What's better: dual-channel memory mode or a bit more RAM?

[Adam Funk]

On 2011-04-27, compdoc wrote:

>> Will A or B give me better performance?
>
>
> One thing to try is memtest86+. Test both A and B configurations, and memtest 
> will tell you how fast the bandwidth to the ram is. You probably won't see a 
> lot of difference.
>
> I've been reading that with quad cores, you want to run in unganged mode. 
> (which turns off dual-channel mode) This allows the cpus to access the banks 
> of ram independently. This is supposed to be faster.

The CPU is just an Athlon 64 3800+.  I ran memtest86+ and I a choice
between the following.

   Memory:  2047M  2126 MB/s
   [dual-channel]

   Memory:  2559M  1103 MB/s
   [single-channel]

So the dual-channel does affect the bandwith (if I'm interpreting the
output correctly and the numbers quoted above are what you mean by
"bandwidth").  The first pass took twice as long in the second
configuration --- I guess this corroborates my interpretation?


BTW, are the CAS numbers significant?

   Settings: RAM: 159 MHz (DDR319) / CAS : 2.5-3-3-7 / DDR1 (128 bits)
   [dual-channel]

   Settings: RAM: 159 MHz (DDR319) / CAS : 2.5-4-4-7 / DDR1 (128 bits)
   [single-channel]


(Thanks to everyone for all the advice.)