DDR3 SDRAM - Misplaced Pages

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v t e Dynamic random-access memory (DRAM)
Asynchronous	FPM DRAM EDO DRAM
Synchronous	SDRAM DDR SDRAM DDR2 DDR3 DDR4 DDR5 LPDDR (Mobile DDR) Fast Cycle DRAM (FCRAM) eDRAM RLDRAM HBM HBM2 HBM2E HBM3 HBM-PIM HBM3E Hybrid Memory Cube
Graphics	VRAM WRAM MDRAM SGRAM GDDR GDDR2 GDDR3 GDDR4 GDDR5 GDDR6 GDDR7
Rambus	RDRAM XDR DRAM XDR2 DRAM
Memory modules	SIMM DIMM UniDIMM CAMM
Lists	DRAM timeline SDRAM timeline Bandwidth Transistor count

In electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory technology used for high speed storage of the working data of a computer or other digital electronic device.

DDR3 is part of the SDRAM family of technologies and is one of the many DRAM (dynamic random access memory) implementations. DDR3 SDRAM is an improvement over its predecessor, DDR2 SDRAM.

The primary benefit of DDR3 is the ability to run its I/O bus at four times the speed of the memory cells it contains, thus enabling faster bus speeds and higher peak throughput than earlier memory technologies. However, greater bus speed and throughput is achieved at the cost of higher latency. In addition, the DDR3 standard allows for chip capacities of 512 mebibits to 8 gibibits, effectively enabling a maximum memory module size of 16 gibibytes.

Overview

DDR3 memory promises a power consumption reduction of ~17% compared to current commercial DDR2 modules due to DDR3's 1.5 V supply voltage, compared to DDR2's 1.8 V or DDR's 2.5 V. The 1.5 V supply voltage works well with the 90 nm fabrication technology used for most DDR3 chips. Some manufacturers further propose using "dual-gate" transistors to reduce leakage of current.

According to JEDEC the maximum recommended voltage is 1.575 volts and should be considered the absolute maximum when memory stability is the foremost consideration, such as in servers or other mission critical devices. In addition, JEDEC states that memory modules must withstand up to 1.975 volts before incurring permanent damage, although they may not actually function correctly at that level.

The main benefit of DDR3 comes from the higher bandwidth made possible by DDR3's 8 bit deep prefetch buffer, in contrast to DDR2's 4 bit prefetch buffer or DDR's 2 bit buffer.

Theoretically, DDR3 modules can transfer data at the effective clock rate of 800–1600 MHz using both rising and falling edges of a 400–800 MHz I/O clock. In comparision, DDR2's current range of effective data transfer rate is 400–800 MHz using a 200–400 MHz I/O clock, and DDR's range is 200–400 MHz based on a 100–200 MHz I/O clock. To date, the graphics card market has been the driver of such bandwidth requirements, where fast data transfer between framebuffers is required.

DDR3 prototypes were announced in early 2005. Products in the form of motherboards are appearing on the market as of mid- based on Intel's P35 "Bearlake" chipset and memory DIMMs at speeds up to DDR3-1600 (PC3-12800).. AMD's roadmap indicates their own adoption of DDR3 in 2008.

DDR3 DIMMs have 240 pins, the same number as DDR2, and are the same size, but are electrically incompatible and have a different key notch location.

Increased Latencies

In order to increase the speeds of the memory modules with DDR3, it was also necessary to increase the latency of the modules. Latency is the amount of time that it takes for a memory module to process commands in a number of clock or command cycles. The higher the latency, the slower the memory will be at processing a command.

The typical latency for a DDR2 JEDEC standard was 5-5-5-15. The JEDEC standard latencies for the newer DDR3 memory are 7-7-7-15. Even with the increase in the latency for the DDR3 memory, the higher clock speeds allow the memory to still have a greater bandwidth than the older standards. This results in DDR3 memory running at 800MHz to be slightly slower than DDR2 memory that is also running at 800MHz. The real advantage comes when the clock speeds get higher than this mark.

Another thing with the latencies to be aware of is that these are the standards. As manufacturing improves with the memory modules, the modules will be able to run at lower latencies than the JEDEC specifications. It is possible to find DDR2 memory that is faster than the 5-5-5-15 speeds right now. It will take some time for DDR3 to get below the JEDEC latencies.

GDDR3 memory, having a similar name but from an entirely dissimilar technology, has been in use for high-end graphic cards by companies such as NVIDIA and ATI Technologies, and is the graphics system memory on the Sony Playstation 3. GDDR3 has sometimes been incorrectly referred to as "DDR3".

Specification standards

Chips and modules

Standard name	Memory clock	Cycle time	I/O Bus clock	Data transfers per second	Module name	Peak transfer rate
DDR3-800	100 MHz	10 ns	400 MHz	800 Million	PC3-6400	6400 MB/s
DDR3-1066	133 MHz	7.5 ns	533 MHz	1066 Million	PC3-8500	8533 MB/s
DDR3-1333	166 MHz	6 ns	667 MHz	1333 Million	PC3-10600	10667 MB/s
DDR3-1600	200 MHz	5 ns	800 MHz	1600 Million	PC3-12800	12800 MB/s

Features

DDR3 SDRAM Components:

Introduction of asynchronous RESET pin
Support of system level flight time compensation
On-DIMM mirror friendly DRAM pin out
Introduction of CWL (CAS Write Latency) per speed bin
On-die I/O calibration engine
READ and WRITE calibration

DDR3 Modules:

Fly-by command/address/control bus with on-DIMM termination
High precision calibration resistors

Advantages compared to DDR2

Higher bandwidth performance increase, effectively up to 1600 MHz
Performance increase at low power (longer battery life in laptops)
Enhanced low power features
Improved thermal design (cooler)

Disadvantages compared to DDR2

Commonly higher CAS Latency but compensated by higher bandwidth, thereby increasing overall performance
Generally costs much more than equivalent DDR2 memory.