[P965 NEO] Why max memory 8gb but don't support 2gb module?

Question

Why max memory supported is  8gb and has 4 slots,  but don't support 2gb DDR2 800mhz module?
The memory is CORSAIR PC2-6400 XMS2 DHX DUAL CHANNEL 2GB.
Sorry with my English.
Main Board
RAM

Answer 1

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Why max memory supported is  8gb and has 4 slots,  but don't support 2gb DDR2 800mhz module?
This is an (Intel!) chipset (memory controller) limitation rather than a board or BIOS problem.  Intel states it somewhat differently:
http://www.intel.com/Assets/PDF/datasheet/313053.pdf
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Supports 256-Mb, 512-Mb, and 1-Gb technologies for x8 and x16 devices (DDR2
800MHz 1Gb technology not supported)
Intel refers to the density rather than the memory capacity/size.  Look at this Kingston module model for example:
http://www.valueram.com/datasheets/KVR800D2N5_2G.pdf
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The components on this module include
sixteen 128M x 8-bit DDR2-800 SDRAM in FBGA packages
"128M x 8-bit" refers to the density of the memory chips used on those modules (=1024 Mbit or 1Gbit (1Gb)).  There are sixteen of those 128M x 8-bit chips on the module which gives you a capacity of precisely 1024Mbit x 16 = 16384 Mbit (2024 MByte). 
A 2GB DDR2-800 module that meets the Intel specifications for the P965 memory controller (512Mbit maximum density for DDR2 800) would need to have 64M x 8-bit components but would need precisely 32 of those chips to reach a capacity of 2GByte.  Try to find a DDR2-800 module that can hold 32 memory chips and you will be able to run them @DDR2-800.  To my knowledge such modules do not exits (the module I used as an example has 8 chips on each side).
That is where the limitation comes from (it is not an MSI thing).