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*** AMD "Zen 4" thread (inc AM5/APU discussion) ***

Infinity fabric clockspeed news:

https://www.hardwaretimes.com/ddr5-...seemingly-the-sweet-spot-for-ryzen-7000-cpus/

Running the IF clock at 2000mhz helps to reduce latency between the CPU and DDR5 memory:

Fc55jKmacAAKP-0-1536x864.png.webp


Another 166mhz further reduces latency by 0.8ns. Based on that, it looks like it might be possible to reduce latency by a further ~4.8ns, if the IF clock could be increased to 2996mhz-3000mhz.
 
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I think most chips will be limited to an IF clock of approx. 2000mhz (according to AMD, it's best set to Auto). I think AMD managed ~63 with decent DDR5 modules, so I've got no idea if latencies <60 will be possible on Zen 4. The reason for the small increase in latency, is apparently down to cache changes "The expansion of the L2 cache increased latency somewhat, from 12 to 14. The shared L3 cache's latency has also increased, from 46 to 50 cycles".

Hopefully, 60ns will be achievable, which was a typical latency for the 5900X and 5950X.
 
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g67575 said:
I think most chips will be limited to an IF clock of approx. 2000mhz (according to AMD, it's best set to Auto). I think AMD managed ~63 with decent DDR5 modules, so I've got no idea if latencies <60 will be possible on Zen 4. The reason for the small increase in latency, is apparently down to cache changes "The expansion of the L2 cache increased latency somewhat, from 12 to 14. The shared L3 cache's latency has also increased, from 46 to 50 cycles".

Hopefully, 60ns will be achievable, which was a typical latency for the 5900X and 5950X.
Click to expand...

I got 61.7 on junk RAM overclocked.

GsO5X1G.png
 
I think as long as the latency is roughly the same as Zen 3, that will be fine. The latency does seem to be a bit lower for the 5900X and 5950X, compared to the 5800X and 5600X.

It would be interesting to see what would happen if it were possible to run Zen 3/Zen 4 at 100ns or more, maybe by forcing higher RAM timings and lower frequencies in the BIOS. I would guess that the main difference, might be lower minimum framerates in games.
 
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If 63ns is on AMDs velocity ram or whatever it's called then I wonder what the latency will look like on the HW unboxed recommended budget 4800/40 stuff.
 
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