DUAL ram 1x8 vs 2x4 vs 2x single4

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brianjay0914

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May 5, 2014
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I heard that 2x4 ram is better than 1x8

my question is

what if i buy 2x single 4gb hyper x fury. will it be better than single 1x8gb ram
 
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The catch with buying DIMMs separately is that you have to be certain they are both built exactly the same way to enable full dual-channel operation. Otherwise, you end up in "interleaved" mode instead which is not quite as good or sometimes might not work at all.

This is why buying DIMMs in pair kits is strongly recommended since it eliminates the headaches and pitfalls associated with attempting to match DIMMs after-the-fact if you can no longer get another of the exact same model by the time you need it.
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Titan
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Two identical DIMMs (does not matter if you buy them as a single 2x4GB kit or deparate single 4GB DIMMs but the kits are usually cheaper than singles) = you can run in dual-channel configuration = twice the memory bandwidth vs a single DIMM = better performance.
 
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Tradesman1

Tradesman1

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DUal channel can provide up to a 10-15% performance increase - not double, the memory bandwidth does change when in dual channel it's simply the DRAM is all seen as a single 128 bit device vs the regular 64 bit device that it is it still runs the same i.e. 1600 in single, dual, tri or quad
 
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Titan
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Although it may not translate into anywhere near twice the performance except in extremely bandwidth-intensive algorithms and memory-specific benchmarks, 128bits x 1.6GT/s is still exactly twice the bandwidth as 64bits at the same 1.6GT/s: 25.6GB/s vs 12.8GB/s. It also halves the latency for burst transfers beyond the first word; something people often completely overlook when they looking at DDR4's higher speeds with seemingly horrible timings.

If someone did frame time variance analysis between single-channel and dual-channel, I bet many test scenarios would show improvements far greater than 15%. (Assuming OP's CPU is fast enough for it to matter.)
 
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Tradesman1

Tradesman1

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The freq of the DRAM - say 800 sticks running at DDR (DOUBLE data rate -= effective 1600 runs up to a theoretical max of 12,800 M/Ts a sec, and does this regardless of if it's single 64 bit, dual 128 bit, tri 192 bit, or quad 256 bit channel mode....All DRAM running at the higher bit rate improves performance slightly but nowhere near doubling, tripling, etc - it simply runs much more effectively
 
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Titan
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Looks like you have the wrong definition of what a MT/s is.

MT/s stands for Mega Transitions per second, which is equivalent to megabits per pin. 1600MT/s is 1600MT/s regardless of how wide the bus is, regardless of memory technology and regardless of what the base clock might be. Once you multiply it by the bus width, you get the effective bandwidth in Mbps which you then divide by eight to get MB/s. That 12800MB/s (or 12.8GB/s) figure is PER 64BITS CHANNEL at 1600MT/s.

bandwidth = effective bus width * bit rate

So, doubling the effective bus width (such as by upgrading from having a single DIMM in the system to having one DIMM per channel on a dual-channel board, which practically all mainstream boards have been for over a decade) does double available bandwidth. With a quad-channel architecture like Intel's Extreme chips, available memory bandwidth can be doubled again by populating all four channels since it doubles the effective memory interface width from 128bits for LGA115x to 256bits on LGA2011-*.

Multiplying bandwidth for a given memory technology by raising the effective memory bus width (by adding channels and making individual channels wider) is the whole point behind the progression from single-channel 32bits GPUs to today's multi-channel 512bits-wide high-end GPU memory interfaces.
 
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brianjay0914

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I am now confused by just reading comments haha .


My motherboard is "msi 970 gaming" , so if i buy 1x4gb today and 1x4gb in the other day and put it on the matching slot it'll be dual channel ?
 
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Titan
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The catch with buying DIMMs separately is that you have to be certain they are both built exactly the same way to enable full dual-channel operation. Otherwise, you end up in "interleaved" mode instead which is not quite as good or sometimes might not work at all.

This is why buying DIMMs in pair kits is strongly recommended since it eliminates the headaches and pitfalls associated with attempting to match DIMMs after-the-fact if you can no longer get another of the exact same model by the time you need it.
 
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brianjay0914

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unfortunately there's no dual sticks that is being sold here in my country , you need to buy it in single stick.

so if i buy 2 "Kingston Hyper X Fury 4gb ddr3 1600" (they're sold separately ) it'll function as dual channel ?

 
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brianjay0914

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thanks one more question sir . whats the difference of 1600 , 1866 , 2400 in rams. that does make a difference or it is the compatibility to the motherboard. again my future motherboard is msi970 gaming
 
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Titan
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Memory speed grades beyond 1600MT/s are mostly intended for enthusiasts and overclockers. The rating tells you what maximum speed the manufacturer rated the DIMMs but the highest speed you will be able to use is determined by the weakest link between your memory, CPU and motherboard - if you buy 2133MT/s RAM, put it on a motherboard that is only officially rated for 1833MT/s with a CPU which officially only goes up to 1600MT/s, then the fastest data rate you can officially use is 1600MT/s and anything beyond that would be overclocking.

There is relatively little performance to be gained from pushing memory much beyond 1600-9 so I would get the fastest RAM I can get for little to no extra cost over 1600-9. For every step up in frequency (first number), you can afford about one step up on latency (second number) without worrying about a performance trade-off between the two.
 
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