Date: Mon, 07 Apr 2003 14:09:08 -0400 From: Chuck Swiger <cswiger@mac.com> To: freebsd-questions@freebsd.org Subject: Re: 1GB memory ECC registered vs non-registered Message-ID: <3E91BEC4.9030205@mac.com> In-Reply-To: <DBEIKNMKGOBGNDHAAKGNCELHLLAB.dave@hawk-systems.com> References: <DBEIKNMKGOBGNDHAAKGNCELHLLAB.dave@hawk-systems.com>
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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
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