i5-6400 vs 6600 (for prime hunting)
 

I've been learning that for LL testing, memory speed is king. Everything else equal (lets assume DDR4-3200 in both systems), do you expect the i5-6600 would perform even a little better (prime hunting) than the 6400? The 6600 is only about $30 more, but I figure why spend the money if the cpu isn't the bottleneck. Thoughts?

My impression is that quad-channel memory makes the most difference. Unfortunately, that limits you to high-end i7s, and [STRIKE]low-end[/STRIKE] some Xeons, I think.

Given your apparent price range, your reasoning is probably correct if the RAM is dual-channel. What is the speed bump between the 6400 and 6600?

[QUOTE=kladner;425502]My impression is that quad-channel memory makes the most difference. Unfortunately, that limits you to high-end i7s, and [STRIKE]low-end[/STRIKE] some Xeons, I think.

Given your apparent price range, your reasoning is probably correct if the RAM is dual-channel. What is the speed bump between the 6400 and 6600?[/QUOTE]

6400 is 2.7 GHz $184
6500 is 3.3 GHz + $16
6600 is 3.4 GHz + $16 more

For bang for the buck, I would get the 6500. You lose 3% speed, but save 7.4% on CPU cost. All three have the same thermal envelop, so none will save you running costs.

I would also consider DDR4-3000 as it's significantly cheaper than DDR-3200 if you are on a budget. It's a 9.4% drop in memory speed, but from the numbers I've seen around here, going from 3000 to 3200 doesn't result in close to a 9.4% increase in performance (more bandwidth doesn't mean that at a given moment the memory bus still isn't saturated serving requests; it only shortens the periods of saturation).

If you want to optimize for cost further, get a bare-bones non-overclocking motherboard for a lot cheaper and go with DDR-2133 and the 6500. The money you save can go towards buying more systems. Or spend the money and get an unlocked processor, overclock it, and squeeze as much as you can out of DDR-3200 memory and the rest of the components. Mixing the two ideas isn't as cost efficient.

I see the dollar sign bug rears its head again. Hopefully it is fixed soon.

[QUOTE=Mark Rose;425506]
If you want to optimize for cost further, get a bare-bones non-overclocking motherboard for a lot cheaper and go with DDR-2133 and the 6500. .[/QUOTE]

My analysis is the best bang for the buck system is the 6500 with DDR4-3000 (or better).

[QUOTE=Prime95;425508]My analysis is the best bang for the buck system is the 6500 with DDR4-3000 (or better).[/QUOTE]

I'm sure you've put more effort into the numbers than I have :)

[QUOTE=Mark Rose;425506]6400 is 2.7 GHz $184
6500 is 3.3 GHz + $16
6600 is 3.4 GHz + $16 more

For bang for the buck, I would get the 6500. You lose 3% speed, but save 7.4% on CPU cost. All three have the same thermal envelop, so none will save you running costs.[/QUOTE]
[URL]http://ark.intel.com/compare/88185,88184,88188[/URL]

2.7, 3.2 & 3.3 resp.

Definitely, 6500 and 6600 will give more performance. 2.7 Ghz isn't sufficient to fully bottleneck on memory.

OTOH, 2.7 should burn significantly less wattage (TDP is more of a system design guidance than actual wattage)

[QUOTE=kladner;425502]My impression is that quad-channel memory makes the most difference. Unfortunately, that limits you to high-end i7s, and [STRIKE]low-end[/STRIKE] some Xeons, I think.[/QUOTE]

These are all Skylake processors and none of those have quad channel memory. Not until Skylake Xeons and Skylake-E and probably not until 2017.

For quad channel right now you need Haswell-E/Xeon and soon Broadwell-E/Xeon but those are all 2 to 5+ times more expensive than this.

[QUOTE=axn;425510][url]http://ark.intel.com/compare/88185,88184,88188[/url]

2.7, 3.2 & 3.3 resp.

Definitely, 6500 and 6600 will give more performance. 2.7 Ghz isn't sufficient to fully bottleneck on memory.

OTOH, 2.7 should burn significantly less wattage (TDP is more of a system design guidance than actual wattage)[/QUOTE]

I misread the chart I was looking at. My bad. I read the numbers for the 6700 and 6600 for the 6600 and 6500.

It's interesting to note that the 6500's quad core turbo boost is significantly less than the other two's.

Here are benchmark results for i5-6500 with ddr4-2400 memory.

[QUOTE]Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz
CPU speed: 3098.61 MHz, 4 cores
CPU features: Prefetch, SSE, SSE2, SSE4, AVX, AVX2, FMA
L1 cache size: 32 KB
L2 cache size: 256 KB, L3 cache size: 6 MB
L1 cache line size: 64 bytes
L2 cache line size: 64 bytes
TLBS: 64
Prime95 64-bit version 28.7, RdtscTiming=1

Timings for 4096K FFT length (1 cpu, 1 worker): 15.57 ms. Throughput: 64.24 iter/sec.
Timings for 4096K FFT length (2 cpus, 2 workers): 16.48, 16.44 ms. Throughput: 121.48 iter/sec.
Timings for 4096K FFT length (3 cpus, 3 workers): 18.91, 18.77, 18.88 ms. Throughput: 159.14 iter/sec.
Timings for 4096K FFT length (4 cpus, 4 workers): 23.74, 23.56, 23.28, 23.15 ms. Throughput: 170.70 iter/sec.
[/QUOTE]

Very interesting to compare. Here's my results on a system with the i5-6600 and DDR4-2133.

Although quicker out of the gate with just one or two cores running, the memory bottleneck becomes blatantly clear. I think I'm going to put a 6500 in this system, and take the 6600 that's currently in it and put it in a new mobo that can handle faster ram.

[QUOTE]Intel(R) Core(TM) i5-6600 CPU @ 3.30GHz
CPU speed: 3379.17 MHz, 4 cores
CPU features: Prefetch, SSE, SSE2, SSE4, AVX, AVX2, FMA
L1 cache size: 32 KB
L2 cache size: 256 KB, L3 cache size: 6 MB
L1 cache line size: 64 bytes
L2 cache line size: 64 bytes
TLBS: 64
Prime95 64-bit version 28.7, RdtscTiming=1

Timings for 4096K FFT length (1 cpu, 1 worker): 14.24 ms. Throughput: 70.25 iter/sec. [COLOR="SeaGreen"]+6.01[/COLOR]
Timings for 4096K FFT length (2 cpus, 2 workers): 15.65, 15.60 ms. Throughput: 128.00 iter/sec. [COLOR="SeaGreen"]+6.52[/COLOR]
Timings for 4096K FFT length (3 cpus, 3 workers): 19.23, 19.87, 20.01 ms. Throughput: 152.30 iter/sec. [COLOR="Red"]-6.84[/COLOR]
Timings for 4096K FFT length (4 cpus, 4 workers): 24.37, 26.35, 26.51, 26.02 ms. Throughput: 155.12 iter/sec. [COLOR="Red"]-15.58[/COLOR][/QUOTE]