Is CentOS 4.x i386 or i686?

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Abscissa
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Is CentOS 4.x i386 or i686?

Post by Abscissa » 2011/05/09 22:44:41

For CentOS 5.x, the ISOs claim to be i386, but I've heard that they're *really* i686. Is this true of CentOS 4.x as well? Ie, is CentOS 4.x *really* i686, or are the CentOS 4.x distros i386 like they're labeled?

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AlanBartlett
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Re: Is CentOS 4.x i386 or i686?

Post by AlanBartlett » 2011/05/09 23:14:05

The designators [i]i386[/i] and [i]i686[/i] just indicate [b]32-bit[/b].

Do you have a particular hardware / installation query?

Abscissa
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Re: Is CentOS 4.x i386 or i686?

Post by Abscissa » 2011/05/10 00:05:52

Maybe Red Hat/CentOS changes things around (I'm fairly new to Red Hat/CentOS), but normally "x86" (or in some cases "x86-32") is used to indicate 32-bit without specifying anything more specific than that. Usually, i386/i586/i686/etc (while still naturally implying 32-bit) indicate what target things were compiled for. "i386" typically means it doesn't use any instructions that aren't valid on an i386. "i686" typically means that it may use instructions that aren't on anything less than that particular class of x86 CPUs and that it's likely optimized for such a system.

After all, while the later x86 CPUs are fully backwards compatible with the earlier ones, the later ones DO also add extra instructions that are invalid on the older ones, and they also tend to have different characteristics for optimization purposes. There are many cases of opcodes and opcode sequences that produce optimal speed on an i386 but are sub-optimal on an i686.

[quote]Do you have a particular hardware / installation query?[/quote]

Yea, and that was it, really. I'm on i686 hardware, and I plan to install this into a VM. But CentOS 4.2 was running really slow in the VM, so I'd like to get as much performance boost as I can. Which, at least in part, means using the default install if it's i686, or using the i586 install if the default one is really just i386. Hence "Is CentOS 4.x i386 or i686?"

foxb
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Is CentOS 4.x i386 or i686?

Post by foxb » 2011/05/10 13:26:17

From my experience I'll say mostly i686, but in contrast with 5.x it does not require i686 and will run on i586 (did not have the HW to test for i386)

But the question here is why it is running slow in VM...

First what VM you are using and what is slow?

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Re: Is CentOS 4.x i386 or i686?

Post by pschaff » 2011/05/10 17:56:58

Welcome to the CentOS fora. Reading [url=https://www.centos.org/modules/newbb/viewforum.php?forum=47]FAQ & Readme First[/url] is recommended for new users.

[quote]
Abscissa wrote:
...
Yea, and that was it, really. I'm on i686 hardware, and I plan to install this into a VM. But CentOS 4.2 was running really slow in the VM, so I'd like to get as much performance boost as I can. Which, at least in part, means using the default install if it's i686, or using the i586 install if the default one is really just i386. Hence "Is CentOS 4.x i386 or i686?"[/quote]
For any of the ix86 32-bit RHEL-derived distros i386 is a bit of a misnomer. An i686 capable processor is required, except where i586 is provided, and that is not well supported. The i586 version is only meant for processors that support [b][i]only[/i][/b] the i586 instruction set and are not i686-compatible.

All packages are i386 except for noarch and a few that have specific optimizations.[code]
# cd /share/CentOS/4.9/os/i386/CentOS/RPMS/
# find . ! -name \*.i386.rpm | grep -v noarch | sort
./glibc-2.3.4-2.43.i686.rpm
./kernel-2.6.9-89.EL.i586.rpm
./kernel-2.6.9-89.EL.i686.rpm
./kernel-devel-2.6.9-89.EL.i586.rpm
./kernel-devel-2.6.9-89.EL.i686.rpm
./kernel-hugemem-2.6.9-89.EL.i686.rpm
./kernel-hugemem-devel-2.6.9-89.EL.i686.rpm
./kernel-smp-2.6.9-89.EL.i586.rpm
./kernel-smp-2.6.9-89.EL.i686.rpm
./kernel-smp-devel-2.6.9-89.EL.i586.rpm
./kernel-smp-devel-2.6.9-89.EL.i686.rpm
./kernel-xenU-2.6.9-89.EL.i686.rpm
./kernel-xenU-devel-2.6.9-89.EL.i686.rpm
./nptl-devel-2.3.4-2.43.i686.rpm
./openssl-0.9.7a-43.17.el4_7.2.i586.rpm
./openssl-0.9.7a-43.17.el4_7.2.i686.rpm
./openssl-devel-0.9.7a-43.17.el4_7.2.i586.rpm
./openssl-perl-0.9.7a-43.17.el4_7.2.i586.rpm[/code]
Note that CentOS 4.2 is [b]seriously[/b] obsolete and hence unsupported.

You may want to start a new Topic with an appropriate subject if your real concern is optimizing the performance in a VM.

Abscissa
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Re: Is CentOS 4.x i386 or i686?

Post by Abscissa » 2011/05/10 19:12:30

Thanks, all :-) I understand now.

[quote]
pschaff wrote:
Note that CentOS 4.2 is [b]seriously[/b] obsolete and hence unsupported.
[/quote]

Yea. There's "sort of" a reason for that, but I realize now it's an invalid reason: My original, original problem was that I needed to be able to compile CGI apps to run on a CentOS-based shared webhost. But compiling it on my (K)Ubuntu 10.04 machine resulted in binaries the server was unable to handle:

http://ubuntuforums.org/showthread.php?t=1740277

Someone (outside that forum) suggested at least part of the problem may be that compiling on my (K)Ubuntu 10.04 causes it to attempt to link to a newer libc than the server has. So I tried grabbing a deliberately old version of CentOS (v4.2, pretty much at random), installed in a VM, compiled the CGIs inside there, and the resulting binaries *do* now work for me.

Of course, *now* I realize that all the 4.x releases are supposed to have compatible libc's, so I'm switching to 4.9 and figured "Hey, what the heck, may as well do a fresh install."

Sorry if that's getting a little too OT again. I guess I have a tendency to do that...

In any case, I have 4.9 installed now, and I plan to see if I can switch the desktop environment to XFCE (Might end up needing help with that, we'll see). And I also might try just ssh'ing into the VM and using it that way. But if XFCE still seems slow, then yea, I'll start a new thread about that.

And thanks again.

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