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 Forum index » Advanced Topics » Puppy Derivatives
The PAE myth - to be or not to be PAE
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live

Joined: 10 Feb 2010
Posts: 161

PostPosted: Sat 04 Oct 2014, 10:46    Post_subject:  The PAE myth - to be or not to be PAE  

Some believes that PAE kernel can run on any x86 machine whether 32 or 64 bits, whether they have 256Mb or 32Gb RAM.
This is false believe.
Only NON pae kernel with proper compilation options can run accross any x86 machine whether 32 or 64bits, but FIRST they are 32 bits and SECOND they can address upto 3Gb RAM (whether you have 4 of 16GB, it's still bounds to 3Gb, now you might believe as 2^32 = 4Gb, you might address 4Gb, this not the case, make your own check if you have a contrary believe)

Over the years as the technology matured, 3Gb RAM became more and more a constraint (before it was the 16bits limit and before 8bits and before 7bits).
So to lift this limit of 3Gb, there was 2 options, 64bits cpu or 32 bits pae ENABLED cpu.
The pae ENABLING is a trick to address more RAM (a bit like IPv4 tricks vs IPv6), aka if your 32bits CPU is NOT pae enabled, a pae enabled kernel will not boot.

So what CPU will run pae kernel?
* any 64bits.
But than you surely better with 64bits kernel, as you also have lots of improvements (compilers are than allowed to use more registers, may use SSE2 instructions sets or later, etc.)

* 32 bits CPU who made the junction between the "old" non pae cpu's (for instance "old" Celeron) and 64bits(Pentium IV).
At that epoque, "high end" cpu's such as the Pentium Pro(1995-1998) were already pae enabled, but on the contrary "cheap end" cpu such as Celeron M @1,4Ghz (2005) for laptop were NON pae.
As a personal believe, I think that the number of 32bits enabled pae cpu is way inferior to the number of non enabled pae cpu, by the shear fact that at the beginning apps needed to be ported to 64bits and mostly server and graphic designer were in need for more ram and pay for it.

Conclusion:
if you want a kernel to run any x86 CPU, you use a NON pae kernel with proper 32bits build options.

Voila,

I hope it clarifies some false myth about PAE kernel and compatibility.


Some refs:
* http://en.wikipedia.org/wiki/Physical_Address_Extension
* https://gcc.gnu.org/onlinedocs/gcc-4.8.3/gcc.pdf
* http://en.wikipedia.org/wiki/Pentium_Pro
* http://en.wikipedia.org/wiki/Celeron
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gcmartin

Joined: 14 Oct 2005
Posts: 4355
Location: Earth

PostPosted: Sat 04 Oct 2014, 11:20    Post_subject:  

This has some obvious errors in the opening post on this. The biggest problem is how so many confuse PAE. IT IS NOT SOFTWARE!!! AGAIN, IT IS NOT SOFTWARE!!! PAE is a hardware feature. Some in this community continue to misinterpret manipulating information about benefit to some personal goals. Kinda like Android vs Apple or Beta vs VHS or ....

PAE is hardware and the distro uses it to access memory to carry out the work on behalf of system use, same as distro uses the pre1995 model of RAM access. There are actually 3 access models used in today PCs, pre1995 32bit, PAE 32bit, 64bit. The OS kernels is design specific to these so that work within the system is carried out.

This thread is sharing a preference of whether the author want developers to position themselves around presenting kernels to this community.

The kernel has been designed to take advantage of the operations of the PAE hardware.

Further, when Puppyites worked in testing, there were no elements of stability that would preclude anyone to not use Linux which can support PAE hardware. (over 99% of CPUs manufactured since 1995).

This thread intends to push a PREFERENCE and intends to push developers! We should steer away from this mode of pushing our developers leaving it to them to produces works for our use without entering a positional personal preference that one wants to be generally applied.

ALL USERS should choose a distro based upon its ability to operate on your platform (and if you have multiples on your multiple platforms). If you dont have 64bit dont choose a 64bit distro and dont criticize developers who make 64bit distros. Same is true for 32bit. And be aware, that PUPPY testors several years ago found no loss of either functionality or performance, negating those arguments over some perceptions which existed prior to Puppyite testings.

