[hard ten treasures] - 7.2 [dynamic RAM] analysis of the difference between DDR4 and DDR3

Now DDR4 It's very mature , So compared DDR3, What are the more important improvements ？ Let's see ：

1. DDR4 The appearance of the memory module changes significantly , Golden fingers become curved , Easy to unplug and reduce PCB pressure .
2. DDR4 Point to point transfer is used inside the memory , The frequency increases significantly , Up to 4266MHz.
3. DDR4 Memory capacity increased significantly , A single memory can support up to 128GB.
4. DDR4 Power consumption is significantly reduced , The voltage drops to 1.2V、 Even lower .

  DDR3 Memory since 2007 Since service in , It has been through so far 8 A year . comparison Intel In terms of the pace of upgrading , Memory development is quite slow . But fortunately, 2014 end of the year , Major manufacturers have put on the shelves DDR4 Memory products , Take off frequency reaches 2133MHz, Mark the DDR3 The end of the times .

1、DDR4 And DDR3 Memory difference one ： processor

Haswell-E Architecture diagram

   Every time the memory is upgraded , What must be supported is the processor .Haswell-E The memory of the platform is the same as IVB-E/SNB-E It is also designed for four channels ,DDR4 Memory frequency native support 2133MHz, This is compared with IVB-E Of DDR3 Native 1866MHz, The starting frequency has increased a lot .Haswell-E As a new flagship, the two biggest improvements are 6 Nuclear upgrade 8 nucleus , Another point is right DDR4 Support for .

2、DDR4 And DDR3 Memory difference 2 ： Appearance

Card slot difference
  DDR4 The card slot on the module and DDR3 The position of module card slot is different . Both slots are located on the insertion side , but DDR4 The position of the card slot is slightly different , In order to prevent the module from being installed in an incompatible motherboard or platform .

Increase the thickness
   To accommodate more signal layers ,DDR4 Module ratio DDR3 Slightly thick .

DDR4 Golden finger changes a lot
   Pay attention to the above figure , Yuzhan DDR4 The memory golden finger has become bent , Not designed along a straight line , Why on earth is this ？ All the time , Insert the flat memory gold finger into the memory socket , The friction is large , Therefore, the memory is difficult to pull out and insert , To solve this problem ,DDR4 Design the lower part of the memory to protrude slightly in the middle 、 The shape of the edge receding . Transition in a smooth curve between the high point in the center and the low point at both ends . Such a design can ensure DDR4 There are enough contact surfaces between the golden finger of the memory and the memory socket , Signal transmission ensures signal stability at the same time , Let the convex part in the middle and the memory socket generate enough friction to stabilize the memory .

   The location of the interface has also changed , Gold finger in the middle “ The gap ” Position comparison DDR3 Closer to the center . In terms of the number of golden finger contacts , Ordinary DDR4 Memory has 284 individual , and DDR3 It is 240 individual , The spacing of each contact is from 1mm Reduce to 0.85mm.

Curve edge
  DDR4 The module provides curved edges for easy insertion and ease of memory during installation PCB The pressure of the .

3、DDR4 And DDR3 Memory difference three ： Parameters

  DDR4 Of course, the most important mission is to improve frequency and bandwidth .DDR4 Each pin of memory can provide 2Gbps(256MB/s) The bandwidth of the ,DDR4-3200 That's it 51.2GB/s, Than the DDR3-1866 Higher than 70％.

Default frequency DDR4 2133 CL15

DDR4 2133 Bandwidth test under frequency ：48.4GB/s

   From Yuzhan 32GB DDR4-2133 Memory , The default frequency bandwidth alone is as high as 48.4GB/s, so DDR4 Importance to system performance improvement .

   The other is the change of other parameters , Such as capacity and voltage .

  DDR4 In the use of the 3DS After stacking packaging technology , The maximum capacity of a single memory can reach the current product 8 Twice as many . for instance , At present, the common capacity of a single piece of large capacity memory is 8GB（ Single chip 512MB, common 16 star ）, and DDR4 You can achieve 64GB, even to the extent that 128GB. And voltage ,DDR4 Will use 20nm The following process is used to manufacture , Voltage from DDR3 Of 1.5V Reduce to DDR4 Of 1.2V, Mobile version of SO-DIMMD DR4 The voltage will drop even lower .

