Fedora core 3 - 4GB memory limit?

[Matt Roth]

 >> 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.

Eric,

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