests you choose 64 bit. If you have less than 1GB, I think that suggests you stick with 32 bit.

But for typical ram sizes in between, I don't think ram size should influence your choice. 64 bit is no more appropriate at 6GB of ram than it is at 2GB. Even at 1GB, 64 bit is OK and at 8GB, 32 bit is OK. (for three point something GB of ram through 8GB or higher, 32 bit PAE is fine).

You seem to be using Fedora. For the few programs that don't work in 64 bit mode (or any you decide you prefer in 32 bit mode for performance or other reasons), I've found Mepis moderately inconvenient for installing 32 bit versions of programs on a 64 bit system. I think that would be consistent across Debian based distributions. Centos (yum) makes it noticeably easier for the user to arbitrarily select a 32 bit version of any package. I assume (but don't know from direct experience) that Fedora would also make it easy to install a 32 bit package if you decided for any reason that you preferred it.

32 bit application programs seem to run as well or even a tiny bit better on 64 bit OS's than they do on 32 bit OS's (unless you're seriously short of ram, in which case 32 bit programs would run much better on a 32 bit OS).

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heres /proc/cpuinfo. I'm only posting the first processor because the other 3 are identical:

and uname -p gives i686. Also, I have 3.2GB of ram.

Unlikely. Probably you have 4GB of ram. If your BIOS supports a full 4GB (and its settings are correct) then either a 32 bit PAE kernel or a 64 bit kernel will let you use very nearly the full 4GB.

If you now can use only 3.2GB, either your BIOS settings are wrong, or you have a non PAE 32 bit kernel.

You can switch from 32 bit non PAE to 32 bit PAE changing only the kernel, leaving the rest of the software unchanged. Switching to a 64 bit kernel would require reinstalling the whole system.

I just checked out the bios settings, and it detects 4GB of memory. Wonders never cease.

To enable PAE, I see there's a yum package kernel-PAE.i686. I may try installing this to handle the ram issue. As for the 32/64 bit OS question, I think I'll give it a shot this weekend if I can get some time.

I have a 64-bit machine at work running fedora and I seem to recall about a year ago having to install the 32-bit version of a package for some reason. I don't remember the details, but the installation was trivial. I just had to enable the repo and used yum to install the package. No sweat really.

Almost any BIOS will detect and report 4GB (if that is what you have installed) even if some other BIOS setting prevents the BIOS from letting the OS use the full 4GB, in fact even if the design of the motherboard totally prevents use of the full 4GB.

In other threads, I described how to check dmesg output to see whether your BIOS allows your OS to use the full 4GB. That might be worth doing before installing the PAE package. (But you might equally well install PAE and see if it enables more ram and only look at dmesg to help diagnose things if PAE doesn't enable more ram).

I think that you would need to have much more than 4 gig to make any use of a 64 bit OS. It will take more overhead ram and disk space so even if you near 4 gig there would be little to no benefit.

There is always overhead ram being used on all x86 systems. You may be able to reduce some of the cached bios or video to return a bit but expect 600 m to 1 G being used. You can't expect that all 4 gig would be available to the OS.

Can you get me a transmission mount for a Suzuki Carry DB51t?

I have a 64 bit box w/4Gig, and it's actually plenty. I have X, xfce, and run many complex compiles, and never saw over 2.5 gig used.

A 64 bit OS will use more ram and more disk space for the same work than a 32 bit OS would. That is true regardless of how much ram or disk space you have. But the effect is not proportional to total space. If you have a lot of ram and disk, the amount extra needed for a 64 bit OS doesn't matter much. Even with significantly less than 4GB of ram, the extra needed by a 64 bit OS is a small enough fraction that you shouldn't worry about it.

The typical advantages of a 64 bit OS have nothing to do with ram size. 64 bit uses SSE floating point by default, while 32 bit normally uses legacy floating point. So many programs that run faster because of SSE will run faster apparently because of 64 bit. 64 bit also has twice as many registers as 32 bit mode. GCC is particularly bad at dealing with the shortage of registers in 32 bit x86. So many programs will be faster in 64 bit mode because gcc generates better code for them.