NO USER NEED BE CONCERNED as the distro produced by developers of this community work, perform admirably, and are stable no matter the RAM size.

DO NOT BE AFRAID as the thread indirectly suggests. No one is going to lose data or service because your distro takes advantage of your CPU's ability. Those distros are built to exercise hardware to your benefit.

Whether one agrees or not, emotionally, it works well for anyone on us with no side effects that stand out.

Here to help

BTW: Architecture and behavior goes hand in hand. If you have a PAE distro you run, use the "free" terminal command to get a firsthand appreciation of what Linux does for you. Its extremely simplistic, but accurate. Let PUPPY behavior and its reports be your evidence.

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p310don

Joined: 19 May 2009
Posts: 717
Location: Brisbane, Australia

PostPosted: Sat 04 Oct 2014, 21:36    Post_subject:  

Simple tips:

32bit CPU
Less than 3 gig RAM - PAE offers no advantage (but often no disadvantage, it either does or doesn't work)
More than 3gig RAM - PAE offers an advantage

64bit CPU
32bit PAE & non PAE OS will work perfectly fine
64bit OS offers many advantages.
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-MoMo-

Joined: 04 Oct 2014
Posts: 10

PostPosted: Sat 04 Oct 2014, 22:10    Post_subject:  

Can someone explain what I ask in my original post ....
http://www.murga-linux.com/puppy/viewtopic.php?t=95944

Basically, does a 64-bit Linux use true Dual-Channel RAM control the same
as a Windows 64-bit OS (win 7 or win 8.1 64-bit)
Or does Windows look for some special BIOS routine code
for Dual-Channel mode?

Because the Linux 64 (FatDog64) works with 4GB
(two 2Gb in each of 2 sockets)
But the Win 64-bit OS goes to re-boot on the same system w/ 4GB

That same system works with 3GB used on Win 64-bit OS
(2GB in 1 socket + 1GB in 2nd socket)

Please see the other post, linked above, for the full explanation of my subject.

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live

Joined: 10 Feb 2010
Posts: 161

PostPosted: Sun 05 Oct 2014, 05:20    Post_subject:  

Quote:
This has some obvious errors in the opening post on this. The biggest problem is how so many confuse PAE. IT IS NOT SOFTWARE!!! AGAIN, IT IS NOT SOFTWARE!!! PAE is a hardware feature. Some in this community continue to misinterpret manipulating information about benefit to some personal goals.

Exactly, PAE is hardware as put in the references links, but like floating point arithmetic the compiler options might take advanges or not of this hardware - for instance if you force the compiler not to use floating point arithm, then it will emulate floating point arith.

Quote:
32bit CPU
Less than 3 gig RAM - PAE offers no advantage (but often no disadvantage, it either does or doesn't work)

Precisely, regarding 32bits cpu's PAE will only work on 32bits pae. Some people "complain" about it and therefore do need plain simple non pae kernel. The ability to go retro with32bits cpu is expressed by some linux distro which have target compilation as i386, i486, i586 or i686(Arch for instance).
Therefore pae kernel ought to be compiled with a minimun i686 target, as if one would try to run a i386 pae build on a pentium(i586) it would never boot has it has no pae, eventhough the build is i386!

Quote:
Further, when Puppyites worked in testing, there were no elements of stability that would preclude anyone to not use Linux which can support PAE hardware. (over 99% of CPUs manufactured since 1995).

Yes, non pae hardware will never run a pae puppy....
99% of cpu since 1995, I don't know where this affirmation and consider is a safe bet for San Diago, but more challenging in poor area in the world, were old hardware lands. But I would share your viewpoint that world wide the majority of cpu have pae, because most are 64bits, in which case you better of with a 64bits OS.

Quote:
if you want a kernel to run any x86 CPU, you use a NON pae kernel with proper 32bits build options.

True, but I meant: if you need to run any x86 CPU, you use a NON pae kernel with proper 32bits build options, otherwise if you have a 64bits cpu use a 64bits os.

Quote:
If you dont have 64bit dont choose a 64bit distro and dont criticize developers who make 64bit distros.

Sad, but as for the rest, either gcmartin has been recently agressed or has a tendancy to mythomania
Quote:
* any 64bits.
But than you surely better with 64bits kernel
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