BigJim said:
But that is listed as an FBDIMM. FBDIMMs are fully buffered, and
both the address and data are handled by the AMB chip on the FBDIMM.
Such DIMMs are typically used on server boards, and would not be
a candidate for your typical desktop motherboard.
I checked a few sites (Crucial, Kingston, and Samsung Semiconductor),
and the largest unbuffered DDR2 DIMMs currently are 2GB capacity.
In terms of types, here are some types:
unbuffered DIMM (UDIMM) - No ECC. Typically used on desktop boards.
Currently looks like DDR2 2GB modules available.
AM2 would use DDR2 modules of this type.
unbuffered DIMM with ECC - Same capacity limits, but with the added protection
of ECC (72 bit wide array, instead of 64 bits). ECC
is supported on some motherboards using X38. ECC is
also supported on AM2 motherboards (by the processor,
as the processor has the memory controller).
registered DIMM with ECC - This is pretty close to raw RAM, except that the
address/control signals pass through register chip(s).
This allows the number of chips on the module to be
doubled. A typical usage situation, might be an
Opteron server board perhaps. You can see the higher
number of chips possible, in a drawing here.
http://www.valueram.com/datasheets/KVR533D2Q8R4K2_4G.pdf
fully buffered FBDIMM - Protocol between DIMM and motherboard is different.
(High speed serial, packetized). Protocol between AMB
and actual memory chips is standard. But AMB to motherboard
is different. Typical usage - Intel server motherboards.
The top two are 2GB max currently. A registered DIMM can allow a doubling or
more, above what unbuffered DIMMs can achieve (as can be seen in the ValueRAM
example document above.) FBDIMMs, since they are buffering, also have the
opportunity to double the module capacity, above what an unbuffered DIMM can do.
I don't know what current technical limits exist, on the AMB to raw chips interfaces
(how many ranks they support).
This Samsung DDR2 document, does promise some larger chips. There are some 2Gigabit
silicon die chips in the pipe, promised Nov.07. They could be used to make a
4GB unbuffered DIMM. On the modules page, a M391T5263AZ(H)3 offers 4GB and has
ECC, and is promised for Dec.07. But I would not hold my breath waiting for
those to show up at Newegg. You'd have a long wait. Some of the stuff listed
in the Samsung documents, never seems to come to retail (maybe it is only used
by OEMs making server products or something - I don't know what the deal is).
http://www.samsung.com/global/busin.../dram/downloads/ddr2_product_guide_oct_07.pdf
(
http://www.samsung.com/global/business/semiconductor/products/dram/Products_DDR2SDRAM.html )
My best guess would be, that four slot GA-MA790FX-DS5 AM2 motherboard is most
likely to yield an 8GB configuration, if you buy what is available today.
This is the supported memory list from Gigabyte.
http://tw.giga-byte.com/FileList/MemorySupport/motherboard_memory_ga-ma790fx-ds5.pdf
Paul
