Re: Debian Lenny 32
On 12/30/2011 8:59 AM, Camaleón wrote:
> On Thu, 29 Dec 2011 21:32:06 -0600, Stan Hoeppner wrote:
>
>> On 12/29/2011 10:53 AM, Camaleón wrote:
>>> On Thu, 29 Dec 2011 18:26:28 +0200, Mohamed Daif wrote:
>>>
>>>> What is the maximum RAM supported in Debian Lenny 32bit .
>>>
>>> It should be 64 GiB with a PAE enabled kernel (bigmem).
>>
>> 64GB max for the kernel, but userspace processes are still limited to a
>> 4GB virtual address space. Thus if one has an application, say a
>> database or medical imaging app (think MRI), that requires direct access
>> to say, 32GB of RAM, one should be using an x86-64 kernel and an
>> application compiled for an x86-64 target.
>
> That's a self-imposed limitation.
>
> It could be by-passed by using "memory mapping" techniques (this is
> documented in the wikipedia page you pointed out about PAE, which
> specifically mentions "mmap()") but not many linux applications are
> making use of it, I'm afraid, contrary what happens on Windows systems.
> In the end, applications that need to handle/move big quantities of data
> directly from the RAM will benefit of a pure 64-bits OS.
Mostly correct. Using mmap() to get access to all that extra memory
still has significant limitations.
Note that 64 bit Linux has been around long enough that there was no
motivation for anyone to write a convoluted large memory application for
32 bit x86 PAE systems. 64 bit Linux has been running on Alpha and
SPARC since the late '90s, both platforms offering up to 8GB on
workstation hardware and 128GB on servers, with native 64 bit flat
addressing. 64 bit Itanium systems hit the market in the early 2000s
with most workstations offering 16GB of RAM and servers offering up to 1TB.
Thus, anyone serious about writing an app that needed more than a direct
4GB address space was doing it on non-x86 hardware, of which there was
plenty. x86-64 arrived around the same time as IA-64, putting the nail
in the "large memory" x86 coffin, from an application developer standpoint.
Worth noting is that to date, AFAIK, the only mainstream Windows
applications ever written that take good advantage of PAE are MSSQL
server and Win32 Oracle. I'd love to hear of other examples, if there
are any.
--
Stan
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