Date: Fri, 2 Jul 2004 11:44:17 -0400 From: Kenneth Culver <culverk@sweetdreamsracing.biz> To: questions@freebsd.org, current@freebsd.org Subject: Re: AMD64 vs i386 for FreeBSD Message-ID: <20040702114417.yi3484ck0k0kcco8@www.sweetdreamsracing.biz> In-Reply-To: <20040702152352.GB78489@dragon.nuxi.com> References: <36u63c$231i65@mxip07a.cluster1.charter.net> <20040629103106.gpw4kwscsg88k0c8@www.sweetdreamsracing.biz> <20040629181248.S54069@carver.gumbysoft.com> <20040630011735.8mv40og88c4goko8@www.sweetdreamsracing.biz> <20040702152352.GB78489@dragon.nuxi.com>
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Quoting David O'Brien <obrien@freebsd.org>: > On Wed, Jun 30, 2004 at 01:17:35AM -0400, Kenneth Culver wrote: >> Quoting Doug White <dwhite@gumbysoft.com>: >> >Me either. -current actually supports running i386 binaries in amd64 mode. >> >Thats one of the processor's features. :-) >> >> >You can't run amd64 binaries when booted into an i386 OS, of course. >> >> Yeah you can run x86 but you cant' go into regular 32 bit mode that's all. > > ENOPARSE, can you please restate this? I think what I meant is that once the kernel puts the CPU into "amd64" mode, it can't go back into regular x86 mode. It can run x86 binaries but it's not fully back in x86 mode, and I think some of the x86 instructions are gone in 64-bit mode, so it has to emulate them somehow. From what I understand 32-bit binaries run slightly slower when the cpu is in 64-bit mode because of this. From what I've read, you can't make a kernel go back into normal x86 mode until you reboot. You probably know about all this better than I do, it's been a long time since I read any tech specs for the cpu. Ken
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