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Memory and the Ryzen 3000



 
 
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  #1  
Old July 20th 19, 08:41 PM posted to alt.comp.hardware.pc-homebuilt
John Savard
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Posts: 1
Default Memory and the Ryzen 3000

I'm planning to put together a new computer using one of the new Ryzen processors.

I heard that 3600 MHz memory would provide the best performance for it, because
using faster memory would require something to be slowed down to two memory
cycles instead of one. Then I learned some more details: the Infinity Fabric
interconnect within the CPU runs at half the memory speed, to a maximum of 1800
MHz. So the faster memory even makes the chip work faster internally.

However, when looking for a motherboard, some were billed as supporting memory
up to 2666 MHz, and others as supporting memory up to 3200 MHz. But when I
looked at the *detailed* specs for the latter boards, they _did_ support
DDR4-3600 memory... as long as you were overclocking.

What?

If the memory's rated speed is 3600, how is running it at 3600 overclocking? Is
this some multiplier thing, the chip can't get its Infinity Fabric up to 1800 if
it stays at its rated clock speed?

Or is this just a garble, with the truth not as bad as it sounds: to use the
memory at its full rated speed, you will just have to go into the same BIOS
screen that people use if they're overclocking, but you don't have to actually
overclock anything.

Then I found that by buying two 8 GB sticks for my build, I had dodged another
bullet!

Had I gotten 32 GB of RAM on two 16 GB sticks instead, one web site told me I'd
never be able to use it at its rated speed - and I ran a good chance of the
computer not booting at all!

However, further searching turned up that this was an issue with the first-gen
Ryzen, and it got fixed by a BIOS update. Basically, Ryzens didn't like dual-
ranked memory, and 16 GB memory sticks are almost always dual-ranked, and 8 GB
memory sticks now are almost always single-ranked.

Still, apparently there is some risk in dual-ranked memory with Ryzen. I did
note that some memory was advertised as compatible with Ryzen, or as compatible
with Intel, so I chose, from what was available, something that didn't say it
was only for Intel, and which seemed to be on one site's list of memory that did
work with Ryzen.

In any case, it certainly seems like getting memory for a Ryzen system is a
complicated process.

John Savard
  #2  
Old July 20th 19, 10:46 PM posted to alt.comp.hardware.pc-homebuilt
Paul[_28_]
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Posts: 1,118
Default Memory and the Ryzen 3000

John Savard wrote:
I'm planning to put together a new computer using one of the new Ryzen processors.

I heard that 3600 MHz memory would provide the best performance for it, because
using faster memory would require something to be slowed down to two memory
cycles instead of one. Then I learned some more details: the Infinity Fabric
interconnect within the CPU runs at half the memory speed, to a maximum of 1800
MHz. So the faster memory even makes the chip work faster internally.

However, when looking for a motherboard, some were billed as supporting memory
up to 2666 MHz, and others as supporting memory up to 3200 MHz. But when I
looked at the *detailed* specs for the latter boards, they _did_ support
DDR4-3600 memory... as long as you were overclocking.

What?

If the memory's rated speed is 3600, how is running it at 3600 overclocking? Is
this some multiplier thing, the chip can't get its Infinity Fabric up to 1800 if
it stays at its rated clock speed?

Or is this just a garble, with the truth not as bad as it sounds: to use the
memory at its full rated speed, you will just have to go into the same BIOS
screen that people use if they're overclocking, but you don't have to actually
overclock anything.

Then I found that by buying two 8 GB sticks for my build, I had dodged another
bullet!

Had I gotten 32 GB of RAM on two 16 GB sticks instead, one web site told me I'd
never be able to use it at its rated speed - and I ran a good chance of the
computer not booting at all!

However, further searching turned up that this was an issue with the first-gen
Ryzen, and it got fixed by a BIOS update. Basically, Ryzens didn't like dual-
ranked memory, and 16 GB memory sticks are almost always dual-ranked, and 8 GB
memory sticks now are almost always single-ranked.

Still, apparently there is some risk in dual-ranked memory with Ryzen. I did
note that some memory was advertised as compatible with Ryzen, or as compatible
with Intel, so I chose, from what was available, something that didn't say it
was only for Intel, and which seemed to be on one site's list of memory that did
work with Ryzen.

