registered vs. unbuffered compatibility (P5BWD2)

  • Thread starter Thread starter David Madore
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David Madore

Hi,

This _must_ be a FAQ, yet I couldn't find the answer anywhere (or
rather, I found completely conflicting answers):

Will Registered ECC RAM work on a motherboard that calls for
"Unbuffered non-ECC / ECC RAM"?

(First, I'm not even sure how "Unbuffered non-ECC / ECC RAM" is to be
parsed: it could be "Unbuffered non-ECC" / "ECC" or "Unbuffered"
"ECC/non-ECC".)

Specifically, the RAM type would be DDR2-533 Registered ECC, and the
motherboard is a P5WD2.

Note that I am _not_ asking about mixing unbuffered and registered
RAM: I am aware that this will not work. I also understand that
registered RAM might loose a clock cycle for every memory access: this
is not a concern. I am merely asking whether the memory will work at
all (and as ECC).

Many FAQs explain the difference between registered and unbuffered
RAM, and between ECC and non-ECC, and imply that certain configs
require registered RAM (e.g., dual processor motherboards, any kind of
Opteron, etc.), but the point about certain motherboards requiring
_unbuffered_ RAM is not made. The motherboard's manual also makes no
particular warning (whereas it mentions a whole lot of things that
will _not_ work, such as trying to use DDR instead of DDR2). I am
also told that ECC RAM will work on non-ECC motherboards.

The reason for my concern is that it seems extremely difficult, if not
downright impossible, to get Unbuffered ECC RAM - let alone DDR2
Unbuffered ECC - here; in fact, one broker could not even be convinced
that it exists. It's most unfortunate having a motherboard that
supports a kind of memory that is impossible to find! On the other
hand, Registered ECC is relatively easy to find. (Also, it seems to
me that it would be massively stupid not to allow for the mere extra
clock cycle delay it takes to make Registered RAM usable on all
motherboards, but, well, stupidity is hardly ever a reason for things
being otherwise.)
 
David Madore wrote:

" Will Registered ECC RAM work on a motherboard that calls for
"Unbuffered non-ECC / ECC RAM"? "

No, it won't. You can get non-registered (unbuffered) ECC RAM, and it
is that which it refers to. Registed ECC RAM will not work if that is
how it's stated on the specs.
 
David Madore said:
Hi,

This _must_ be a FAQ, yet I couldn't find the answer anywhere (or
rather, I found completely conflicting answers):

Will Registered ECC RAM work on a motherboard that calls for
"Unbuffered non-ECC / ECC RAM"?

(First, I'm not even sure how "Unbuffered non-ECC / ECC RAM" is to be
parsed: it could be "Unbuffered non-ECC" / "ECC" or "Unbuffered"
"ECC/non-ECC".)

Specifically, the RAM type would be DDR2-533 Registered ECC, and the
motherboard is a P5WD2.

Note that I am _not_ asking about mixing unbuffered and registered
RAM: I am aware that this will not work. I also understand that
registered RAM might loose a clock cycle for every memory access: this
is not a concern. I am merely asking whether the memory will work at
all (and as ECC).

Many FAQs explain the difference between registered and unbuffered
RAM, and between ECC and non-ECC, and imply that certain configs
require registered RAM (e.g., dual processor motherboards, any kind of
Opteron, etc.), but the point about certain motherboards requiring
_unbuffered_ RAM is not made. The motherboard's manual also makes no
particular warning (whereas it mentions a whole lot of things that
will _not_ work, such as trying to use DDR instead of DDR2). I am
also told that ECC RAM will work on non-ECC motherboards.

The reason for my concern is that it seems extremely difficult, if not
downright impossible, to get Unbuffered ECC RAM - let alone DDR2
Unbuffered ECC - here; in fact, one broker could not even be convinced
that it exists. It's most unfortunate having a motherboard that
supports a kind of memory that is impossible to find! On the other
hand, Registered ECC is relatively easy to find. (Also, it seems to
me that it would be massively stupid not to allow for the mere extra
clock cycle delay it takes to make Registered RAM usable on all
motherboards, but, well, stupidity is hardly ever a reason for things
being otherwise.)
Click to expand...



David
If you need information on memory the best place to get it is here at the
OCZ forum:
http://www.bleedinedge.com/forum/forumdisplay.php?f=54
You will get answers from one of the tech support staff from OCZ.
Hope his helps,
Ken'
 
Buffered/registers vs unbuffered/unregistered and ECC vs nonECC are two
different issues. What I am about to post is very general and thus not
accurate, but it should do.

ECC just adds error correction capability to the module. In most cases
you can use ECC or non-ECC memory, you just WON'T get the benefit of ECC
unless you use all ECC memory in a ECC capable system with ECC enabled.
ECC memory just adds additional bits to the width of the 'word' of
memory being transferred - instead of a 'word' being 8/16/32 bits
10/18/36 bits are transferred - the calculation and checking of the
'parity' is done by the memory controller. Most nonECC systems just
don't know they are there.

I have seen some vendors specifically state that ECC capable memory is
not supported on their board. I haven't tested it, so I don't know if
there was a 'real' hardware compatibility issue or the vendor didn't
what the hassles of someone putting ECC memory in and magically
expecting it to work.

What is the downside of using non-ECC memory? You don't know if what
your getting from memory is what you put there. Is it a big thing?
Depends. For most of us: no, the likely hood of a bit being corrupted
is very small. The enabling of ECC does slow the system down a little -
there is overhead in calculating the checksum when storing or retrieving
each word of memory. ECC memory is also more expensive as there are
more chips on the module to support the ECC encoding.

