Re: Fedora core 3 - 4GB memory limit?

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>> Eric Persson wrote:
>> Hi,
>> I have a Fedora core 3 machine:
>> Fedora Core release 3 (Heidelberg)
>> Linux localhost.localdomain 2.6.9-1.667smp #1 SMP Tue Nov 2 14:59:52 EST
>> 2004 i686 i686 i386 GNU/Linux
>> It currently have 3gb of memory in it, and I have two spare slots which
>> I intend to fill with an additional 2gb of memory to get to a total of
>> 5gb in the machine.
>> Is this possible or is there a 4gb limit in the kernel, which would make
>> something like PAE needed. If so, is that already included in the stock
>> kernel used?
>> Any other apparent caveats?
> Alexander Dalloz wrote:
> Does your motherboard support such an amount of RAM? You did not tell us
> which one you run. You should look into the manual. On non server i386
> x86 boards the amount of RAM is often limited to max. 4 GB, where you
> even loose the amount which is required by I/O components. Thus you
> often only have max. 3.5GB RAM even if 4GB modules sticked in.


In addition to Alexander's points, there are a few other things to consider when installing more than 4 GB of RAM:

1) 32-bit processors (without 64-bit extensions, such as Intel EM64T) are limited to 4 GB of physical memory.

2) 32-bit operating systems and applications use 32-bit pointers than can only address up to 4 GB of physical memory.

3) 32-bit hardware (such as PCI ethernet cards) can be problematic. I have a Level 5 Networks EtherFabric EF1-21022T that required a custom driver for our system. I believe it was a DMA bounce buffering issue.

If you don't have a 64-bit processor or a processor with 64-bit extensions, you are limited to 4 GB of RAM. Since according to your post you are running Fedora Core 3 i386, this is the most likely scenario.

If you do have a 64-bit processor (and assuming you want to keep running Core 3), I believe you'll need to install Fedora Core 3 x86_64. This will give you the 64-bit OS and applications needed to take advantage of the additional memory.

Finally, if you decide to upgrade from 32-bit to 64-bit, evaluate the hardware in the system beforehand to insure it will make the transition smoothly. Hardware that is labeled as having a 64-bit interface should be fine, but I'd recommend doing some compatibility research on anything labeled as 32-bit before making the change.

To give you an idea of where I'm coming from, my 64-bit architecture consists of a Dell PowerEdge 6850 with 4 Intel Xeon processors and 20 GB of physical memory running Fedora Core 3 x86_64. That said, I am by no means an expert on the differences between 32-bit and 64-bit architectures. I hope this post was helpful, but if I have made any factual errors please post corrections back to the list.

Thank you,

Matthew Roth
InterMedia Marketing Solutions
Software Engineer and Systems Developer

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