Re: [phenixbb] fem command/memory error

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Yes, a 64 bit machine can address an incredible amount of memory... If all 64 addressing lines are brought out of the CPU chip. The chips (and motherboards) I'm aware of never do. It is just not cost effective since most people can't afford exabytes of RAM. Most desktop systems are limited to 16GB but you can get some motherboards with 32GB capability. I built a desktop system with 32GB last summer for about $2000. Servers are designed to hold more memory, at a much greater cost. It was the same story for 32 bit computers. The VAX 11/780 I worded on as a PhD student was 32 bit but could only address 4MB of RAM. The lab could only afford to buy that much late in my PhD work. Dale Tronrud On 5/14/2014 9:14 AM, Tim Gruene wrote:

Hi Roger,

not quite 16GB:

32 bit gives 2^ 32 / 1024^3 GB = 4 GB 64 bit: 2^64 / 1024^3 = 17179869184 GB = 16 Exa B

Cheers, Tim

On 05/14/2014 05:13 PM, Roger Rowlett wrote:

...

4 Gb is the limit of addressable memory for 32-bit machines. The amount of usable memory (RAM) is anywhere from around 2-3 Gbyte depending on hardware configuration. Some hardware (e.g., a graphics card) reserves memory space for itself, decreasing the amount available for usable RAM.

I believe all relatively modern (last 5-10 years?) CPUs are 64-bit capable. A 64-bit machine should be able to address 16 Gbyte of memory. (Minus hardware deductions for usuable memory space.)

Cheers,

_______________________________________ Roger S. Rowlett Gordon & Dorothy Kline Professor Department of Chemistry Colgate University 13 Oak Drive Hamilton, NY 13346

tel: (315)-228-7245 ofc: (315)-228-7395 fax: (315)-228-7935 email: [email protected]

On 5/14/2014 11:05 AM, Nathaniel Echols wrote:

...

On Wed, May 14, 2014 at 1:44 AM, Matteo Colombo mailto:[email protected]> wrote:

My OS is Ubuntu precise 12.04 LTS, system 32 bit

One note of caution: if you are running a 32-bit architecture or OS, upgrading the memory may not help, because it will be limited in how much it can address at once. (I forget if the limit is 2GB or 4GB; it may be OS-dependent.) At this point I would recommend using 64-bit for everything if possible, and especially not purchasing any systems that are 32-bit only. (Are these even sold any more?)

-Nat

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