Because laptops have limited upgrade potential I think they want to leave the other slot free so the user can expand without having to partially remove existing. If custom configured I think many companies allow the option of dual channel vs single.
In my personal laptop it came with 1x8GB module. I put in another one taken from a deceased laptop, gives a nice boost. Modules are mismatched but still give dual channel operation (2400 single rank + 2133 dual rank!). 
With quad channel RAM, how much faster percentage wise is LL world record crunching on Skylake X vs some thing like Coffee Lake?

[QUOTE=simon389;498854]With quad channel RAM, how much faster percentage wise is LL world record crunching on Skylake X vs some thing like Coffee Lake?[/QUOTE]
Depends on RAM speed, ranks, core speed, and core count. But given that RAM is usually the bottleneck, double the RAM should give about double the throughput with double the cores. The best value is still the low cost quad core systems with fast dual rank RAM: it's cheaper to build two quad core systems than one octocore system with quad channel RAM due to motherboard and CPU costs. 
[QUOTE=Mark Rose;498930]it's cheaper to build two quad core systems than one octocore system with quad channel RAM due to motherboard and CPU costs.[/QUOTE]To [i]build[/i], okay. To [i]run[/i]? Don't forget about the electricity cost. If you run it 24/7 at 100% then those costs add up. It's double for two systems.

[QUOTE=retina;498954]To [i]build[/i], okay. To [i]run[/i]? Don't forget about the electricity cost. If you run it 24/7 at 100% then those costs add up. It's double for two systems.[/QUOTE]
Actually SkylakeX burns more than twice as much electricity as two of my 4core systems. 
Strange benchmark scores
A few RAM benchmarks of interest:
[B]OLD i5 4690K @ stock 3.5Ghz with 16GB (4GBx4) 2400Mhz DDR3 RAM[/B] Timings for 2048K FFT length (4 cores, 1 worker): 4.35 ms. Throughput: 230.05 iter/sec. Timings for 2304K FFT length (4 cores, 1 worker): 4.78 ms. Throughput: 209.00 iter/sec. Timings for 2400K FFT length (4 cores, 1 worker): 4.90 ms. Throughput: 203.89 iter/sec Timings for 2560K FFT length (4 cores, 1 worker): 5.21 ms. Throughput: 191.78 iter/sec. Timings for 2688K FFT length (4 cores, 1 worker): 5.76 ms. Throughput: 173.55 iter/sec. Timings for 2880K FFT length (4 cores, 1 worker): 5.93 ms. Throughput: 168.57 iter/sec. Timings for 3072K FFT length (4 cores, 1 worker): 6.61 ms. Throughput: 151.36 iter/sec. Timings for 3200K FFT length (4 cores, 1 worker): 6.75 ms. Throughput: 148.04 iter/sec. Timings for 3360K FFT length (4 cores, 1 worker): 7.27 ms. Throughput: 137.64 iter/sec. Timings for 3456K FFT length (4 cores, 1 worker): 7.47 ms. Throughput: 133.79 iter/sec. Timings for 3584K FFT length (4 cores, 1 worker): 7.77 ms. Throughput: 128.73 iter/sec. Timings for 3840K FFT length (4 cores, 1 worker): 8.45 ms. Throughput: 118.30 iter/sec. Timings for 4096K FFT length (4 cores, 1 worker): 8.57 ms. Throughput: 116.64 iter/sec. Timings for 4480K FFT length (4 cores, 1 worker): 9.36 ms. Throughput: 106.81 iter/sec. Timings for 4608K FFT length (4 cores, 1 worker): 9.96 ms. Throughput: 100.41 iter/sec. Timings for 4800K FFT length (4 cores, 1 worker): 10.19 ms. Throughput: 98.12 iter/sec. Timings for 5120K FFT length (4 cores, 1 worker): 11.15 ms. Throughput: 89.69 iter/sec. Timings for 5376K FFT length (4 cores, 1 worker): 11.97 ms. Throughput: 83.53 iter/sec. Timings for 5760K FFT length (4 cores, 1 worker): 12.94 ms. Throughput: 77.29 iter/sec. Timings for 6144K FFT length (4 cores, 1 worker): 13.08 ms. Throughput: 76.46 iter/sec. Timings for 6400K FFT length (4 cores, 1 worker): 14.38 ms. Throughput: 69.54 iter/sec. Timings for 6720K FFT length (4 cores, 1 worker): 14.89 ms. Throughput: 67.18 iter/sec. Timings for 6912K FFT length (4 cores, 1 worker): 15.10 