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Old 2019-12-26, 19:33   #45
scan80269
 
"Sam"
Jun 2019
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Z390 motherboards all support dual channel memory, not quad channel. Most ATX form factor motherboards feature 4 DIMM sockets, thus 2 DIMMs per memory channel.

Options for true quad channel memory:
- Intel X99 motherboard supporting Intel Haswell-E / Broadwell-E Core X series CPUs
- Intel X299 motherboard supporting Intel Skylake-X / Cascade Lake-X Core X series CPUs
- AMD X399 motherboard supporting AMD TR4 socket Ryen Threadripper X series CPUs
- AMD TRX40 motherboard supporting AMD 3rd gen Ryzen Threadripper series CPUs

Other motherboards featuring Intel Z390, Z370, etc. and AMD X570, X470 etc. are all dual-channel designs.

My two fastest systems for LL/PRP are both X99 with i7-5960X Haswell-E 8-core CPUs and quad channel DDR4 dual-rank memory configurations, at 3000MHz CL15 and 2133MHz CL13 respectively (the second X99 board lacks XMP support so cannot run DDR4 memory above 2133). Several other systems based on Z390 / Coffee Lake 6/8-core CPUs and Z270 / Kaby Lake 4-core CPUs with dual-channel DDR4 memory are all significantly slower.
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Old 2019-12-26, 21:17   #46
Trilo
 
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"W. Byerly"
Aug 2013
1423*2^2179023-1

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Quote:
Originally Posted by scan80269 View Post
Z390 motherboards all support dual channel memory, not quad channel. Most ATX form factor motherboards feature 4 DIMM sockets, thus 2 DIMMs per memory channel.

Options for true quad channel memory:
- Intel X99 motherboard supporting Intel Haswell-E / Broadwell-E Core X series CPUs
- Intel X299 motherboard supporting Intel Skylake-X / Cascade Lake-X Core X series CPUs
- AMD X399 motherboard supporting AMD TR4 socket Ryen Threadripper X series CPUs
- AMD TRX40 motherboard supporting AMD 3rd gen Ryzen Threadripper series CPUs

Other motherboards featuring Intel Z390, Z370, etc. and AMD X570, X470 etc. are all dual-channel designs.

My two fastest systems for LL/PRP are both X99 with i7-5960X Haswell-E 8-core CPUs and quad channel DDR4 dual-rank memory configurations, at 3000MHz CL15 and 2133MHz CL13 respectively (the second X99 board lacks XMP support so cannot run DDR4 memory above 2133). Several other systems based on Z390 / Coffee Lake 6/8-core CPUs and Z270 / Kaby Lake 4-core CPUs with dual-channel DDR4 memory are all significantly slower.
Thank you for the clarification I'm new to building PC's and assumed #of DIMM sockets= #of channels.

My original basis for choosing the i5 9600k is the high gflops/core scoring based on primegrid and gimps benchmarks.

https://www.primegrid.com/cpu_list.php

As for the 9600k build suppose I only fill 2 DIMMs with ram thus saving about $80. Would this have a non-negligable drop in speed vs. filling all 4 DIMMs with ram. Both would be dual channel regardless.

Would memory still be a hurdle for LLR tests of numbers between 1.5-5m bits? This is an order of magnitude smaller than numbered used in LL tests. The 9600k has 9MiB of L3 cache. Could the FFT's of smaller candidates be stored in there? If so then perhaps the bottleneck for candidates of these sizes would once again be CPU speed. Or is it too small for FFT's of those sizes?

Last fiddled with by Trilo on 2019-12-26 at 21:19
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Old 2019-12-27, 05:53   #47
VBCurtis
 
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"Curtis"
Feb 2005
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I run LLR on exponents from 3M to 7M on Haswell-era quad-core dual-channel machines, and I do run into memory saturation on the 4th test. That is, 3 copies of LLR running is nearly as fast as 4, when all run single-threaded. That's with an office-machine-grade Dell, with stock DDR4 at stock speed (2133?). If you run 3200 memory, you're getting 50% more bandwidth, and it's possible that running each test 2- or 3- threaded will not saturate the memory (that is, enough data will stay in cache).
Without relying on cache to save you, I'd think 3600 memory and that 6-core would match up well for tests around 3-5mbits each. As your tests grow in the future, you can go more multithreaded.
Hopefully, someone with more recent/similar hardware can amplify my hand-waving about bandwidth...
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