DDR2 DIMM

Double Data Rate DIMM [II]



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Double Data Rate Series II DIMMs [DDR-DIMM, or DDR DIMM] utilizes the JEDEC standard for Double Date Rate II [DDR II, DDR2] SDRAM. This page covers DDR2 memory modules, which may also be found as SO-DIMM, and Micro-DIMM modules. Fully-Buffered DIMM modules are listed on the FB-DIMM page, refer to the general Memory Module page for a more complete listing of different types of modules, manufactures and descriptions. DDR 'I' [first generation] modules are discussed on the DDR DIMM page. While the third generation is listed on the DDR3 DIMM page. DDR2 modules may be purchased in one of the following speed grades:

DDR2 Transfer Rate

As the name implies, Double Data Rate interfaces provides two data transfers per clock. The clock is differential. The data is registered when the CK goes high [the + side], and /CK goes low [the - side]. DDR2 memory represents the second generation in DDR memory. DDR2 begins with a speed grade of 400MHz as the lowest speed grade. The 400MHz speed grade is also used as the highest speed grade for DDR I. As a side note, it seems that the 400MHz DDR I speed grade actually operates faster then the DDR II 400MHz speed grade ~ due to latencies. The transfer disparity disappears with the DDR2 533MHz speed grade, which operates faster then any DDR 1 speed option. The additional transfer rates used by DDR2 are listed above.

DDR2 Standard

JESD79-2B: DDR2 SDRAM Specification, January 2005
This may not be the latest revision of the DDR-2 standard.

DDR2 Electrical Interface

Double Data Rate II IC's use 1.8 volt SSTL_18 compatible I/O [class II], how ever the supply voltage may be higher.
SSTL-18: Stub Series Terminated Logic for 1.8v [JESD 8-15A]. Class II provides for higher power dissipation, Higher drive and a maximum current of 15.2mA

DDR2 Terminations

DDR2 modules contain the require resistor termination located on the memory chips using a technique called On-Die Termination [ODT]. While DDR1 modules have the necessary resistive termination located on the motherboard. Using ODT, DDR2 are able to reduce the parts count required for mother board while at the same time locate the terminations closer the the signal destination. The ODT termination can be turned on or off by the DRAM controller. Normally the terminations are turned on for Writes and disable for Reads. The value of the ODT termination is selectable based on the number of modules in the system. With one DIMM module the ODT value is set at 150 ohms [300W pull-up and 300W pull-down]. When two modules are loaded into the system the ODT value is changed to 75 ohms [150W pull-up and 150W pull-down] for the DIMM not being written to while the DIMM being accessed has its ODT turned off. Writing to the Extended Mode Register [EMR] controls the ODT presence and value. Three combinations are allowed; termination disabled, 75 ohms, and 150 ohms [ also 50 ohms]. The newest revision adds 50 ohm termination values. ODT improves the eye-diagram over SSTL for either Single-Rank or Dual-Rank modules.

DDR2 Power Dissipation

Power Dissipation for reference only.
A DDR DIMM needs 5.4 watts, a DDR2 DIMM needs 4.4 watts and a DDR2 FB-DIMM needs 10.4 watts

DDR2 regulators

intersil {DDR1 DDR2 Voltage Regulators}

Semtech {DDR1 DDR2 Regulators}

Sipex {DDR1 DDR2 Regulators}

For additional manufacturers refer to the main Voltage Regulator page.

DDR2 DIMM Manufacturers

DDR memory modules are found in desk tops, workstations, and Server applications. Three form factors of DDR are available:
200-pin DDR SODIMM [Notebook computers]
240-pin DDR2 DIMM [DeskTop computers]
240-pin DDR2 FB-DIMM [Servers]

Apacer Inc {240-Pin 1.8v DDR2, ECC/Non-ECC PC2-4200, PC2-5300 Non-ECC 667MHz memory modules}

Centon Electronics {DDR2 DIMM Desktop Memory, PC2-4200, PC2-3200; DDR2 SODIMM, Notebook Memory, PC2-4200 Non-ECC Unbuffered}

Corsair {PC26400, PC2-5400, PC2-4300 DDR2 SDRAM DIMM Module. Module Pairs}

Elpida Memory, Inc. {DDR2 SDRAM DIMM Module}

Integrated Device Technology, Inc. 'IDT' {FB-DIMM memory Module Support}

Infineon {DDR2 SDRAM Components; SO-DIMMs, Registered DDR2 DIMMs, Unbuffered DDR2 DIMMs, Nicro-DIMM DDR2 DIMMs}

Kingmax Inc. {DDRII 800/667/533 Long-DIMM, DDRII 533 Micro-DIMM 214-pin/172-Pin/ECC Unbuffered DIMM, DDRII 400 registered DIMM}

Kingston Technology

Micron {FB-DIMM, DDR2 SDRAM Memory Modules}

Nanya Technology Corp. {240-Pin Unbuffered/fully Buffered/Registered DDR2 DIMM, 200-pin DDR2 SODIMM}

NEC {Memory Modules}

OCZ Technology Inc {DDR2 PC25400/4200, DDR PC2700/3200/3500/4200, Dual Channel}

SMART Modular Technologies {240-Pin DDR2 SDRAM Memory Modules, Registered DIMM, ECC/Non-ECC Unbuffered DIMM, FB-DIMM, 200-Pin DDR2 SDRAM Unbuffered Non-ECC SODIMM}

Viking Components {DDR2 DIMM ECC and Non-ECC Registered and Unbuffered Memory PC2-3200/PC2-4200 256MB to 2G Byte}

Virtium Technology, Inc. {1GB DDR II UB-DIMM, PC2-3200, PC2-4200, PC2-5300}

Unigen {unbuffered, registered 240-pin DIMM or 200-pin SODIMM, which are organized as x64 or x72 high-speed memory arrays}

White Electronic Designs Corporation {DDR2 Modules, DDR Modules, SDRAM Modules, SSRAM, SRAM Modules, Flash Memory Modules}

Wintec Industries Inc. {DDR2 Modules, DIMM Modules, SO-DIMM Modules}

Electronic Engineering Key words for this page: DDR DIMM, DDR2, IC Bus Standard, SSTL, SSTL_18, Integrated Circuit Bus, Chip Bus, Chip-to-Chip Bus, micro-processor [uP] buses, Microcomputer Bus, Microprocessor, Memory Busses, Peripheral chip, Memory, Specification, Spec, Interface, IC, Physical Interface, Description, DIMM, DDR-SDRAM, Pin Outs, Buffer, Advanced Memory Buffer, Manufacturers.

DIMM Sockets; DIMM/SIMM Socket Manufacturers.

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