Why are memory speeds so different?

MikeyCarter · 08-09-2011, 03:54 PM

I've been gathering stats on all the computers in my reach and found something I can't quite explain.

Here's how I do the memory test:

Code:

sysbench --num-threads=1 --test=memory --memory-access-mode=rnd --memory-oper=read --memory-total-size=1G run

My computers I get (Most of my older ones are < 150 MB/s):

Code:

Dell PowerEdge T100 - 8G Ram - X3360 CPU - 2934.1 MB/s
Dell PowerEdge 840  - 6G Ram - X3220 CPU - 2161.6 MB/s
Inspiron 530s       - 3G Ram - E2200 CPU - 1918.3 MB/s
G41M-ES2L           - 4G Ram - E5400 CPU -  468.1 MB/s
G41M-ES2L           - 3G Ram - D 915 CPU -  359.3 MB/s

Can anyone tell me why the last two are so much slower? My first thought was the first two are servers with Xeon processors... but then that doesn't explain the 530. Then I thought memory speed but when you start swapping memory between the machines you get the same results. (Actually one of the G41M-ES2L has the memory from the PE 840.)

H_TeXMeX_H · 08-09-2011, 04:31 PM

Code:

PC                  - RAM    - CPU       - transfer    - b/c  - FSB
Dell PowerEdge T100 - 8G Ram - X3360 CPU - 2934.1 MB/s -  8.5 - 1333 MHz
Dell PowerEdge 840  - 6G Ram - X3220 CPU - 2161.6 MB/s -  9.0 - 1066 MHz
Inspiron 530s       - 3G Ram - E2200 CPU - 1918.3 MB/s - 11.0 - 800 MHz
G41M-ES2L           - 4G Ram - E5400 CPU -  468.1 MB/s - 13.5 - 800 MHz
G41M-ES2L           - 3G Ram - D 915 CPU -  359.3 MB/s - 14.0 - 800 MHz

The two most important numbers being bus/core ratio:
http://en.wikipedia.org/wiki/Bus/core_ratio
and FSB speed:
http://en.wikipedia.org/wiki/Front_side_bus

Also try the stream benchmark:
http://www.cs.virginia.edu/stream/

PTrenholme · 08-09-2011, 04:36 PM

Redacted - H_TeXMeX_H said it better and sooner.