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 Forum index » Advanced Topics » Hardware
Of interest to Users and Distro Developers about PCs
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Joined: 14 Oct 2005
Posts: 6730
Location: Earth

PostPosted: Mon 26 Mar 2012, 17:45    Post subject:  Of interest to Users and Distro Developers about PCs
Subject description: Regarding PAE and RAM

PAE is a feature of 32bit CPU operations to access all RAM including that above 3GB all the way to 64GB. It has been around for over 15 years. It is NOT a replacement for 64bit, nor does it make a 32bit OS behave like a 64bit OS. Its mere operation is to allow the OS to be able to address ALL RAM on the system.

There are occasions when a particular family of processors may or may not be able to boot a PAE distro. or provide near-native operations to guests Virtual machines. Most PC uses will never experience any difficulty in using any 32bit OS (PAE/non-PAE). BUT, on very rare occasions, some users will experience a problem with the PAE distros

Over 6 years ago the CPU vendors added a feature to allow guests running in a Host VM to have near native performance. This feature is known as KVM. You will find that this feature in built-in to most 64bit CPUs. Again, on occasions, some users will have purchased PCs where the CPU may be missing this feature, as well.

Note: PAE is also discussed
Can 32-bit Puppy use >3 GB of RAM? (Yes, with PAE)
New Puppy Linux with PAE uses all RAM on your PC(s)
64bit PCs and PAE in Puppy World - Facts versus Myths

Here's a partial response I got from AMD. Most SEMPROs since 2007 and alll Athlons and pure 64bit AMDs should boot a 32bit PAE distro without issues. This is not to say that a vendor may/may-not have included a prior SEMPRO in their manufacturing run. All other 64bit AMD and Athlons will operate well with PAE and non-PAE distros.


Further, there are occasions that a modern (less than 5 years old) 64 bit Intel "may" BE MISSING support for the VM hardware support which gives near native OS operations. This is commonly referred to as KVM or hypervisor microcode in the CPUs.


For Intel CPUs; some Intel Celerons before 2007 may not have a feature which allows PAE to operate as it does on most of the Intels in circulation since Intel introduced PAE in PentiumPros


In testing done by this Puppy community a year ago, it was found that 512MB+ PAE AND not-PAE Puppy distros perform equally with PAEs having merely a "perceived" advantage over non-PAEs. The primary measurable advantage PAE offers is its ability to use ALL of the RAM on your PC. In essence, you can start with 512MB and keep adding as much RAM as you choose without ever having to change the OS to use all of it.


Advice for all who have PCs built since 2007
  • in over 95% of the cases, PAE should work and expose all RAM it sees for OS usage in the Puppy filesystem as extremely high speed I/O. Expect this behavior on most of the processors built sine 2007 without issue. But, check your BIOS too, for an enabling feature. 64bit Puppy OS have NO problem as this is native to them. Also, be aware that some of us have 32bit processors with mote than 4GB RAM that pre-date the 2007 processors which also work just fine with PAE Puppy distros.
  • For VM hardware assist, there is a Linux command that can be used to show whether your processor has the capacity to allow near-native virtual operations of your guest OSes. Check your bios as well here as some server models deliver with an enabling BIOS feature
  • And, I am told by my hardware guru, that if a processor has the VM hardware assist feature, it is ALSO enabled for PAE operations (unless there is a bios selection that turns it off).
Hope this helps all distro developers and users alike as more and more memory modules get bigger and cheaper by the day.

Anyone who has information relating to KVM or PAE that the community should be aware from an individual experience , please share that here for all to see..
 Description   AMD directed me to this source for SEMPRO. http://en.wikipedia.org/wiki/Sempron
 Filesize   96.36 KB
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