Those advantages (and some others) trade off against the extra ram and disk use of a 64 bit OS, plus the extra L2 cache misses that are a consequence of some of that extra ram use. The net benefit of 64 bit mode is hard to predict and usually small.

Most motherboard graphics systems take a significant chunk of your ram. Other than that, most of the overhead is address space rather than ram, so with correct BIOS setting and either PAE or 64 bit mode, you can use far more than 3.2GB of your 4GB of ram even with motherboard graphics, and if you don't use motherboard graphics you can use almost all of 4GB of ram.

If you don't need any 32-bit programs or can replace them or find workarounds, I would install 64-bit. johnsfine is right in that programs are slightly larger and use slightly more RAM, but you will not notice it, because it's only a bit more. Also, with many programs you will get a performance boost, especially in multimedia and scientific programs, but in other programs as well. The more RAM you have, the more you should think about switching, because the benefits increase the more RAM you have.

Some people think they are going newer or better with a 64 bit OS. Two issues only affect a decision. One is ram. If you don't have more than 4 gig NO 64 bit OS will help that. Only if you have more than 4 Gig will you be able to consider a 64 bit OS.

Second is applications. It is still a 32 bit world out there. It is much easier to live in it. Unless you have one or more 64 bit only application(s) should you consider the 64 bit OS.

This is the chrome on the engine feeling. You can put all the chrome you want on an engine but it won't make it faster.

But if I put flame decals on my case, it'll make the cpu faster, right?

I can vouch for this, it does seem to increase the speed of everything (even if only in your head)

This is a complicated (but not necessarily important) decision. I wonder if ordinary Linux users reading this stuff can distinguish the useful posts from:

I'm not able to even consider 64 bit if I have 4GB or less?? So when I ran 64 bit Centos on a 3GB system and ran 64 bit Mepis on a 2GB system, maybe I was dreaming it all.

While jefro's statement doesn't explicitly say 32 bit is better than 64 bit for a 3GB system, it certainly implies that. It even implies 64 bit might be better than 32bit PAE for a 5GB system. Is there supposed to be some underlying technical explanation for that. What is the difference between 3GB and 5GB of physical ram that is supposed to influence the relative benefits of a 32 bit OS vs. a 64 bit OS? All the people who keep describing memory size around 4GB as an important boundary for that choice seem to just say it. I've never seen the reason explained.

No single 32 bit process can use more than 3GB of ram at a time. That may seem like a relevant restriction in a 5GB system, but in practice it isn't. You have multiple processes, plus file caching, plus the kernel all consuming parts of your total ram. That could easily add up to a lot more than 5GB while each process uses a lot less than 3GB.

When I ran 32 bit Centos on an old computer with 8GB (not 64 bit capable), I frequently pushed the limits of 8GB physical and used quite a lot of swap, while very rarely hitting the limit of 3GB virtual per process.

A 64 bit only application?? I don't recall ever seeing one of those. I certainly never ran one of those on any of the computers where I have a 64 bit OS and significant confidence that a 64 bit OS was the right choice (vs. 32 bit).

I've seen 64 bit only uses of applications, meaning an application available in both 32 bit and 64 bit used to solve a problem that is so big that the 32 bit version would fail due to lack of virtual memory (even when running on a 64 bit OS and getting a full 4GB). In my work, such problems are only infrequent. But in general use of Linux, such problems are so rare they don't even belong in a general discussion of the choice between a 32 bit and 64 bit OS.

32 bit only applications (not 64 bit only applications) belong in a discussion of 32 bit vs. 64 bit OS's. There are enough 32 bit only applications that the topic deserves some mention. Once you get them properly installed, 32-bit only applications should run better in a 64 bit OS than they do in a 32 bit OS. But they may be significantly harder to install in a 64 bit OS and that may be a reason to choose a 32 bit OS instead.