本帖最后由 stephenmaxmax 于 2012-10-6 13:10 编辑
recc应该是有延迟吧http://www.servethehome.com/unbuffered-registered-ecc-memory-difference-ecc-udimms-rdimms/
Unbuffered ECC versus Registered ECC MemoryAdding to the ECC concept, there are two concepts at play, unbuffered and registered ECC memory modules. The basic difference is that memory commands in unbuffered memory configurations go directly from the controller to the memory module, while in registered memory configurations the commands are sent first to the memory banks’ registers prior to being sent to the modules. This concept may sound difficult, but here is the very simple/ conceptual view regarding what is going on. In the above example the memory controller accesses the memory banks directly. The above assumes that the memory controller resides within the CPU package as it does in modern CPU architectures. Looking at older systems, the memory controller resided within the CPU northbridge. Compare this to the registered memory example below. [size=1.2em]Simple Unbuffered ECC DRAM Model
Here the CPU communicates with the registers for the banks of memory on each module. From there, these registers communicate with the DRAM. The implications of this are twofold. First, on a negative side, instructions take approximately one CPU cycle longer due to the intermediary of the bank register. On the positive side, this buffering reduces the strain on the CPU’s memory controller because it points to the dedicated intermediary register versus accessing the DRAM directly. It is easier on the memory controller to deal with a fewer number of targets. [size=1.2em]Simple Registered ECC DRAM Model
This feature is very important in server scenarios because, for example, an Intel 3400 series platform, such as the Supermicro X8SI6-F or Intel S3420GPLC supports 16GB unbuffered ECC and 32GB registered ECC memory. Likewise, in dual processor systems, such as the E5600 series basedSupermicro X8DTH-6F recently reviewed on ServeTheHome, the delta is much greater with up to 48GB of unregistered ECC or 192GB of registered ECC memory. For virtualization environments where memory, and memory bandwidth is key to achieving high consolidation and density metrics, Registered ECC memory is generally the way to go. If one purchases a server with unregistered ECC DIMMs, then requires additional capacity, then the upgrade operation will require a pull and replace all UDIMM modules making it an expensive proposition.
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发表于 2012-10-5 18:20
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