Max Ram?

milverton · June 2, 2011, 12:04am

[size=][FONT=“Arial”]Maybe I should read all of the posts as the answer to my question may well be in one of them. I apologise for being lazy:embarrassed:

Question: What is the maximum extended memory that is supported by OpenSuSE 11.4 64 bit?

Thanks in anticipation.[/size][/FONT]

jdmcdaniel3 · June 2, 2011, 12:09am

In summary, the 64-bit architecture has the following advantages:

A 64-bit application can directly access 4 exabytes of virtual memory, and the Intel Itanium processor provides a contiguous linear address space.

64-bit Linux allows for file sizes up to 4 exabytes (2 to the power of 63), a very significant advantage to servers accessing large databases.

Please consult your desktop, laptop, motherboard manufacturer or your wallet for exact details before attempting to insert 4 exabytes of memory into your computer. lol!

Thank You,

martin_helm · June 2, 2011, 12:14am

The architectural limit imposed by the CPU is 48 bits for adressing which is
256 TB. This is as far as I remember not usable due to several constraints
which limit it to as far as I remember 16 TB. But I am also now to lazy to
look up the proper links which give an authoritative answer.
But with current RAM technologies you will have a hard time to come near to
that limit with a standar desktop or server system.

martin_helm · June 2, 2011, 12:52am

martin_helm wrote:

> The architectural limit imposed by the CPU is 48 bits for adressing which
> is 256 TB. This is as far as I remember not usable due to several
> constraints which limit it to as far as I remember 16 TB. But I am also
> now to lazy to look up the proper links which give an authoritative
> answer. But with current RAM technologies you will have a hard time to
> come near to that limit with a standar desktop or server system.
>
The precise answer is in the kernel sources
/usr/src/linux-2.6.34.8-0.2/arch/x86/include/asm/sparsemem.h


* MAX_PHYSADDR_BITS            2^n: max size of physical address space

which is currently set to


# define MAX_PHYSADDR_BITS      44

for x86_64 architecture.
2^44 = 16 TB

markone · June 2, 2011, 1:15pm

Well, while they say that there are no stupid questions, there are certainly some questions, which, if answered directly, do nothing to help the OP.

Looking at the website of my local dealer, the largest memory modules that they stock are 4G, and these cost £26 each. For most consumer boards, with a single memory space, you’ll have a maximum of 4 slots. So, even doubling those sizes, the maximum memory that you could plug in would be 16 G. And, even at a future time at which 16G modules become available, 64G would be the maximum practicable in a board with four slots.

@martin_helm

The architectural limit imposed by the CPU is 48 bits for adressing which is
256 TB. This is as far as I remember not usable due to several constraints
which limit it to as far as I remember 16 TB. But I am also now to lazy to
look up the proper links which give an authoritative answer.

The limit imposed by the hardware can be one of several numbers, depending on which exact hardware we are talking about. If we dismiss older hardware (there are relatively recent chipsets with a 768M limit, which is a bit shocking) then we could be talking about processor limits of 36 bits (probably the P4 is the only example of this still in common use), 40 bits or 48 bits, although, in practice, chipset limits may well be lower.

If 32 bits worth of memory address space costs you £26 to fill, then 36 costs £406, 40 bits £6496 (512 sockets on your motherboard?). This is money, and it is left as an exercise for the interested reader to work out how deeply in debt you would be at 48 bits of address space, even if you could use it. I’m too indolent to be even interested. Or get my pocket calculator out; I take no responsibility if I’ve made an error in calculating those figures, but, rest assured, they get big fast.

The memory limits for other Archs, such as Itanium, Power, ARM, MIPS and PA-Risc variants will, of course, be different from those of x86.

DenverD · June 2, 2011, 1:33pm

On 06/02/2011 12:06 AM, milverton wrote:
>
> QUESTION: WHAT IS THE MAXIMUM EXTENDED MEMORY THAT IS SUPPORTED BY
> OPENSUSE 11.4 64 BIT?

a LOT more than either a lazy person or a small company can afford to buy…

and, you didn’t say about your motherboard, but i guess Linux can
service several hundred times more than your board can hold…

–
dd CAVEAT: http://is.gd/bpoMD
[NNTP via openSUSE 11.4 [2.6.37.6-0.5] + KDE 4.6.0 + Thunderbird 3.1.10]
Dual booting with Sluggish Loser7 on Acer Aspire One D255

milverton · June 2, 2011, 3:21pm

Firstly, I am grateful for the kind replies, all of which are appreciated:)

I am in the fortunate position of being able to afford to invest whatever I need (well, to the point below divorce of course) to improve my small but, busy infrastructure. The particular machines that are running OpenSuSE 11.4 (in server mode) are both DL585 G6 boxes. I also have two DL385 G1 boxes that I intend to use with OpenSuSE 11.4. That may help in clarifying the RAM support where OpenSuSE 11.4 is installed.

Am I correct in thinking, from your collective responses, that I can install up to 64GB total RAM to a machine? OpenSuSE is 64 bit, so I guess it must be able to address at least 64GB (maybe 256GB?) You will know what my servers will support as they are very common boxes. I too know what they will support but, that wasn’t my question.

Thanks again for your interest and replies.

martin_helm · June 2, 2011, 3:09pm

markone wrote:
>
> The limit imposed by the hardware can be one of several numbers,
> depending on which exact hardware we are talking about. If we dismiss
> older hardware (there are -relatively- recent chipsets with a 768M
> limit, which is a bit shocking) then we could be talking about processor
> limits of 36 bits (probably the P4 is the only example of this still in
> common use), 40 bits or 48 bits, although, in practice, chipset limits
> may well be lower.
The question was about openSUSE 11.4 64 bit, there is no other architecture
supported by that than the x86_64 which is AMD64 and this has 48 bit for
addressing, the P4 is 32bit, and the (theoretical) limits for that can of
course also be seen in the kernel source (same file I posted, just look at
the ifdef’s). There is also no openSUSE 11.4 for IA64 which you can
download, so this is also out of interest.

The real limit is anyway almost never the CPU but the mainboard, but this
was not the question.