ms. Throughput: 66.21 iter/sec. Timings for 7168K FFT length (4 cores, 1 worker): 15.91 ms. Throughput: 62.86 iter/sec. Timings for 7680K FFT length (4 cores, 1 worker): 16.93 ms. Throughput: 59.07 iter/sec. Timings for 8064K FFT length (4 cores, 1 worker): 18.22 ms. Throughput: 54.87 iter/sec. Timings for 8192K FFT length (4 cores, 1 worker): 18.80 ms. Throughput: 53.20 iter/sec. [B]NEW i5 9600K @ stock 3.7Ghz with 32GB (16GBx2) of DDR4 3600Mhz:[/B] Timings for 2048K FFT length (4 cores, 1 worker): 2.07 ms. Throughput: 483.82 iter/sec. Timings for 2304K FFT length (4 cores, 1 worker): 2.30 ms. Throughput: 434.59 iter/sec. Timings for 2400K FFT length (4 cores, 1 worker): 2.43 ms. Throughput: 411.18 iter/sec. Timings for 2560K FFT length (4 cores, 1 worker): 2.67 ms. Throughput: 374.39 iter/sec. Timings for 2688K FFT length (4 cores, 1 worker): 2.79 ms. Throughput: 358.41 iter/sec. Timings for 2880K FFT length (4 cores, 1 worker): 3.02 ms. Throughput: 330.90 iter/sec. Timings for 3072K FFT length (4 cores, 1 worker): 3.26 ms. Throughput: 306.33 iter/sec. Timings for 3200K FFT length (4 cores, 1 worker): 3.37 ms. Throughput: 296.88 iter/sec. Timings for 3360K FFT length (4 cores, 1 worker): 3.68 ms. Throughput: 271.65 iter/sec. Timings for 3456K FFT length (4 cores, 1 worker): 3.71 ms. Throughput: 269.45 iter/sec. Timings for 3584K FFT length (4 cores, 1 worker): 3.84 ms. Throughput: 260.69 iter/sec. Timings for 3840K FFT length (4 cores, 1 worker): 4.17 ms. Throughput: 239.54 iter/sec. Timings for 4096K FFT length (4 cores, 1 worker): 4.45 ms. Throughput: 224.57 iter/sec. Timings for 4480K FFT length (4 cores, 1 worker): 4.87 ms. Throughput: 205.14 iter/sec. Timings for 4608K FFT length (4 cores, 1 worker): 4.96 ms. Throughput: 201.74 iter/sec. Timings for 4800K FFT length (4 cores, 1 worker): 5.33 ms. Throughput: 187.67 iter/sec. Timings for 5120K FFT length (4 cores, 1 worker): 5.64 ms. Throughput: 177.28 iter/sec. Timings for 5376K FFT length (4 cores, 1 worker): 5.99 ms. Throughput: 167.06 iter/sec. Timings for 5760K FFT length (4 cores, 1 worker): 6.45 ms. Throughput: 155.06 iter/sec. Timings for 6144K FFT length (4 cores, 1 worker): 6.86 ms. Throughput: 145.75 iter/sec. Timings for 6400K FFT length (4 cores, 1 worker): 7.20 ms. Throughput: 138.97 iter/sec. Timings for 6720K FFT length (4 cores, 1 worker): 7.60 ms. Throughput: 131.62 iter/sec. Timings for 6912K FFT length (4 cores, 1 worker): 7.97 ms. Throughput: 125.52 iter/sec. Timings for 7168K FFT length (4 cores, 1 worker): 8.16 ms. Throughput: 122.56 iter/sec. Timings for 7680K FFT length (4 cores, 1 worker): 8.68 ms. Throughput: 115.25 iter/sec. Timings for 8064K FFT length (4 cores, 1 worker): 9.27 ms. Throughput: 107.92 iter/sec. Timings for 8192K FFT length (4 cores, 1 worker): 9.51 ms. Throughput: 105.17 iter/sec. [B]NEW i7 9700K @ stock 3.6Ghz with 16GB (2x8GB) DDR4 4500Mhz (downclocked to 4360 Mhz for stability)[/B] Timings for 2048K FFT length (4 cores, 1 worker): 2.12 ms. Throughput: 472.02 iter/sec. Timings for 2304K FFT length (4 cores, 1 worker): 2.45 ms. Throughput: 408.10 iter/sec. Timings for 2400K FFT length (4 cores, 1 worker): 2.57 ms. Throughput: 388.40 iter/sec. Timings for 2560K FFT length (4 cores, 1 worker): 3.00 ms. Throughput: 333.33 iter/sec. Timings for 2688K FFT length (4 cores, 1 worker): 3.14 ms. Throughput: 318.78 iter/sec. Timings for 2880K FFT length (4 cores, 1 worker): 3.47 ms. Throughput: 288.44 iter/sec. Timings for 3072K FFT length (4 cores, 1 worker): 3.78 ms. Throughput: 264.21 iter/sec. Timings for 3200K FFT length (4 cores, 1 worker): 4.03 ms. Throughput: 248.41 iter/sec. Timings for 3360K FFT length (4 cores, 1 worker): 4.33 ms. Throughput: 230.71 iter/sec. Timings for 3456K FFT length (4 cores, 1 worker): 4.44 ms. Throughput: 225.21 iter/sec. Timings for 3584K FFT length (4 cores, 1 