DIMM Memory Modules


Fully-Buffered DIMM

FB-DIMM Description

Fully-Buffered Double Data Rate Synchronous DRAM Dual In-Line Memory Module:
Fully-Buffered DIMM [FB-DIMM, or FBDIMM] utilizes the JEDEC standard for Double Date Rate2 [DDR II] SDRAM. This page covers the FB-DIMM modules, refer to the general Memory Module page for a more complete listing of different types of modules, manufactures and descriptions. FB-DIMM modules are Fully-Buffered [on-board] at the high-speed Advanced Memory Buffer (AMB). Unlike normal DIMM modules which are connected in parallel to the memory controller [off a stub], FBDIMM modules are connected in a point-to-point serial architecture. The 'first' on-board buffer [AMB] provides a bi-directional interconnect to the memory controller [northbound] on the motherboard, and a different bi-directional interconnect to the next DIMM in the bank [southbound]. The second FB-DIMM connects to the first DIMM [northbound] and the next one in the chain [southbound] . A maximum of eight DIMMs may be connected using the FBDIMM approach. Each FBDIMM in the bank receives its own clock line from a common clock source. The FB-DIMM modules may also reside on a memory riser card, but a repeater may be required. The southbound lanes consist of 10 differential lines [2 x 10], while the northbound lanes consist of 14 differential lines [2 x 14]

FB-DIMM System Memory Module Bank

FB-DIMM memory modules use the SMBus for 100kHz communication with the AMB configuration registers [as a slave]. The SMbus interface is independent of the FBDIMM link. Address and data is transmitted as a differential [800mv] point-to-point signal on a 50 W terminated line. The clock runs through the FB-DIMM and is terminated on the motherboard. The HCSL [High Speed Current Steering Logic] clock runs at 1/4 the DDR2 DRAM frequency [133, 166, and 200MHz]. The power supply is 1.5 volts.

DDR2 Power Dissipation

I found this text on the web about power dissipation but have yet to verify it.
A DDR DIMM requires 5.4 watts, a DDR2 DIMM needs 4.4 watts and a DDR2 FB-DIMM requires near 10.4 watt.

FBDIMM Physical Size

FB-DIMM are currently produced in speeds of PC2-4200, PC2-5300, and PC2-6400. Transmission rates for the 'PC2-xx' series of devices:
PC2-4200 (DDR2-533 SDRAM); Clock Speed: 266MHz, Data Rate: 533MHz, Through-put 4200MB/s
PC2-5300 (DDR2-667 SDRAM); Clock Speed: 333MHz, Data Rate: 663MHz, Through-put 5300MB/s
PC2-6400 (DDR2-800 SDRAM); Clock Speed: 400MHz, Data Rate: 800MHz, Through-put 6400MB/s

240 Pin FB-DIMM Memory Module

The physical size of the FBDIMM stick is 133.5mm x 30.5mm, at 240 fingers. The notch {key} is 8mm right of center [or 74.68mm from left side], which differs from Registered DIMM modules at 4mm right of center. The FB-DIMM pin out is listed on the FBDIMM Pinout page.


Eye Diagram, Tx

FB-DIMM Tx Jitter
Transfer Rate UI Nom TTx-Total-min TTX-Eye-Median-Max-Jitter
(Gbps) (ps) (ps) (ps)
3.2 312.0 248.5 32.0
4.0 250.0 191.0 29.5
4.8 208.0 157.0 25.68

Eye Diagram, Rx

FB-DIMM Rx Jitter
Transfer Rate UI Nom TRX-Total Min TRX-EYE-Median-Max-Jitter VRX-DIFF p-p-MIN
(Gbps) (ps) (ps) (ps) (mV)
3.2 312.0 115 98.67 170
4.0 250.0 90 80 170
4.8 208.0 75 66.68 170

FB-DIMM Speed offerings include 533Mbps [DDR2-533], 667Mbps [DDR2-667], and 800Mbps [DDR2-800].

The electrical interfaces used by memory modules which include LVTTL, SSTL, and HSTL and others are listed on the IC Bus page. Memory chips/ Memory IC manufacturers are listed on the Memory IC page.

AMB Interface IC Manufacturers

The Advanced Memory Buffer [AMB] chip is the memory module's interface between the mother board memory controller IC and all other FB-DIMM modules on the motherboard.

IDT {Advanced Memory Buffer (AMB) device Supports DDR2-533, DDR2-667, DDR2-800 memory}

Renesas {Advanced Memory Buffer (AMB) SDRAM interface connects to DDR2-533, DDR2-667 and DDR2-800 devices}

FBDIMM Manufacturers

Server applications implement FB-DIMM modules because of their requirement for large amounts of memory.
FB-DIMM modules are not found in desktops because of the high cost of the modules.
However FB-DIMM memory may be found in some high-end workstations.
Both Road-Maps from AMD and Intel show that FB-DIMMs are being dropped from all but a few server lines as of 2007.

Centon Electronics {PC2-4200F; 512MB Fully Buffered DIMM DDR2 ECC SDRAM Memory module is 67,108,864words by 72bit 240-pin Dual In-line Memory Module(DIMM), assembled with 9 pieces of a 64MX8bit DDR2 SDRAM in FBGA package}

Hynix Semiconductor America Inc. {512MB, 1GB and 2GB density FB-DIMM}


Micron Technology, Inc {Single-rank / Dual-rank, x8-based, PC2-4200/PC2-5300}

Super Talent Technology {DDR2 FB DIMMs to 4GB; PC2-4300, PC2-5300, PC2-6400}

DIMM Sockets; DIMM/SIMM Socket Manufacturers.

Leroy's Web Page

Electronic Parts and Equipment Distributors Electronic Component Manufacturers OEM Electronic Equipment Manufacturers EDA Software Producers CAD/CAE Software Engineering Standards, EE Publications Interface/Embedded Computer Bus Electronic Engineering Design Data Engineering Reference Information.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 1/28/12
Copyright © 1998 - 2012 All rights reserved Leroy Davis