I have 2 identical system with 32 GB of ram and when I was using the PAE kernel it was displaying 27 GB of ram. I was told that I needed to install the 64bit OS in order to see the 32 GB of ram. I loaded the 64 bit RHEL 5 OS and it still showed 27GB of ram. That is when the RH people mentioned that the systems was using some of the 32 GB of memory.
:) -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Hugh Brown Sent: Wednesday, September 24, 2008 7:33 AM To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list Subject: Re: [rhelv5-list] PAE Kernel 32 bit RHEL 5.2 64GB RAM My understanding was that it was an addressing limitation. The processor can only address 32-bits worth of hardware and the addresses for memory and pci devices are in the same pool. Way back when, it was decided that devices would be addressed starting at the 2^32 boundary and work backward. Memory got addressed from the low boundary and worked up. When machines finally got 4gb of memory the two met and a portion of memory/ram couldn't be addressed. Hugh solarflow99 wrote: > thats interesting, I never came across that before. I dont know why it > needs to map ram like that, and not just use the video card ram. That means > if I had a 4GB video card there would be nothing left for me? :) > > > > > On Wed, Sep 24, 2008 at 3:07 PM, Sharpe, Sam J <[EMAIL PROTECTED]>wrote: > >> Because both have different PCI devices? >> >> I think Janne's point is that: >> >> Machine 1: 4096 - 3986 = 110 MB of memory mapped to PCI devices and >> unavailable to the OS >> Machine 2: 4096 - 3286 = 810 MB of memory mapped to PCI devices and >> unavailable to the OS >> >> You don't have Graphics Cards with a total of something like 768MB of >> Memory installed in Machine 2 do you? Of course if the machines are >> completely identical, then I have no idea. >> >>> -----Original Message----- >>> From: [EMAIL PROTECTED] [mailto:rhelv5-list- >>> [EMAIL PROTECTED] On Behalf Of solarflow99 >>> Sent: 24 September 2008 15:02 >>> To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list >>> Subject: Re: [rhelv5-list] PAE Kernel 32 bit RHEL 5.2 64GB RAM >>> >>> but why does 1 system show 3.2GB and the other 3.9? they both had 4GB >>> installed >>> >>> >>> >>> On Wed, Sep 24, 2008 at 2:59 PM, Janne Blomqvist >> <[EMAIL PROTECTED]> >>> wrote: >>> >>> >>> solarflow99 wrote: >>> >>> >>> that makes me wonder about something I have several >> computers >>> with 4GB of ram using the regular 32 bit kernel (non-PAE) and I see >>> different amounts of ram, for instance: >>> ]# free -m >>> total Mem: 3286 >> ]# >>> free -m >>> total Mem: 3986 >>> >>> >>> >>> Probably PCI device memory. They start at 4 GB and go downwards >>> (AFAIK most are not capable of 64-bit addressing so they have to be >> below >>> 4 GB). >>> >>> Now, many BIOS:es support "PCI hole remapping" (or whatever it's >>> called), meaning that the memory that gets clobbered by the PCI >> devices >>> can be remapped to somewhere beyond the 4 GB limit. However, obviously >>> you'll need PAE or x86-64 in order to access this remapped memory. >>> >>> -- >>> Janne Blomqvist _______________________________________________ rhelv5-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/rhelv5-list