   The frequency and bandwidth are greatly improved

  DDR4 Each pin of memory can provide 2Gbps(256MB/s) The bandwidth of the ,DDR4-3200 That's it 51.2GB/s, Than the DDR3-1866 Higher than 70％.

   stay DDR In the process of development , Increasing data pre value has always been the main means of performance improvement . But in the DDR4 Time , The increase of data prefetching becomes more difficult , So we launched Bank Group The design of the .

  Bank Group What about the architecture ？ Specifically, each Bank Group You can read and write data independently , In this way, the internal data throughput is greatly improved , It can read a large amount of data at the same time , The equivalent frequency of memory is also greatly improved under this setting .

   stay DDR3 In memory , The connection between memory and memory controller is realized through multipoint branch bus , The characteristic of this design is that once the data transmission volume exceeds the carrying capacity of the channel , No matter how you increase the memory capacity , The performance has been improved a lot .

   therefore ,DDR4 Abandon such a design , Switch to point-to-point bus ： The memory controller can only support one memory per channel . The benefits of this design can greatly simplify the design of memory modules 、 It is easier to reach a higher frequency . however , The problem of point-to-point design is also obvious ： An important factor is that the point-to-point bus can only support one memory per channel , So if DDR4 If the capacity of a single memory is insufficient , It will be difficult to effectively increase the total memory of the system . Of course , This is difficult for developers ,3DS Packaging technology is amplification DDR4 The key technology of capacity .

Capacity surge Up to 128GB

  3DS（3-Dimensional Stack, Three dimensional stacking ） The technology is DDR4 One of the most critical technologies in memory , It is used to increase the capacity of a single chip .

  3DS Technology was first proposed by micron , It is similar to the traditional stack packaging technology , For example, many processors and memories in mobile phone chips are stacked and welded on the motherboard to reduce the volume — The difference between stack welding and stack packaging is , One after chip packaging 、 stay PCB Stack on board ; The other is before chip packaging , Stack inside the chip . Generally speaking , If heat dissipation and process permit , Stacked packaging can greatly reduce the chip area , It is very helpful for the miniaturization of products . stay DDR4 On , Stack packaging is mainly used TSV In the form of silicon perforation .

   The so-called silicon perforation , Just drill holes in silicon wafer by laser or etching , Then fill the metal connecting hole , In this way, the signals between different silicon chips through silicon perforation can be transmitted to each other . In the use of the 3DS After stacking packaging technology , The maximum capacity of a single memory can reach the current product 8 Twice as many . for instance , At present, the common capacity of a single piece of large capacity memory is 8GB（ Single chip 512MB, common 16 star ）, and DDR4 You can achieve 64GB, even to the extent that 128GB.

Lower power consumption Lower voltage

   Lower voltage ： This is every generation DDR An essential element of evolution ,DDR4 Has fallen to 1.2V

   First, let's look at power consumption .DDR4 Memory uses TCSE ( Temperature Compensated Self-Refresh, Temperature compensation self refresh , It is mainly used to reduce the power consumed by the memory chip during self refresh )、TCARtemperature Compensated Auto Refresh, Temperature compensation automatically refreshes , and T CSE similar ）、DBI（Data Bus Inversion, Data bus inversion , For lowering VDDQ electric current , Reduce switching operation ） New technologies such as .

   These technologies can reduce DDR4 Power consumption of memory in use . Of course , As a new generation of memory , The most direct way to reduce power consumption is to use newer processes and lower voltages . at present DDR4 Will use 20nm The following process is used to manufacture , Voltage from DDR3 Of 1.5V Reduce to DDR4 Of 1.2V, Mobile version of SO-DIMMD DR4 The voltage will drop even lower . With the progress of technology 、 Voltage reduction and the combined use of multiple power consumption control technologies ,DDR4 The power consumption performance will be very excellent .

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