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Old 01-29-2014, 05:27 AM   #16
k3lt01
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Quote:
Originally Posted by gradinaruvasile View Post
So:
So you said this
Quote:
Originally Posted by gradinaruvasile View Post
No it doesnt. 32 bit kernels can be compiled with PAE support that gives you access up to 64GB or something. In fact most recent distro stock i386 kernels have PAE activated.
and plainly that is wrong. 486 doesn't have it activated simply because 486 can't use it.

Quote:
Originally Posted by gradinaruvasile View Post
This is a plain statement that Linux REQUIRES a 64 bit kernel to address more than 4 GB RAM, which is about a fact (NOT opinion) and its NOT true - exactly because the said "686-pae" 32 bit kernels can address up to 64 GB, on 64-bit capable CPUs.
So what? Your statement about older cpus not being able to run i686 was wrong as well but I don't see everyone jumping up and down about that. It was corrected and let be.

Quote:
Originally Posted by gradinaruvasile View Post
So: where is the fact - that other kernels designed for CPUs that arent even capable of this CANT do it - is even relevant here???
To me it is, if your posts are relevant (e.g. i686 can't be run on older cpu) then so are all the others.

Quote:
Originally Posted by gradinaruvasile View Post
Hm. I thought it was started to ask for opinions. My bad.
Indeed it was, some people have a differing opinion to you is that ok? Tobi gave good technical information, you gave personal opinion based on personal experience. Both are valid but for different reasons. ReleaseTheCode gave his opinion and you replied with a "fact" that is not quite accurate.

Quote:
Originally Posted by gradinaruvasile View Post
BTW isnt that forums are for?? For technical details you have Wikipedia, Google etc, but on forums you ask questions to access other real peoples knowledge, opinions and experiences.
Wikipedia can be edited by anyone so cannot really be considered a reliable source. If you don't believe me search out my posts where I even link to the wikipedia page that says so. I know people "ask questions to access other real peoples knowledge, opinions and experiences" problem is what makes yours more valid than anyone else's? I don't have a problem with your opinion I have a problem with you appearing as though your going to have a stroke because your blood pressure has gone through the roof because someone dares to have a different opinion to you. Like I said before "you have yours others have theirs. Live with it."
 
Old 01-29-2014, 05:40 AM   #17
TobiSGD
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About PAE (which by the way on modern systems is not enabled to allow more RAM to be addressed, but because it is needed to make Data Execution Prevention, aka NX, work): https://cl4ssic4l.wordpress.com/2011...lds-about-pae/
 
Old 01-29-2014, 06:12 AM   #18
Ser Olmy
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Isn't it great when a thread devolves into a quarrel that goes on even after it's been marked as [SOLVED]?

To add further to the controversy (perhaps), I'd like to mention that the "bitness" of a CPU isn't actually related to the size of the memory bus. At all. For instance:
  • 8-bit CPUs didn't have an 8-bit memory bus
  • 16-bit CPUs didn't have a 16-bit memory bus
  • Some 32-bit CPUs have a 32-bit memory bus, others don't
  • Most 64-bit CPUs have a 64-bit memory bus, but that's mostly because it's convenient
A so-called 32-bit CPU has internal registers that are 32 bit wide. They can all easily manipulate numbers (data and addresses) in the range 0 to 2^32-1 (which is 4,294,967,295). An 8-bit CPU, however, dealt with numbers from 0 to 2^8-1 (which is 255).

That doesn't mean it's impossible to deal with numbers greater than 4,294,967,295 or 255 on these respective platforms. You just have to divide the larger numbers into smaller chunks, that's all (which makes that YouTube video about the importance of the number "255" in old video games look really silly). Also, some architectures allow(ed) registers to be combined, making is possible to manipulate much larger numbers directly.

Another thing it doesn't mean, is that a CPU would somehow be limited to access a memory space equal to the size of its registers. It certainly isn't. 8-bit CPUs typically had 16-bit memory buses for an address space of 64 kb. The 16-bit Intel 8086 CPU had a 20-bit memory bus (1 Mb), and the 80286 (still a 16-bit CPU) extended this to 24 (16 Mb).

The Intel 80386 was/is a 32-bit CPU which also has a 32-bit memory bus (4 Gb), but three generations later, Intel released the Pentium Pro, still a 32-bit CPU but with a 36-bit memory bus (64 Gb). The extra 4 bits were added using an ugly kludge called "Physical Address Extensions" (PAE), and while the OS can use this to extend its address space to a total of 64 Gb, a process running under said OS can still only access 4 Gb. Some of that is reserved for other purposes, typically leaving processes with a maximum of 3 Gb RAM each.

AMD created a set of 64 bit extensions (known as AMD64 or x86_64) to the Intel 80x86 architecture, and they were licensed back to Intel who decided to call them "EM64T" ("AMD who?" - every Intel executive ever). By way of cross-licensing they eventually also appeared in Intel-compatible VIA CPUs. I don't think you can buy an Intel-based system today that doesn't support "long mode" (64-bit mode). Such processors are also backwards compatible with the old 32-bit modes ("protected mode", "virtual 8086 mode" and "real mode"), meaning you can run operating systems designed for any mode you like.

So, should one choose a 32-bit or 64-bit Linux distribution? Well:
  • If you want to run 64-bit applications, you need a 64-bit OS (the compatibility goes only one way)
  • If you want a single process to be able to access more than 3 Gb memory, you need a 64-bit OS (se the bit about PAE above)
  • If you want to run 32-bit applications, some 64-bit distributions may not work for you (at least not by default), as they may not come with the required 32-bit library files to support 32-bit applications
  • And of course, if your system has more than ~60 Gb RAM, you can certainly forget about using a 32-bit OS
Basically, 64-bit is certainly the future for the 80x86 platform, but there's still a significant amount of 32-bit applications out there, some of which may never be recompiled for x86_64.
 
2 members found this post helpful.
Old 01-29-2014, 09:11 AM   #19
brianL
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Quote:
Originally Posted by Ser Olmy View Post
Isn't it great when a thread devolves into a quarrel that goes on even after it's been marked as [SOLVED]?
Yeah, very entertaining. Trouble is, a Mod usually turns up and spoils the fun.
 
  


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