1GB memory ECC registered vs non-registered

[Chuck Swiger]

Dave [Hawk-Systems] wrote:
> Currently have some ISP1100 rackmount servers with 512k ECC unregistered PC100
> RAM in them.  In preparing to pick up more memory to boost these little boxes up
> to 1GB of RAM each, a memory company rep indicated that unregistered ECC would
> work fine up to 512mb, but if we moved to 1GB of memory then we would have to
> switch all memory over to registered ECC or we would run into problems...

Basicly, registered memory has extra buffer chips and a PLL that 
regenerates the address being accessed to the SDRAM chips in sync with 
the clock.  This adds a wait state, I think, but lets the DIMM burst 
data faster once it gets going-- I remember a timing for PC66 or PC100 
SDRAM that goes from 5-2-2-2 (11 clocks) to 6-1-1-1 (9 clocks) or some 
such.  That's if the MB supports the /REGE pin, of course.

Regardless, the point is that registered memory provides much better 
timing tolerances compared to unregistered memory, and the buffering 
helps drive a stronger signal to the motherboard.  If these motherboards 
  have marginal or inadequate buffering to handle larger DIMMs for 
themselves, they'll need to use buffered/registered RAM or risk data 
corruption when you fill 'em up with lots of memory.

Does your MB have three DIMM slots or four?  MB's with four DIMM slots 
tend to have buffering between RAM and the northbridge, and thus are 
more stable; motherboards with three DIMM slots tend to not have any 
extra buffering and are more marginal when you fill 'em up with RAM.

-Chuck