Does RAM Module Size have an effect on overall data rate

A similar question has been asked here: One large ram module or two smaller ones?

But my question relates to a very specific scenario.

We recently attempted to upgrade a server from 8 4GB RAM modules to 8 8GB modules

After doing this, we noticed a major performance reduction when running a specific task. We have a process that reads a large volume of data into memory for use in complex calculations. With the old RAM modules, this process took about 15 minutes. With the larger RAM modules, this process now takes about 40 minutes. Nothing else has changed.

The RAM module specs aren't identical, but this is such a large drop in performance, it makes me think something else is going on here.

Could putting 8GB on a single module cause a lower overall data rate on what I assume are effectively sequential writes to the RAM (populating the data cache in this case).

Or perhaps someone can point to some other difference in the memory modules that could account for this?

Matthew Brophy

Posted 2014-02-11T14:56:18.240

Reputation: 21

@Ramhound Is the new memory significantly slower? What is it that makes it slower? The new memory has higher clock speed and lower cycle time. The new memory does have a higher Cas - but this should be partially offset by the higher clock. – Matthew Brophy – 2014-02-11T15:36:36.097

1@user299239 Even if the specifications say it is higher, you should still check what speed it actually is running at. Some faster memory defaults to a slow speed for compatibility and needs to be manual set higher in the BIOS. – Dan D. – 2014-02-11T15:38:26.933

1The frequency of the modules are different. CL7 vs CL9. As I indicated that would explain a small different but not a 1.5x difference. – Ramhound – 2014-02-11T16:10:57.587

Answers

Your 8 GB modules should normally be FASTER.

That is: If your motherboard and bios supports them properly. If the hardware identifies the timing specs incorrectly and clocks them much lower than anything could happen.

Run a utility like CPU-Z on the server and check if the specifications reported by CPU-Z match the specs of RAM.

Another thing: It could be that the way the software handles the data-set in RAM is somehow inefficient or doesn't scale up with the amount of RAM available. In that case adding more RAM may in effect slow things down, but that is a design flaw in the software.

Tonny

Posted 2014-02-11T14:56:18.240

Reputation: 19 919

Software in this case is just .NET. It is pulling data into Dictionary objects. – Matthew Brophy – 2014-02-11T15:38:25.840

Are you sure all the memory is recognized by your system? What does the system properties page show for your memory amount?
Open up Performance Monitor to investigate how Windows is using your memory. Another program may be 'stealing' memory or Windows may be using more or less memory for disk caches, and things may need to be reconfigured to make the newly installed memory available for your program to use.

Bert

Posted 2014-02-11T14:56:18.240

Reputation: 1 476