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what is the difference between DDR3 RAM and DDR2 RAM?

Posted on 2014-01-05
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Last Modified: 2014-01-07
Hello and Good Afternoon Everyone,

           Recently, I purchased an Acer Aspire 17.3" laptop with a fairly impressive hardware makeup.  With respect to the hardware makeup, I did notice the 6GB of RAM to be referred to as DDR3 RAM which brings me to the point of my question.  What is the difference between DDR3 RAM and DDR2 RAM?  From a previously closed post, I think I understand that DDR2 RAM reads and writes data 2 times at each cycle of activity.  I am still unclear with respect to exactly what that means though.  Perhaps the DDR3 RAM is a newer generation of RAM as compared to DDR2 RAM, thus, making it faster because of having greater databandwidth.  I assume DDR3 RAM uses a larger bus on the board for data transport too as compared to DDR2 RAM.  Of course, all of these personal conclusions are based on speculation or guess work at best.  With that in mind, if someone could reflect upon this question and share some insights to it, I will greatly appreciate it.  

               In the meantime, I will look forward to reviewing everyones feedback.

              Thank you

               George
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Question by:GMartin
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Netflo earned 250 total points
ID: 39757963
Your answer is here: http://en.wikipedia.org/wiki/DDR3_SDRAM

The primary benefit of DDR3 SDRAM over its immediate predecessor, DDR2 SDRAM, is its ability to transfer data at twice the rate (eight times the speed of its internal memory arrays), enabling higher bandwidth or peak data rates.

Compared to DDR2 memory, DDR3 memory uses 30% less power. This reduction comes from the difference in supply voltages: 1.8 V or 2.5 V for DDR2, and 1.5 V for DDR3. The 1.5 V supply voltage works well with the 90 nanometer fabrication technology used in the original DDR3 chips. Some manufacturers further propose using "dual-gate" transistors to reduce leakage of current.[1]
According to JEDEC,[2] 1.575 volts 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 are not required to function correctly at that level.
Another benefit is its prefetch buffer, which is 8-burst-deep. In contrast, the prefetch buffer of DDR2 is 4-burst-deep, and the prefetch buffer of DDR is 2-burst-deep. This advantage is an enabling technology in DDR3's transfer speed.
DDR3 modules can transfer data at a rate of 800–2133 MT/s using both rising and falling edges of a 400–1066 MHz I/O clock. Sometimes, a vendor may misleadingly advertise the I/O clock rate by labeling the MT/s as MHz. The MT/s is normally twice that of MHz by double sampling, one on the rising clock edge, and the other, on the falling. In comparison, DDR2's current range of data transfer rates is 400–1066 MT/s using a 200–533 MHz I/O clock, and DDR's range is 200–400 MT/s based on a 100–200 MHz I/O clock. High-performance graphics was an initial driver of such bandwidth requirements, where high bandwidth data transfer between framebuffers is required.
DDR3 does use the same electric signaling standard as DDR and DDR2, Stub Series Terminated Logic, albeit at different timings and voltages. Specifically, DDR3 uses SSTL_15.[3]
DDR3 prototypes were announced in early 2005. Products in the form of motherboards appeared on the market in June 2007[4] based on Intel's P35 "Bearlake" chipset with DIMMs at bandwidths up to DDR3-1600 (PC3-12800).[5] The Intel Core i7, released in November 2008, connects directly to memory rather than via a chipset. The Core i7 supports only DDR3. AMD's first socket AM3 Phenom II X4 processors, released in February 2009, were their first to support DDR3.
DDR3 DIMMs have 240 pins and are electrically incompatible with DDR2. A key notch—located differently in DDR2 and DDR3 DIMMs—prevents accidentally interchanging them. Not only are they keyed differently, but DDR2 has rounded notches on the side and the DDR3 modules have square notches on the side. [6] DDR3 SO-DIMMs have 204 pins.[7]
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by:garycase
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Hi George,

As you've already surmised, DDR3 is just the next evolution in the architecture of synchronous RAM chips used in PC's.     As noted above, it can run at twice the speed internally of DDR2 modules; although DDR3 modules don't have nearly double the transfer speed of DDR2 modules due to higher latency requirements.

In addition to the speed improvement, the lower operating voltage is a nice improvement that reduces the power requirements and thus allows the modules to run somewhat cooler than their predecessors.

Newer systems this year are likely to use DDR4 (the next evolution of this technology) ... which graphics cards have been using for some time (they use the higher bandwidth much more efficiently than the CPU can due to the high number of parallel operations).    In fact, some graphics cards already use DDR5 !!
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by:Darr247
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ID: 39758301
> I assume DDR3 RAM uses a larger bus on the board for data transport
> too as compared to DDR2 RAM.

That would not be a correct assumption. A full size (as opposed to SODIMM) DDR3 stick fits in the same 240-pin "slot" as Double Data Rate 2 (DDR2) RAM, but the sockets have a key (and the RAM sticks a keyway) that is in a different location so they can not be inserted in the wrong type of slot (that's also what keeps you from inserting them backwards, or turned 180 degrees from correct).  DDR3 effectively has a larger amount of bandwidth, but the bus size is the same.
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by:garycase
garycase earned 200 total points
ID: 39758319
Darr247 is essentially correct that there's not a larger bus used for DDR3 vs. DDR2 modules;  but it IS true that the DDR3 modules in your new laptop have 4 additional pins that are used for additional grounding.    Since it's a laptop, you're using 204-pin SODIMM modules, as opposed to 200-pin DDR2 SODIMMs.    With desktops, Darr is correct that both DDR2 and DDR3 modules have 240 pins -- but for a laptop there is indeed a 2% larger bus for the DDR3 modules.
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Author Comment

by:GMartin
ID: 39764021
Hello and Good Evening Everyone,

              Thanks so much for giving a technical breakdown of the differences between DDR3 and DDR2 RAM.  All points brought up did make sense and certainly explains why DDR3 RAM is more appealing on the current market especially when one looks at current systems rather they be desktops or laptops.  While I certainly appreciate the informative feedback given in addtion to the correction made on some of my assumptions, I especially thank Gary Case for giving brief comments about DDR4 RAM.  As I have noticed from all of Gary's past feedback given to many of my questions, he never fails to provide a simple breakdown to tough and complicated topics by tying one thing into another.  For example,  I thought it was a good touch when he brought up the point that DDR RAM has already been used on video cards and has been for some time.  Each and everytime this approach to feedback is taken,  I get a wider view or perspective of the answers given.  In other words, it allows an escape from what I commonly refer to as "tunnel vision".  Whether it be a technical topic such as the one posted or a common, day to day personal matter, I believe it is always a good idea to see the whole picture of things.  While I certainly can not speak for every user of EE, I must say this is one lesson this forum has and continues to teach me.  

                Have a great night everyone.  As always, thank you so much for broadening my thinking on this and other matters.  Your influence is always noticed and appreciated.  

                 Thank you

                George
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