Date: Thu, 30 Aug 2007 14:58:38 -0700 From: "Michael K. Smith - Adhost" <mksmith@adhost.com> To: "User Bobby" <bobby@susanne.tomatoseed.org>, <freebsd-questions@freebsd.org> Subject: RE: 4gb address space limitation for i386 Message-ID: <17838240D9A5544AAA5FF95F8D52031602799BE0@ad-exh01.adhost.lan> In-Reply-To: <20070830172127.M11085@susanne.tomatoseed.org> References: <20070830172127.M11085@susanne.tomatoseed.org>
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Hello: > -----Original Message----- > From: owner-freebsd-questions@freebsd.org [mailto:owner-freebsd- > questions@freebsd.org] On Behalf Of User Bobby > Sent: Thursday, August 30, 2007 2:32 PM > To: freebsd-questions@freebsd.org > Subject: 4gb address space limitation for i386 >=20 > I have an IBM xSeries 350 4xPIII with 5.5gb of RAM, and see that only > about 3.5gb is being used under the i386 port. I've been looking > through the > archives to try and figure out what the root of the problem is and I > amn't > quite sure I know which part of the situation is the real problem. >=20 > Is it a limitation of the i386 port? That is to say, if there were a > specific PIII (i686?) port, would this problem be overcome? Or is it a > hardware limitation? Is it necessary to use a not-clean method to > access the extra address space (is this what PAE is?), and there's no > clean > way around it, regardless of the port? >=20 > I was looking at building a PAE kernel, but was discouraged by the lack > of > usb and certain SCSI support, both of which I'd really like to have (in > the case of SCSI, need to have). Is this lack of support because of an > inherent difficulty in the hardware, or could it be overcome in a > stable way with modification of the device driver code? >=20 > My basic (and very hypothetical) question - if I had unlimited time and > knowledge (I have limited both), what direction would I take to get > access > to all 5.5gb of RAM on this particular computer? >=20 > Thank you, > Bob You may just have one issue or you may have two. There is a 4 Gig limit to 32-bit Operating Systems (not just FreeBSD), so you either have to run a 64Bit system (which you can't) or fake it using PAE. You may also be running into the PCI-Hole which requires memory to map PCI devices. This can suck up anywhere to about 1/2 a Gig of RAM. PAE is definitely "at your own risk" and everything I've read about the potential ramifications (including complete loss of data) compel me to stick with the regular, non-PAE configuration on i386 systems. But, someone else may have had better luck and set your mind at ease. Regards, Mike
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