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Old 11-27-2012, 09:59 PM   #1
cissp18
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Physical RAM support for Fedora 17


Hello all,

I want to know how much RAM is supported by Fedora 17 desktop OS.

Regards.
 
Old 11-27-2012, 10:11 PM   #2
sag47
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It depends on the version you download. If you download the 32 bit version (i386, i686, etc) then 4GB RAM (2^32 addressable space). If you download the 64bit version (e.g. x86_64) then it supports 6004799503160661GB RAM (2^64 addressable space); more than you can fit in a modern desktop. The 4GB support in the 32bit is with a PAE Linux Kernel.

Why do you ask? Is there something in particular you're looking to do and have performance concerns? Please elaborate.

SAM

**********EDIT

CORRECTION: You're limited by the x86_64 implementation of the Linux kernel. Most information I stated above is INCORRECT. Currently the Linux Kernel only supports 2^46 bits of memory (64TB of RAM). Fedora 17 uses the 3.X kernel so it has the same limitations.

Here's a better breakdown for Fedora (and most modern GNU/Linux distros) memory support...
Code:
Fedora 17 max memory sizes
+----------------------+---------------------------------+
| Linux Kernel         | Maximum Physical RAM            |
|----------------------+---------------------------------+
| 3.7 x86 32-bit       | 4GB (2^32 bits direct mapping)  |
| 3.7 i386 32-bit PAE  | 64GB (page-frame structure)     |
| 3.7 x86_64 64-bit    | 64TB (2^46 bits direct mapping) |
+----------------------+---------------------------------+

Notes:
* There's a difference between i386 and i386 PAE.  If a download just says 
  i386 it does not necessarily have PAE support enabled.
* 32-bit PAE kernel recommends no more than 8GB RAM for performance reasons.
* Fedora 17 comes with i686 rather than i386 but for your purposes it's the
  same thing.  It just has to do with the architecture conformance for the 
  processor.
* i386/i486/i586/i686 have the same instruction set architecture (ISA) for
  IA-32.  The changes between them involve internal logic and accessible
  registers.  Hence, why you can treat them the exact same.
Kernel Documentation references
So a general rule of thumb for you should be if you have more than 4GB of RAM and your processor is 64bit capable then just go with the x86_64 compiled kernel for performance and memory support.

Last edited by sag47; 11-27-2012 at 11:42 PM.
 
Old 11-28-2012, 01:40 AM   #3
Weapon S
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Quote:
Currently the Linux Kernel only supports 2^46 bits of memory
Currently (most?) processors only support 46-bits memory space. It seems OP had a very specific question, so I'll shut up now >_>
 
Old 11-28-2012, 05:53 AM   #4
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The above posts seem to be blurring the important distinction between the limit on physical ram per system and the limit on user mode virtual address space per process. I expect the OP is asking about the former, but I'm not sure.

Regarding physical ram per system for 32-bit without PAE. The amount is determined by BIOS and motherboard details. It is typically around 3.25GB and is always less than 4GB.

Regarding 32-bit with PAE, sag47 linked to a page that said
Quote:
The i386 arch, under some circumstances, will permit you to stick up to 64GiB of RAM into your 32-bit machine.
Then pasted in a table indicating 64GiB is supported. I don't believe that is correct.

The x86 32-bit architecture supports 64GiB with PAE, but I believe Linux currently does not. RHEL 4 had a (kernel build time optional) ugly kludge to support 64GiB. But later RHEL (and so far as I understand later kernels in other distributions) didn't have that option. Without that kludge, PAE physical ram is limited to 16GiB and even that much might be unsound depending on usage.

The x86-64 architecture supports 48-bits (not 64) of virtual address space per process, designed to be split as 47 bits of user mode and 47 bits of kernel. I wasn't aware of a lower Linux limit on that, but I might have missed something.

Each x86-64 CPU model has its own limit on the number of bits in a physical address. For example, the old AMD chip in my system has a 40 bit limit. I expect newer chips have hgher limits. I'm not aware of a Linux limit lower than the chip's limit, but I'm not sure.
 
