Ram for dual channel

[cyrux]

I am about to pruchase a 256 Mb ddr for a 845 board i have. I already have a 256 Mb ram (ddr) running a 333 Mhz. I want to add another 256Mb in another slot. Even if i buy of 400Mhz it will be underclocked to 333 Mhz so thats not a pob. What i wanted to know is whether i have to take of the ram timings also ??? IS it necessary that the ram timings also match.
i m not OCing the ram

[mohit]

Rules to Enable Dual Channel Mode

To achieve Dual Channel mode, the following conditions must be met:

Matched DIMM configuration in each channel

Same Density (128MB, 256MB, 512MB, etc.)

Matched in both Channel A and Channel B memory channels

Populate symmetrical memory slots (Slot 0 or Slot 1)

Note: Configurations that do not match the above conditions will revert to Single Channel mode.

The following conditions do not need to be met:

Same brand

Same timing specifications

Same DDR speed

Note: Memory channel speed is determined by the slowest DIMM module populated in the system.

Source :
http://www.intel.com/support/motherboards/desktop/sb/CS-011965.htm

[mohit]

btw 845 board does not support dual channel...

[samrulez]

U R Mobo does not support Dual Channel mODE