Different Types of RAM's

DDR3 SDRAM
Double data rate type three SDRAM (DDR3 SDRAM) is a type of synchronous dynamic random-access memory (SDRAM) with a high bandwidth ("double data rate") interface, and has been in use since 2007. It is the higher-speed successor to DDR and DDR2 and predecessor to DDR4 synchronous dynamic random-access memory (SDRAM) chips. DDR3 SDRAM is neither forward nor backward compatible with any earlier type of random-access memory (RAM) because of different signaling voltages, timings, and other factors.

Generally the question arises what is the difference between DDR3 and DDR3L?

The difference between these two RAMs is nothing but the voltage consumption. The DDR3L RAM consumes lesser voltage compared to the DDR3. This reduces heating and enables faster operation.
DDR3L RAMs will be compatible only on latest 3rd generation processors.

DDR4
The final specification of DDR4 DRAM, which will help PCs run faster through more power-efficient data transfers, was published Tuesday.

DDR4 memory shuffles data faster than DDR3 memory, which is in most new computers available today. The new memory type implements a new process to read, write and refresh data more efficiently, and the improved throughput boosts application performance by transferring information to storage and memory faster.
The new memory type will be used in servers, PCs and mobile devices. The specification was finalized by the JEDEC Solid State Technology Association, which has led DRAM development for decades.
Top DRAM makers like Samsung, Micron and Nanya have already started shipping test units of the memory. Integrated Device Technology two weeks ago announced it was shipping test units of DDR4 memory with error correction features, which typically go into servers.
The proposed transfer speed of DDR4 is expected to top off at 3.2 gigatransfers per second, while JEDEC has said that DDR3 exceeded its expected maximum speed of 1.6 gigatransfers per second. DDR4 DRAM will consume 1.2 volts, compared to 1.5 volts for DDR3. The memory bus speed will start at 2133MHz, which is a boost from the average bus speed of 1333MHz and 1666MHz for DDR3.

Difference between DDR3 and DDR4

DDR4 operates at a lower voltage than DDR3. DDR4 runs at 1.2 volts, down from 1.5. It doesn't sound like much, and it's really not for your typical home PC. Most Haswell-E desktop systems (where you'll most often see DDR4 in use) will operate somewhere in the 300W to 1200W range. The voltage difference for those numbers might account for a 15W savings over DDR3—not a lot for a home user. But for server farms and other large-scale computer architectures, where you could have hundreds of systems running thousands of DDR4 modules, that 15W difference adds up.

Another big difference between DDR3 and DDR4 is speed. DDR3 specifications started at 800 MT/s (or Millions of Transfers per second) and some went as high as 2133. DDR4, meanwhile, starts at 2133 MHz. The increased speed means an overall increase in bandwidth.
This unfortunately comes with an increase in latency as well, but the increased clock speed makes for quicker transfers while maintaining an overall latency comparable to DDR2 and DDR3. DDR3-1600 operated at a latency of CL11, which took 13.75 nanoseconds to initiate a read. DDR4-2133 sits at CL15 and performed a read at 14.06 nanoseconds—only a 2% increase.

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