Date: Thu, 21 Feb 2002 16:41:30 +0100 From: "Alex (DDS)" <akruijff@dds.nl> To: =?ISO-8859-1?Q?S=F8ren?= Neigaard <neigaard@e-box.dk> Cc: Erik Trulsson <ertr1013@student.uu.se>, Alex <FreeBSD@cybertron.tmfweb.nl>, questions@freebsd.org Subject: Re: OT: Re: Max RAM supported by Hardware Message-ID: <3C75152A.7040705@dds.nl> References: <1556477954.20020220210026@e-box.dk> <14217053982.20020220215646@cybertron.tmfweb.nl> <15518324328.20020220221756@cybertron.tmfweb.nl> <20020220220028.GA21515@student.uu.se> <193651536.20020221082100@e-box.dk>
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Søren Neigaard wrote: >Wednesday, February 20, 2002, 11:00:28 PM, Erik wrote: > >ET> On Wed, Feb 20, 2002 at 10:17:56PM +0100, Alex wrote: >ET> Sorry, but you just don't seem to understand how things work. >ET> With a 32-bit address space the maximum amount of memory that can be >ET> addressed is 2^32 = 4Gigabytes. This is also the max that FreeBSD >ET> supports on i386. > >Great - So I did understand it right then :) > > >ET> There should be no need to recompile anything. >ET> (Although there has been some reports of problems with >2G but I think >ET> that has been fixed now.) > >That sounds super, I love FreeBSD, it's so much easier than any other >OS I have tried :) > Yes, i made a small error, here. I find that it was a bit to harsh of Erik to say i know nothing about the subject. I mainly tried to explain way it was posible for 64G support given a 32 bits adress bus. I didn't go in to the design choiches of any processor. > > > >ET> Modern x86 CPUs (Pentium Pro and later) can address up to 2^36 (=64G) >ET> bytes of memory. To use the extra memory requires you to play some >ET> tricks with the MMU (Memory Management Unit) to map the memory into the >ET> 4G address space. Even then you cannot really have a single process use >ET> more than 4G. This capability is currently not supported by FreeBSD >ET> and to support it would require some fairly serious rewriting of parts >ET> of the kernel. > This i wrote in other words and holds the key way in some casus a system can handle more memory then 2^n (n = number of bits on the adress bus). Wether or not a pocess can handle more than 4G (in this case) depends on the OS (or at least the design of hardware). > > >ET> On Alpha the max that is supported is 2G. I am not sure why that >ET> limitation exists but it does. > >Strange - It should be able to support much much more. I guess FreeBSD >is mostly for i386, right? Not much being done for other platforms? > The Alpha processor proberbly just doesn't support it. Thus doesn't have the base and offset regestries and memory thats able to handle it. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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