worker): 4.55 ms. Throughput: 219.63 iter/sec. Timings for 3840K FFT length (4 cores, 1 worker): 5.22 ms. Throughput: 191.70 iter/sec. Timings for 4096K FFT length (4 cores, 1 worker): 5.40 ms. Throughput: 185.13 iter/sec. Timings for 4480K FFT length (4 cores, 1 worker): 6.13 ms. Throughput: 163.15 iter/sec. Timings for 4608K FFT length (4 cores, 1 worker): 6.40 ms. Throughput: 156.16 iter/sec. Timings for 4800K FFT length (4 cores, 1 worker): 6.88 ms. Throughput: 145.42 iter/sec. Timings for 5120K FFT length (4 cores, 1 worker): 6.81 ms. Throughput: 146.79 iter/sec. Timings for 5376K FFT length (4 cores, 1 worker): 7.70 ms. Throughput: 129.84 iter/sec. Timings for 5760K FFT length (4 cores, 1 worker): 7.49 ms. Throughput: 133.53 iter/sec. Timings for 6144K FFT length (4 cores, 1 worker): 7.92 ms. Throughput: 126.26 iter/sec. Timings for 6400K FFT length (4 cores, 1 worker): 9.55 ms. Throughput: 104.75 iter/sec. Timings for 6720K FFT length (4 cores, 1 worker): 9.02 ms. Throughput: 110.83 iter/sec. Timings for 6912K FFT length (4 cores, 1 worker): 9.41 ms. Throughput: 106.26 iter/sec. Timings for 7168K FFT length (4 cores, 1 worker): 9.49 ms. Throughput: 105.43 iter/sec. Timings for 7680K FFT length (4 cores, 1 worker): 11.58 ms. Throughput: 86.34 iter/sec. Timings for 8064K FFT length (4 cores, 1 worker): 11.43 ms. Throughput: 87.51 iter/sec. Timings for 8192K FFT length (4 cores, 1 worker): 11.06 ms. Throughput: 90.43 iter/sec. It is interesting to me that the 9600K actually performs 1020% [U]faster[/U] than the 9700K, even though the RAM is actually 800Mhz slower. That 4500Mhz RAM was expensive, and I thought it would make everything faster. But it did not. Is the 9600K faster because it's using dual rank RAM (16GB sticks)? Or is it the 100Mhz slower processor? Or both? 
[QUOTE=simon389;499079]It is interesting to me that the 9600K actually performs 1020% [U]faster[/U] than the 9700K, even though the RAM is actually 800Mhz slower. That 4500Mhz RAM was expensive, and I thought it would make everything faster. But it did not. [b]Is the 9600K faster because it's using dual rank RAM (16GB sticks)?[/b] Or is it the 100Mhz slower processor? Or both?[/QUOTE]
Probably. Dual rank usually makes a 10% to 15% difference from what I've seen. When Prime95/mprime hits RAM, it hits it hard, faster than a single rank can operate. Useful numbers for future reference. Thanks! 
Try with CPUZ to make sure both are running dual channel RAM:
[url]https://www.cpuid.com/softwares/cpuz.html[/url] On the "Memory" tab there is a "Channel #" that should say "Dual". It seems weird to me that dual rank should be that much faster when the other RAM is higher clock rate, I read previously on the forum that dual rank only gave a few percent extra. Did you try 6 cores 1 worker on both? 
CPU Z says it is dual. And yes, I tested it with 6 cores.

For me your result is not surprise. Latency matter! I'm sure that 4500 ram has huge values for CL and so on ...
But try to downgrade your 4500 kit to 3600 but for smallest CL as you can run in stable. Interesting to see the difference in this case. 
Planning a build to perform LLR tests on numbers from 1.5m5m bits. With FFT's of this size (much smaller than world record sizes), would memory bandwidth be as much of a concern? Could FFT's of this size fit on L3 cache?
I've decided on using a hexacore i59600k with an msi mpg z390 motherboard which supports quad channel & up to 4400 mhz ram. I have 2 1060 6gb and a 980ti laying around and would like to connect them to the build as well for crypto mining (I don't pay electricity costs)/LLR testing/neural network training. What should I get? I was looking around at 4x 8gb 3600 mHz ram sticks for $180 total. Certainly pricey for RAM. Thoughts? Overkill for my processor? Or still too slow? 
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