Subj : Re: Running XP on a 64bit processor computer To : All From : nospam@needed.invalid Date : Thu Jan 31 2019 19:16:25 Path: eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.o rg!.POSTED!not-for-mail From: Paul Newsgroups: microsoft.public.windowsxp.general Subject: Re: Running XP on a 64bit processor computer Date: Mon, 20 Nov 2017 22:00:39 -0500 Organization: A noiseless patient Spider Lines: 106 Message-ID: References: <1lj61d983lb39hp90gfmn4des62egh240s@4ax.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Tue, 21 Nov 2017 03:00:39 -0000 (UTC) Injection-Info: reader02.eternal-september.org; posting-host="3947a3c85345ac072b97118d29bffaec"; logging-data="31288"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+MRbPLBTqhnea88qgZTbmd5UbJ3FpLHUs=" User-Agent: Ratcatcher/2.0.0.25 (Windows/20130802) In-Reply-To: <1lj61d983lb39hp90gfmn4des62egh240s@4ax.com> Cancel-Lock: sha1:pGLsEQSJECbu8HK5uLb8p6iM3gM= Xref: feeder.eternal-september.org microsoft.public.windowsxp.general:134650 james@nospam.com wrote: > I have a computer which originally came witt Vista. It's a 64bit > machine. I got it with XP Pro SP3 installed. I know that XP is 32bit. > I'm a little puzzled about this. Can XP (or any 32bit OS) run on a > computer that has a 64bit processor? > > (I know you cant do it the other way. You cant run a 64 bit OS on a 32 > bit machine). > > Does running a 32 bit OS on a 64bit machine work any better or worse > than it does using an actual 32 bit computer? > The CPU has two modes. Mixed mode supports 32-bit and 64-bit instructions at the same time. The processor knows which are which, via the OPcode decoder. It knows how much of each to "suck in", based on that. 32-bit and 64-bit OSes both work in mixed mode. So yes, WinXP x32 runs on a 64-bit CPU, as long as the CPU is in mixed mode. And it is. ******* I have one table somewhere, which claims these CPUs also have a "pure" 64-bit mode. Why anyone or any hardware company would think of invoking that, is anyones guess. As the Mixed Mode is so much nicer. There is at least one Linux distro, that runs in pure 64-bit mode. Maybe they did it as a bar bet or something. ******* On Core2 processors, the x32 instructions execute faster than the x64 instructions. This is due to a packing mechanism the CPU uses. It has some 64 bit plumbing, which can suck in two 32 bit things at a time. That packing mode adds maybe 5% more performance (for certain programs) to the CPU. When you switch to the 64-bit OS, you have to balance any (slight) efficiency gain from 64-bit wide data handling, versus the loss caused by the lack of packing. More modern processors no longer have that distinction, and then 64-bit wins as long as the data you need to handle is really wide. For counting loops, many counting loops use small numbers. The 32-bit storage handles them just fine. Using a 64-bit OS, doesn't make such counting work any better. However, if you do arbitrary precision arithmetic with GMP library, the 64-bit processing makes a big difference. Code run in 64-bit mode is 70% more efficient than code run in 32-bit mode. I ran some C code for Mersenne Primes on top of GMP and benchmarked it. That's the most speedup I know of, because of using a 64-bit OS. For many other things, the 64-bit OS buys you... sweet nothing. The main benefit of 64-bit, is allowing a program to use more than 2GB of memory. Like the Firefox people who want to eat all the RAM in the computer. That's why they're pushing the 64-bit version. I sometimes use 32-bit versions of programs, for the express purpose of "containing" them. It's a kind of memory quota, and prevents runaway behavior. ******* The only thing that doesn't work, is installing a 64-bit OS on a 32-bit-only CPU. And you know that already. The installer disc would tell you early on, it cannot be done. For example, my AthlonXP CPU is 32-bit only, which means half the DVDs in the house cannot be used on it (for OS installs). A couple of my early Pentium 4 processors are in that predicament (32-bit only). ******* The single biggest issue with putting WinXP on a new machine ? The AHCI driver for the HDD interface. If you get a blue screen and an "Inaccessible Boot Volume" error, that's what is blocking it. You need to press F6 early in the install and offer a floppy diskette with the AHCI driver. WinXP has *some* in-box drivers, so if you configure the BIOS correctly, there won't be an issue. If you leave it in AHCI... there will be an issue. If you have the small Intel TXTSETUP.OEM file set, you can fix it via F6. The prompt appears at the bottom of the screen, early in the WinXP install process. I think my laptop is stuck in AHCI mode, so that's the first issue I'd have to deal with. You can also slipstream an AHCI driver into a WinXP installer disc, and then when installing, you don't need to press F6 and you don't need a floppy drive. So that's how heroic WinXP users running newer hardware can do it. Paul --- Platinum Xpress/Win/WINServer v3.1 * Origin: Prison Board BBS Mesquite Tx //telnet.RDFIG.NET www. (1:124/5013) .