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Old 11-28-2012, 11:44 AM   #5
cissp18
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Hello everybody,

Thank you for the prompt response.

I am going to install Fedora-17-x86_64-Live-Desktop on my Intel I3 540 3.07GHz processor based desktop. I have been having some issues with Windows with 12 GB of RAM so I wanted to make sure that I don't have issues with Fedora with 12 GB RAM.

Regards.
 
Old 11-28-2012, 12:31 PM   #6
johnsfine
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Quote:
Originally Posted by cissp18 View Post
I have been having some issues with Windows with 12 GB of RAM so I wanted to make sure that I don't have issues with Fedora with 12 GB RAM.
"Issues" is too vague for us to guess whether you are having hardware problems or operator error or misunderstanding the expected behavior or hitting basic limits of 32-bit Windows, or what.

So I can't predict whether you will have "issues" with Fedora with 12GB.

But we can assure you any such issues are not inherent in Fedora. x86_64 Fedora can handle 12GB without coming anywhere near any relevant limits.
 
Old 11-29-2012, 10:46 AM   #7
cissp18
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This is not a forum/place to mention about issue/s related to Windows but the previous comment in response to my initial query has some doubts because of "issues" not issue.


i said "Issues" because:

1. After adding 4 GB of RAM to the existing 8 GB RAM in my system I see that Windows 7 becomes extremely slow.
2. The system sometimes starts to freeze then respond.

I am using Windows Ultimate 7 64 bit.

I hope the above details help.

Regards.
 
Old 11-29-2012, 11:21 AM   #8
johnsfine
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I don't know what else we could expect you to know/describe. But what you have described is not enough to get much insight into the underlying problem.

If it is a hardware problem, changing from Windows to Linux probably won't help.

Beyond that, the possibilities are too diverse for helpful speculation.

Try Fedora and see.
 
Old 11-29-2012, 03:15 PM   #9
cissp18
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I don't see any issue with the hardware as I have used many other tools and earlier versions of winodws and my system works just fine until the additional RAM is added. I will see how it goes with Fedora.

Thank you everyone for your inputs.

Regards.
 
Old 11-29-2012, 08:56 PM   #10
remusrm
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the issue might be bad ram, or ram that has lower speed then what you have, or vice versa
 
Old 11-29-2012, 09:01 PM   #11
TobiSGD
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Quote:
Originally Posted by cissp18 View Post
I don't see any issue with the hardware
Of course you do. You add an additional piece of hardware to the machine and suddenly the machine becomes slow. Why do you think that this can't be a hardware issue?
I would recommend to do a run of Memtest86+ to rule out issues with the RAM.
 
Old 11-30-2012, 05:17 PM   #12
cissp18
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The speed of the RAM is not slow because I swapped the older RAM with the new one and system was working fine.

I will test 12 GB RAM with windows server and Fedora and see how it goes.
 
Old 11-30-2012, 08:01 PM   #13
jefro
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You test ram with tools like memtest, windows memory diagnostics, bios information and maybe even some system information apps.

Usually you put in more ram and it goes faster. This assumes your motherboard supports the ram, OS supports the ram, bios has been set to match ram, you put in the correct ram and the ram has been approved for use in that board and existing ram.
 
Old 12-06-2012, 04:37 PM   #14
westzilla
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Quote:
Originally Posted by jefro View Post
You test ram with tools like memtest, windows memory diagnostics, bios information and maybe even some system information apps.

Usually you put in more ram and it goes faster. This assumes your motherboard supports the ram, OS supports the ram, bios has been set to match ram, you put in the correct ram and the ram has been approved for use in that board and existing ram.
eww windows yuck. if I were to guess id say its a bad RAM stick id try swapping out with a new one
 
Old 12-08-2012, 11:52 AM   #15
cissp18
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It works just fine with Fedora Spin Security. I believe its something wrong with the windows image that I had installed.

Today I tested 12 gig RAM with Fedora and everything went just fine.

Regards.
 
  


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