During the second half of last year, Intel introduced the Haswell-E CPU series, and along with it, the first processor platform to support DDR4 memory. Plenty of time for us to compare a number of DDR4 memory kits. We put eight of them to the test.
The new DDR4 memory type has been engineered to operate at lower voltages and to (in the long run) operate at much higher clock frequencies than DDR3. The first official DDR4 standard, which is of course supported by Intel's Haswell-E series of CPUs, operates at 2133 MHz. While there obviously are quite a few DDR3 memory kits that offer speeds of 2133 MHz (and up), you should keep in mind that this is just the baseline for DDR4. Various DDR4 memory kits that guarantee speeds of over 3 GHz are already available for purchase, and we wouldn't be surprised if we end up breaching the 4 GHz barrier down the road.
The higher clock frequencies of DDR4 do result in higher default latencies, just as was the case during the transition from DDR to DDR2 and from DDR2 to DDR3. The memory kits in our test sample have CAS latencies of 13, 15, or even 16 clock cycles, where latencies of 9, 10, or 11 cycles would be the norm for DDR3-2133 modules. You could thus conclude that given identical clock frequencies, DDR4 memory will be slightly slower than DDR3 memory, and that the primary advantage of DDR4 is that we'll eventually be able to reach much higher clock frequencies. That said, a number of adjustments to the way in which DDR4 memory is controlled do already compensate for most of the performance loss.
An immediate advantage of DDR4 is the lower voltage and the corresponding reduction in power consumption. DDR4 modules use a default voltage of 1.2V (or 1.35V for kits with very high clocks), whereas 1.5V (or 1.65V for high-end kits) is the norm for DDR3. While a modest reduction in power consumption might not matter much for a high-end Haswell-E desktop, users of regular desktops, laptops, and tablets will certainly appreciate it. Furthermore, saving over a watt per module will certainly be noticed in the server world, where server racks can contain hundreds of memory modules.
DDR4 memory modules have the same length as DDR3 modules. However, they do feature more pins (284 as opposed to 240), and the central notch is located in a different spot. As a result, it is impossible to accidentally insert a DDR4 module into a DDR3 slot or vice versa.