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Friday, March 12, 2010

FB DIMM slots... By the way what is Fully Buffered DIMM (FB DIMM)?

Well, Just got a new Sun SPARC Enterprise T5220 Server & was just reading through the server specs. While reading on it I saw FB DIMM memory slot so to be honest I'm not a very good at Sun hardware knowledge so obliviously I was not aware of what is FB DIMM slot means?

Let's have a tour of introduction on FB DIMM (Fully Buffered DIMM) memory slot.

FB-DIMM (Fully Buffered DIMM) is a memory module technology targeted to servers developed recently created in order to increase the memory speed and the maximum memory capacity of a server.

The main difference between FB-DIMM modules and regular DIMM modules is that on FB-DIMM the communication between the memory controller (chipset) and the module is serial, in the same way that occurs with PCI Express, while on standard DIMM modules this communication is parallel.

Using serial communication the number of wires needed to connect the chipset to the memory module is lower and also allows the creating of more memory channels, what increases memory performance. With FB-DIMM technology it is possible to have up to eight modules per channel and up to six memory channels. So this technology increases both memory capacity and speed.

Another important aspect of FB-DIMM is that it uses different paths for data transmission and data reception. Standard DIMM modules use the same path to both transmit and receive data. So DIMM is like a road with two-way traffic so more chances of traffic jam or some times collision however FB-DIMM is like a one-way road so smooth & super fast traffic & almost no chances of collision.

The system used on FB-DIMM modules helps to increase the performance of the memory subsystem.

So the bottom line is using FB-DIMM slots we can get greater memory capacity and higher performance.

Some of the implementation of Fully Buffered DIMM are as follows -

• Sun Microsystems is using FB-DIMMs for the Niagara II (UltraSparc T2) server processor. Few server that I know -

Sun SPARC Enterprise T5220 Server
Sun SPARC Enterprise T5140 Server
Sun SPARC Enterprise T5240 Server
Sun SPARC Enterprise T5440 Server
• Intel has adopted the technology for their newer Xeon 5000/5100 series and beyond, which they consider "a long-term strategic direction for servers".
• Intel's enthusiast system platform Skulltrail uses FB-DIMMs for their dual CPU socket, multi-GPU system
• Some of the HP ProLiant servers


  1. Thanks for the post, we just got "Sun SPARC Enterprise T5140 Server" we are facing wrong memory size reporting in solaris 10, i am not sure if you have faced the same?


  2. Hey guys,

    does it matter which DDR2 ram memory i put on my motherboard?
    for example i saw this 4GB KIT 2X2GB PC2-5300 240 PIN DDR2 667MHZ FULLY BUFFERED (FB-DIMMs) RAM MEMORY... does it matter if its FB-DIMMs or a regular DDR2 DIMMs? because i dont want to make a mistake and screw up my computer.. i just want my computer to run faster as i expect..i just dont know which memory i should buy.. by the way my motherboard is:



    Thnx in advance...