DDR3 vs. DDR4

The two biggest drivers of speed for a PC are storage (SSDs vs. hard drives) and RAM. More RAM improves PC performance, not just for hardcore applications like games but also more common apps like web browsers. DDR3 was a giant leap over its predecessor DDR2, and this comparison looks at whether that is true for DDR4 as well.

The DDR4 standard offers higher module density, better reliability, higher transfer rates and decreased voltage thereby providing increased speed and better power efficiency. It is also a standard designed with the future in mind; e.g., it supports 3D stacking of dies with through-silicon-vias (TSVs) which allows increasing module density by stacking up to 8 dies. But in practice users may not experience a noticeable difference in performance when using DDR4 RAM modules available today.

Comparison chart

VOLTAGE 1.5 Volts (standard); 1.65 Volts (high performance); 1.35 V (low voltage) 1.2 Volts (standard); 1.35 V (high performance); 1.05 V (low voltage) SPEED 800 Mhz, 1066 Mhz, 1333 Mhz, 1600 Mhz and 1866 Mhz 800 Mhz, 1600 Mhz, 2133 Mhz MODULES 240-pin DIMM (same size as DDR2 but are electrically incompatible with DDR2 DIMMs and have a different key notch location). DDR3 SO-DIMMs have 204 pins. 288-pin DIMMs but similar in size to 240-pin DDR3 DIMMs. DDR4 SO-DIMMs have 260 pins. PREFETCH BUFFER 8n 8n BUS CLOCK 400-1066 MHz 1066-2133 MHz INTERNAL RATE 100-266 MHz 100-266 MHz TRANSFER RATE 0.80-2.13 GT/s (gigatransfers per second) 2.13-4.26 GT/s (gigatransfers per second) CHANNEL BANDWIDTH 6.40-17.0 GBps 12.80-25.60 GBps RELEASE DATE 2007 September 2012

Is DDR4 backwards compatible?

DDR4 is not backward compatible with DDR3 motherboards because the physical design of modules (DIMMs) for DDR4 and DDR3 are different.

Spot the difference: schematic of the physical design of DDR2, DDR3 and DDR4 DIMMs.

DDR4 vs DDR3 DIMMs
DDR3 modules use 240 pins and DDR4 DIMMs use 288 pins. Both DDR3 and DDR4 DIMMs are 5¼ inch (133.35 mm) in length but the pins in DDR4 are spaced closer (0.85mm) than DDR4 (1mm).

They are also different in height and thickness — the increased height of DDR4 modules (31.25mm instead of DDR3's 30.35mm) makes signal routing easier, and the increased thickness (1.2mm vs. DDR3's 1mm) accommodates more signal layers.

The position of the notch on DDR4 memory modules is also different from DDR3 modules. This prevents accidental insertion of the wrong type of memory because they are not backward compatible.

Module Density
The DDR4 standard allows for DIMMs of up to 64 GiB in capacity, compared to DDR3's maximum of 16 GiB per DIMM.

Speed
DDR4 is designed for transfer rates of 2.13 to 4.26 GT/s, which is significantly higher than DDR3's transfer rates of 0.8 to 2.13 GT/s.

DIMM Type Data Rate Module Name Peak Transfer Rate DDR4-2133 2133 MT/s PC4-17000 17064 MB/s DDR4-2400 2400 MT/s PC4-19200 19200 MB/s DDR4-2666 2600 MT/s PC4-20800 20800 MB/s DDR4-2800 2800 MT/s PC4-22400 22400 MB/s DDR4-3000 3000 MT/s PC4-24000 24000 MB/s DDR4-3200 3200 MT/s PC4-25600 25600 MB/s

Overall, comparing DDR4 to DDR3, there is little difference to separate the two. In a couple of small instances one is better than the other, but on those edge cases it might be prudent to say that we cannot make a final decision until we can synchronize the rest of the system, such as the size of CPU caches. When we can perform such tests, we will run some more numbers.

Technical Features
JEDEC, the organization that designs DDR standards lists some technical features of DDR4 on their website:

Three data width offerings: x4, x8 and x16
New JEDEC POD12 (1.2V) interface standard for DDR4
Differential signaling for the clock and strobes
Nominal and dynamic ODT: Improvements to the ODT protocol and a new Park Mode allow for a nominal termination and dynamic write termination without having to drive the ODT pin
Burst length of 8 and burst chop of 4
Data masking
DBI: to help reduce power consumption and improve data signal integrity, this feature informs the DRAM as to whether the true or inverted data should be stored
512 K page size for x4 devices: reduces power (less activation power), and extends the usefulness of x4 devices, which allow for more efficient EDC solutions for high-end systems
Programmable refresh: Reducing performance penalty of dense DDR4 devices by allowing for refresh intervals ranging from 1x to .0625x the normal refresh interval
CRC computation/validation across the data bus: Enabling error detection capability for data transfers – especially beneficial during write operations and in non-ECC memory applications
New CA parity for command/address bus: Providing a low-cost method (parity) to verify the integrity of command and address transfers over a link, for all operations
Per-DRAM Addressability: Can uniquely select and program DRAMs within a memory structure
DLL off mode supported

Cost and Market Share

DDR4 adoption has been much slower than DDR3. Prices for DDR4 memory modules have not fallen with mass adoption, so the DIMMs continue to be more expensive compared with DDR3 modules.

Internet search interest for DDR4 (red) and DDR3 (blue line) from July 2014 to July 2017 as reported by Google Trends.

Search trends also reveal that as of August 2017, DDR3 memory continues to be more popular worldwide.

DDR3 or DDR4: Which one should I choose?

For most consumers the choice will be simple because DDR4 is not backward compatible. If your motherboard was designed for DDR3, then that's what you can choose. Even if you're setting up a new PC, you will still choose based on the other components — the CPU and motherboard — of the system.

Some of the latest CPUs from both Intel and AMD support DDR4 SDRAM and some are still designed for DDR3. DDR4 would have been a good way to future-proof a new PC but chances are DDR3 will continue to be in wide use for the next 3-5 years at least. And future gains in DDR4 performance probably won't benefit current systems because the clock speeds won't match.