Date: Wed, 2 Jul 2003 02:06:42 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: Joshua Oreman <oremanj@webserver.get-linux.org> Cc: questions@freebsd.org Subject: Re: 4GB RAM limit? Message-ID: <20030702000642.GA5018@falcon.midgard.homeip.net> In-Reply-To: <20030701234655.GA72522@webserver.get-linux.org> References: <BB2783B4.34F62%list@zettai.net> <20030701234655.GA72522@webserver.get-linux.org>
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On Tue, Jul 01, 2003 at 04:46:55PM -0700, Joshua Oreman wrote: > On Tue, Jul 01, 2003 at 06:30:13PM +0000 or thereabouts, george donnelly wrote: > > hi > > > > I've got a 4.7 freebsd machine and after upgrading from 4 to 6GB of RAM, top > > does not recogmize the other 2 GB (only shows 4) and actually there was a > > message that said "ignoring 2 GB". > > > > Can anyone shed light on this or suggest where i can look to understand > > this? > > AFAIK, on i386 the maximum addressable memory space is 4096 MB. > Here's why: > C pointer = 4 bytes = maximum value 4294967296 Yes and no. i386 addresses are indeed 32 bits which means that a process can only address 4GB worth of memory. On the Pentium Pro and later x86 CPUs there some special tricks that can be used to have a physical address space of 36 bits (64 GB memory), even though a single process still only can use 4 GB. FreeBSD 4.x and earlier does not have any support for those tricks so it cannot use more than 4 GB of RAM. FreeBSD 5.1 and later does have support for PAE (Physical Address Extension) so it can handle up to 64 GB RAM (while a single process is still constrained to a 32-bit address space.) -- <Insert your favourite quote here.> Erik Trulsson ertr1013@student.uu.se
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