Hi Sidney, Your question is a little broad, not sure if you have a specific memory technology or application in mind (e.g. SDRAM, DDR1, etc.) but the basics are the same. However, the differences in module types aren't too tricky. First, the term buffered and registered, with respect to modules, are the same thing. There are unbuffered DIMMs and Registered DIMMs. The term "buffered" is not generally used (to my knowledge) when referring to DIMMs. Yes, it's strange to have an unbuffered DIMM and not a buffered DIMM, but that is the terminology chosen. The most significant difference between unbuffered and registered DIMMs are that the command/address and control signal groups are "registered" on a Registered DIMM. That is to say, they are driven from the memory controller to a register on the DIMM that re-drives the signals to the DRAM devices on the module. Also, the clock signals are driven to a PLL on the registered DIMM and then fanned out to the DRAM devices. The primary benefit of this scheme is a reduction in the number of DRAM inputs (i.e. think capacitive loading) that the memory controller must drive directly. This is pretty much required for the memory densities necessary in server/workstation systems these days. One of the down sides of this is an increase in latency as compared to the unbuffered DIMM. Generally, you must suffer a roughly 1 clock cycle latency for command/address and control to move through the register (don't quote me on the exact latency, check data sheets/specs). Conversely, unbuffered DIMMs do not have any registers on the modules. All signal groups are simply driven directly from the memory controller to the DRAM devices on the module. This means the I/O cells on the memory controller must be able to properly drive the maximum amount of memory loads you would need to support in your system design (i.e. timing, signal integrity requirements, etc.) Also, note that the data signals (as well as strobes and data mask) are driven directly to the DRAM devices on the module for both unbuffered or registered, no significant differences. However, in general the data I/O drivers usually drive a significantly lower number of DRAM inputs than address/command and control. Example of loading difference: using unbuffered DIMMs with x8 DRAM devices and having two slots would require your address/cmd signals to drive a possible maximum load of 32 DRAM inputs (assuming one copy of address signals, no ECC and double sided modules) However, with registered DIMMs you could reduce the load on your address bus (from the controller's view) to basically four register inputs (i.e. two per module or slot). This is a very general example and is simply meant to illustrate possible loading scenarios. Hope this is helpful. I'm sure others will answer as well. Also, you can talk with your friendly neighborhood memory vendor apps engineer for more details. Regards, Jim P. Jim Pankratz Dell Client Signal Integrity Group 512.723.5357 jim_pankratz@xxxxxxxx -----Original Message----- From: Sidney S [mailto:sidney16481@xxxxxxxxx] Sent: Friday, October 31, 2003 7:23 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Question on DIMM's Hello, Could anybody provide more info on unbuffered , buffered, registered DIMM's?? What are the differences and advantages and disadvantages of each? Thanks, Sidney --------------------------------- Do you Yahoo!? Exclusive Video Premiere - Britney Spears ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu