• BTW your board supports dual channel only in 2-4 and 1-2-3-4 slots according to the manual. With different sticks, like that 8GB and 4GB you've tried, dual-channel won't work. If the above manipulations did not help, try setting the memory to DDR3-1333 or lower and set the timings and voltage according to its SPD spec.
• DDR3’s prefetch buffer width is 8-bit which is double of DDR2. The transfer rate of DDR3 is 800 1600 MT/s. DDR3 operates at a low voltage of 1.5V compared with DDR2’s 1.8V which results in 40% less power consumption. The DDR3 has two added functions namely – ASR (Automatic Self-Refresh) and SRT (Self-Refresh Temperature).
• As a brand of Micron, one of the largest memory manufacturers in the world, Crucial Desktop Memory is the standard for reliable performance. From the original SDRAM technology all the way to DDR4, we’ve engineered the memory technologies that have powered the world’s computers for 40 years and counting.
• 16GB, DDR3 1600/1333/1066 MHz Non-ECC, Un-buffered Memory. Desktop Motherboard B85 DDR3 4th Generation 4 Ram Slots. 6 Month Warranty.

EVGA GeForce GT 640 4GB DDR3 (Single Slot) Overview. Original Series. GeForce GT 640 (GK107 DDR3) Released After.

DDR3L modules are backwards compatible with DDR3 by design.

Manufacturers use the same integrated circuits for DDR3 and DDR3L. The highest quality ICs are tested for operating at 1.35 volts and are branded as DDR3L if they run properly. Other than that, there’s no difference between them.

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yes it is correct, that they should use the same Chips. So from a functionallity point of view it is really just the same compatibility issue as with DDR3 from one vendor to another vendor (or even just for one die shrink to the next die shrink).

JEDEC defines that the DIMM needs to be backward compatible. So if a JEDEC compliant DIMM is operating at 1.5V should be tested and verified from the vendor. But not too many DIMM vendors really state that the DIMM is JEDEC compliant.
E. g. I have seen DIMMs with devices not supporting specific CL that they would need to support to be JEDEC compliant ..

And in this case thre is no need that the DIMM really is backward compatible (even if it is just a question of Speed, or reliability over time).
Even standard DIMMs are theoretically interchangable, there are many compatibility issues between motherboard, controller and DIMM out there .. and DDR3L will not make it better ..

Guess thats the usual difference between theory and praxis ..
and so I prefer to look at the DIMM spec and at least verify that the 1.5V is a supported voltage on a DDR3L DIMM if I intend to use it in a DDR3 System…

Hermann

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.

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 DDR3 (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.

But this does not always translate to better practical performance, as shown in the following video.

AnandTech also ran tests comparing DDR3 and DDR4 and concluded that

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.

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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.

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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.

References