In any case, it certainly seems like getting memory for a Ryzen system is a
complicated process.

John Savard


This kind of garble is a motherboard tradition :-/

The info here claims there is some leverage available in the settings.

https://www.tomshardware.com/reviews...view,6214.html

One setting that varies between 1..2 is "Command Rate". It's
the length of time the address and any strobes are place on the
command bus. Using two cycles extends the setup time to the second
cycle. Because UDIMMs heavily load the address bus, there is more
capacitance to drive on the command bus, than the data bus. Using
the two cycle setting means a higher clock can be used. With the
clock speeds used by modern memories, I don't see how you could
run Command Rate 1 any more, even with single rank memory.

Using Command Rate of 2, cuts the command bandwidth in half.
But when a memory transaction takes 50 or 100 cycles at
some god-awful high speed, who really cares at that point ?

And with the new split into chiplets, there is an electrical
noise benefit. AMD will have more freedom when picking
current drive levels for the memory buses. It would appear
in the past, they were using low drive (4mA in a 50 ohm environment,
instead of a closer match like 8mA). With the multitude of
silicon dice, there is more opportunity for splitting power
and noise, for doing a different VCore regulator setup and
so on. As to exactly how they do that, I haven't seen a mention
whether the whole thing runs off one monolithic VCore or not.

Anyway, enjoy your new toy. Two sticks of single or dual
rank would be a good start. Putting four sticks in, with
your emphasis on speed, wouldn't be a good idea. I would not
want to disappoint you, with an extended tuning exercise,
to make four work at full speed. But setting up
two sticks should take you about 30 seconds :-)
That was my experience the last time I got to
turn on XMP. Check the manual and make sure such
a convenience setting exists on your board. When I
filled the Test Machine with RAM, configuring that
was a bitch. No, it doesn't run at rated speed ...
But, on the other hand, I've never seen side effects
of a memory error on the Test Machine either.

Each generation has a certain mythology about setup,
and part of the fun of owning a new motherboard, is
picking a popular one, then finding a site like
ExtremeSystems and someone who knows what they're doing.
At some point, they can assemble a recipe for the
best tuning method (i.e. if you go off-track
and run the memory 40% faster than you're supposed to).
But getting a 3600 rated stick to run at 3600,
might be as simple as using XMP. Crack the manual
for the new motherboard, and see what they recommend.

The CPU has a recommended interface speed at stock.
The memory (as specified by JEDEC) has a rated speed,
but independent DIMM makers bin the chips and select
ones that are capable of running faster than stock.
The multitude of clock islands inside the IMC/CPU/membus
conspire to quantize ranges of clock rates (in some
cases requiring a core clock change or some other
setting, to get the best latency). The Tomshardware
article hints at this, in a general way.

Paul
  #3  
Old July 21st 19, 01:04 AM posted to alt.comp.hardware.pc-homebuilt
Flasherly[_2_]
external usenet poster
 
Posts: 2,265
Default Memory and the Ryzen 3000

On Sat, 20 Jul 2019 12:41:22 -0700 (PDT), John Savard
wrote:

In any case, it certainly seems like getting memory for a Ryzen system is a
complicated process.


Not to ignore existing builds, if you should be lucky to find your
component part selections, MB & MEM, within some reviews. I find
myself approaching My Motherboard selection for what that is, a MB
brand and type, for less of an initial decision permitted outside
influences. In a sense the MB is everything. I may also start in on
the socket support PDF, running through CPU iterations available from
a pulled- and used-sourced aftermarket, before ever getting around
considering memory.

Unlike memory, though, that I do then select for it, I'll pull and
list from available user reviews, to cross-reference it, to their
stated experience as satisfactory. New memory, then it is;- I like
placing all together, in an order, in case of an issue or (a highly
unlikely) sum-total dissatisfied return. Unfortunately, used CPUs off
a side market will not fit into that scenario and are a liability.

Anyway, memory speeds and overclocking come secondary to overall
stability, and that is, likely, at some unstated vantage for price -
personally, I usually don't spend much or generally need a lot of
physical memory for the applications I'm often on.

Thus, the path of least resistance then goes to prove I'm such a Dull
Boy if I haven't actually any stringent demands.
 




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