Pair of DDR2 DIMM Memory Modules


Double Data Rate DIMM [IIII]

DDR4 is the fourth generation of Double Data Rate memory; however DDR4 is still in the development phase and only exists on paper. The anticipated release dates for DDR4 modules continues to change with each news up-date, but appears to be around 2012 or later. However in 2011 Samsung reported fabricating DDR4 RAM modules, but gave no indication when they might be released. I've also seen reports that indicate DDR4 will not be released for production until 2015.
The initial DDR4 speed grade was reported to be 1.6GHz, but now the numbers are twice that at 2.133Gbps.
As of 2011 there are no PCs that offer DDR4 DIMMs, the faster PCs still come with DDR3 memory.

Double Data Rate Series III DIMMs [DDR-DIMM, or DDR DIMM] utilizes the JEDEC standard for Double Date Rate III [DDR III, DDR3] SDRAM. This page covers DDR3 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 second generation is listed on the DDR2 DIMM page. DDR2 modules may be purchased in one of the following speed grades:

DDR4 Transfer Rate

The initial 1.6GHz DDR4 speed grade is identical to the highest DDR3 speed range.

These are the planed data rates; 1.6GHz (2011), 2.0GHz (2011), 2.4GHz (2012), 3.2GHz (2013)
The estimate for release date (provided after the speed) is for production ramp-up.
[I believe these are JEDEC estimates for dates and may be different for each company that produces the parts]

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]. DDR3 memory represents the third generation in DDR memory. DDR3 begins with a speed grade of 800Mbps as the lowest speed grade. The 800Mbps speed grade is also used as the highest speed grade for DDR II. Here is a Comparison of speed grades.

DDR SDRAM Comparison, showing DDR1, DDR2, and DDR3 speeds

DDR2 Standard

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

DDR4 Electrical Interface

Double Data Rate DDR4 IC's will use 1.2 volt compatible I/O, how ever the supply voltage may be higher.
Laptops may use 1.1v or 1.05 volt supplies for low power operation. For reference see SSTL_15 information.

DDR2 Terminations

DDR3 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, DDR3 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.

DDR4 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. DDR3 provide a 30% reduction in power consumption.

DDR4 Regulators

DDR Voltage Regulator Manufacturers {DDR1 DDR2, DDR3 Voltage Regulators}

As of 2011 only TI makes reference to Low Power DDR3/DDR4 VTT bus termination.

For additional manufacturers refer to the main Voltage Regulator page.

DDR4 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]

As of 2011 there are no companies that produce DDR4 memory DIMMs.

DIMM Sockets;
DIMM/SIMM Socket Manufacturers.

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Modified 1/25/12
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