Based on performance, DDR4 SDRAM has both an advantage and a disadvantage versus DDR3.
On the advantage front, DDR4 can handle somewhat more "mega transactions per second" (aka MT/s) than DDR3. MT/s is the measure of the memory's ability to crunch binary integers.
On the other hand, DDR4 nonintuitively has as much as 50% more latency for "column addressable strobe" (CAS) than DDR3. CAS latency is the amount of time it takes from the memory controller asking for a specific memory column on a random access module to when that data is comes out of that module.
In the real world, it means that applications crunching large, uncompressed files such as video editing files will notice a marginally better performance when running on DDR4. However, applications that are heavier on transactions will experience a noticeable latency-related performance edge when running on DDR3. Expect DDR4 manufacturers to tighten that CAS latency difference up over future releases.
For the gamers out there, neither DDR4 nor DDR3 has much of an impact on performance. Game performance is most affected and improved by graphics chips and controllers.
There are a few additional compelling differences. DDR4 DIMMs consume 20% less power than DDR3 DIMMs (1.2V vs. 1.5V). That power difference can be a huge power and cooling financial savings when there are hundreds or thousands of servers with dozens of DIMMs each. It also reduces backup power requirements for batteries or super capacitors and floor space -- saving even more money.
DDR4 SDRAM has a lot more bandwidth than DDR3. That difference will become more noticeable in future multicore CPU releases by Intel, AMD, ARM, and Oracle/Fujitsu that can and will take advantage of the additional memory channel bandwidth. The current CPUs in the market don't yet take advantage of that bandwidth.
DDR4 has the potential for doubling the DIMM density vs. DDR3. This is a ways out in the future, but once again has significant implications in DIMM slot utilization, power, cooling, rack space and floor space.
DDR3 is currently significantly lower-priced than DDR4. Street prices have been reported to be as much as a third lower than prices for equivalent DDR4 capacities. DDR4 is still pretty new to the market, and volumes do not match DDR3. Expect that price curve to flip in the future.
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