Full Buffer Support?

[latot]

Hi hi, I'm trying to understand the support for Full Buffer in ram, I understand for what it is, like ECC, but....

 

I was reading the motherboard ASUS ROG Crosshair VIII Dark Hero tech descriptions, and I noted this:

 

AMD Ryzen^TM 3000 G-Series / 2000 G-Series Processors

4 x DIMM, Max. 128GB, DDR4 3200(O.C.)/3000(O.C.)/2933/2800/2666/2400/2133 MHz Non-ECC, Un-buffered Memory

AMD Ryzen™ 5000 Series/ 3000 Series Desktop Processors

Dual Channel Memory Architecture

ECC Memory (ECC mode) support varies by CPU.

 

Well, in the 3000 series we know the motherboard does not support ECC and buffered memoery, buttt..., in the 5000 series we get support for ECC, but does not tell us if support buffered memory.

 

For ECC memory the CPU need t support it, and (I suppose) the motherboard, but maybe I'm wrong? While the CPU support ECC the motherboard will support it?

 

And what happenns with buffered memory? is the same a "Buffered Memory" and a "Full Buffer Memory"?, maybe there can be a buffered memory that is not ECC, how can I know a system support it?

 

I'm not trying to know if this motherboard support it or not, I wan't to know how to detect the support of Full Buffer memory.

 

Thx!

[mariushm]

no.

 

AM4 and AM5 support only UNBUFFERED / UNREGISTERED  DDR4 / DDR5  with ECC optional.  am4= only ddr4 , am5 = only ddr5

 

ECC means sticks have an extra ram chip which holds error correction info. The AMD processors support it, but it's up to motherboard maker to enable support for it.

 

Registered or FB (Fully Buffered) sticks are for servers or high end stuff (latest Threadripper chips), won't work with Ryzen chips

 

[latot]

Mmmm, this depends more on the Socket or de CPU it self?

 

And, continue with Full Buffer, it need to be supported by the CPU and the motherboard? and how can I know that? lets pick as example the motherboard above, where can I see does not support FB?

 

Thx!

[mariushm]

It depends on the memory controller which happens to be located inside the CPU. To a lesser degree, it depends on the cpu socket as well.

 

I don't think there's a pinout difference between unbuffered/buffered sticks but I cant say that with 100% certainty, Assuming this is correct, supporting fully buffered ram sticks wouldn't need another socket with more pins/contacts.

 

Fully buffered RAM sticks have an extra chip (which processes signals, not just a plain memory chip like in the case of ECC) which buffers requests to/from ram chips on the ram stick, so that makes them different from regular unbuffered memory sticks, and makes the memory controller more complex.

There's also Load Reduced RAM sticks, which also use a chip between the memory controller and the actual memory sticks

 

Quoting from Wikipedia

 

Quote

In addition to bandwidth and capacity variants, DDR4 modules can optionally implement:

• ECC, which is an extra data byte lane used for correcting minor errors and detecting major errors for better reliability. Modules with ECC are identified by an additional ECC in their designation. PC4-19200 ECC or PC4-19200E is a PC4-19200 module with ECC.^[52]
• Be "registered" ("buffered"), which improves signal integrity (and hence potentially clock rates and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, e.g. PC4-19200R. Typically modules with this designation are actually ECC Registered, but the 'E' of 'ECC' is not always shown. Whereas non-registered (a.k.a. unbuffered RAM) may be identified by an additional U in the designation. e.g. PC4-19200U.^[52]
• Be Load reduced modules, which are designated by LR and are similar to registered/buffered memory, in a way that LRDIMM modules buffer both control and data lines while retaining the parallel nature of all signals. As such, LRDIMM memory provides larger overall maximum memory capacities, while addressing some of the performance and power consumption issues of FB memory induced by the required conversion between serial and parallel signal forms.^[52]

 

For ECC sticks the difference between non-ECC and ECC sticks is literally an extra identical chip as the other chips on the ram stick .. for every 8 chips, there's a 9th ram chip of same size, and the memory controller uses it to store parity (error checking and correction information)

The DDR slot is designed from the start with the contacts for this 9th memory chip and majority of manufacturers will put traces from those contacts to the contacts/pins in the cpu socket, because there's practically no benefit to not do it - it's not like you can use those millimeters of space on the motherboard for anything else.

The memory controller will use the memory chip if detected on the sticks, and if the BIOS sends the commands to enable the usage of this memory chip.

Intel artificially locks ECC so that it's only working on server chips, AMD doesn't restrict it, but officially supports it only on their "Pro" labeled processors.  They don't guarantee ECC will work if you use ECC sticks, but it will simply use those sticks as sticks without ECC, if the motherboard doesn't handle the ECC part.

 

[latot]

Great!, when you mean, the support for FB in socket, you means the support only depends in the sockt it self? the motherboard does not need anything extra?, while the CPU support it we can use FB/no FB rams?

[mariushm]

NO, you misunderstand, or maybe I don't explain it properly..  Generally, a CPU socket is designed to support only some things, and therefore processors in turn will only support some things. When a processor adds something new for which there aren't pins in the socket, they change the socket. 

So for example AM4 is designed to support only DDR4 and there's no contacts or pins extra to support DDR5 memory sticks, and either way there's no will to add DDR5 support because you would just cause confusion - people would buy DDR5 and a DDR4 only motherboard and complain and do refunds, RMAs etc

Intel's 12gen processors were designed to support both DDR5 and DDR5 because at launch DDR5 was still expensive, so they put the pins in socket and now you can buy motherboards with either DDR4 or DDR5 but not both at same time.

AMD's AM5 supports only DDR5...

 

The processor only supports  specific types of memory sticks.

 

Ex 

Ryzen processors without Pro in name support Unbuffered DDR4  with or without ECC option. Nothing else. 

Ryzen processors with Pro in name support Unbuffered DDR4 with or without ECC but ECC is officially "supported" by AMD and as the "Pro" processors are sold to OEM manufacturers only, that's supposed to guarantee motherboard is properly made and enables ECC in bios and supports it properly.

Threadripper 1st generation supported only Unbuffered DDR4 with or without ECC,  2nd generation increased the maximum capacity possible from 256 GB to 2 TB, and 3rd generation (on a different CPU socket) also supports Registered and Load Reduced DDR4, and 3DS Registered DDR4 which are different than Unbuffered DDR4

 

You look at what the processor supports and those are the sticks that the motherboard supports. Sticks with extra stuff won't work.