1GB memory ECC registered vs non-registered
cswiger at mac.com
Mon Apr 7 11:09:13 PDT 2003
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.
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