Registered and buffered memory are the same thing. The memory module
has a buffer register between the memory chips and the memory
controller. Why? Basically it is a signal booster. The memory
contoller can only communicate with a limited number of chips - each
chip it communicates with requires a little current and the controller
has a limited amount of current it can generate. The use of the buffers
reduce the number of chips it has to talk to directly. So, with
unbuffered memory the controller might be able to talk to 3 DIMMs worth
of memory chips, with the use of buffers it might be able to talk to 24
DIMMs - the limit here is the number of chips it can communicate
directly with not the amount of memory it can address.

Your system specs should say whether you need registered memory or not.
If it doesn't state, then it probably wants unbuffered memory.

If you system only supports 1/2/3/4 slots, it probably uses unregistered
memory. If your system is a server supporting 5+ slots, it probably
uses registered. Some systems are capable of supporting either, but not
both at the same time, certain Opterons for example.

If you are having problems finding the right memory for you system, try
one of the online retailers. Here are two that have a presence in France
or the EU.

http://www.crucial.com/eu/
http://www.kingston.com/frroot/
 
Hi,

This _must_ be a FAQ, yet I couldn't find the answer anywhere (or
rather, I found completely conflicting answers):

Will Registered ECC RAM work on a motherboard that calls for
"Unbuffered non-ECC / ECC RAM"?
Click to expand...

Almost certainly not.
Many FAQs explain the difference between registered and unbuffered
RAM, and between ECC and non-ECC, and imply that certain configs
require registered RAM (e.g., dual processor motherboards, any kind of
Opteron, etc.), but the point about certain motherboards requiring
_unbuffered_ RAM is not made.
Click to expand...

As a general rule of thumb a motherboard either requires registered
memory or it requires unregistered memory. These days there are very
few boards that will work with either (older boards are a bit
different in this regard, but for new boards it usually one or the
other).
The motherboard's manual also makes no
particular warning (whereas it mentions a whole lot of things that
will _not_ work, such as trying to use DDR instead of DDR2).
Click to expand...

To put DDR memory in that board would require a hammer... don't do it!
I am
also told that ECC RAM will work on non-ECC motherboards.
Click to expand...

Generally speaking yes, though that's definitely not a sure-thing.
Usually if you put ECC memory in a board that doesn't support ECC it
will just ignore the extra chip and work exactly as if it was non-ECC
memory. However you are taking a bit of a chance doing so.
The reason for my concern is that it seems extremely difficult, if not
downright impossible, to get Unbuffered ECC RAM - let alone DDR2
Unbuffered ECC - here; in fact, one broker could not even be convinced
that it exists.
Click to expand...

It most definitely does exit. There's absolutely no requirement for
ECC memory to be registered/buffered. In fact, there's absolutely no
requirement for registered memory to be ECC, though non-ECC registered
memory is EXTREMELY rare.

Here's a link to some DDR2 667 ECC/unbuffered memory:

http://www.crucial.com/store/partspecs.Asp?IMODULE=CT6472AA667

Seems like this is what you were looking for? Crucial also carries
1GB parts as well as some DDR2 553 memory that should fit the bill.
It's most unfortunate having a motherboard that
supports a kind of memory that is impossible to find!
Click to expand...

Your motherboard does also support bog-standard non-registered,
non-ECC memory, so if ECC is not a requirement for your applications
you could go for that. If not, Crucial can definitely provide you
with memory that will work for you, though perhaps not with the
maximum speed DDR2 800. Kingston also has non-registered ECC memory,
as should most of the other bigger memory companies.
On the other
hand, Registered ECC is relatively easy to find. (Also, it seems to
me that it would be massively stupid not to allow for the mere extra
clock cycle delay it takes to make Registered RAM usable on all
motherboards, but, well, stupidity is hardly ever a reason for things
being otherwise.)
Click to expand...

There's more to it than just an extra clock cycle. It's rather tricky
(read: extra cost) to make a board that support BOTH registered and
non-registered memory these days. As such you're pretty much left
with one or the other.
 
Tony Hill in litteris said:
Almost certainly not.
Click to expand...

Thanks, and thanks to all others who answered.
To put DDR memory in that board would require a hammer... don't do it!
Click to expand...

That's my point: if you're going to bother stating that the user
shouldn't do something so obviously wrong as using a hammer to insert
the memory modules, why the hell don't they mention something much
subtly wrong, which is likely to confuse everyone, such as using
registered memory instead of unbuffered? At least on a motherboard
that will take ECC memory, which is *likely* to be found in
"registered" version even if it also exists as "unbuffered".

I mean, if nearly every motherboard either requires the one or
requires the other, why don't they notch them differently?
Here's a link to some DDR2 667 ECC/unbuffered memory:

http://www.crucial.com/store/partspecs.Asp?IMODULE=CT6472AA667

Seems like this is what you were looking for? Crucial also carries
1GB parts as well as some DDR2 553 memory that should fit the bill.
Click to expand...

Thanks for the link. In the meantime, my broker told me he could get
the right chips for me (here in France - or at least in Paris - we
usually go downtown to shop for computer parts rather than buying them
online). But I'll order online if there's a problem with that line.
Your motherboard does also support bog-standard non-registered,
non-ECC memory, so if ECC is not a requirement for your applications
you could go for that.
Click to expand...

Oh, definitely, in fact, that's the setup I'm using now (temporarily I
hope!), but I bought this motherboard for the sole reason that it
supports ECC memory (only a precious few of them do) so it would be a
shame if I couldn't have ECC memory at all.

I became completely paranoid on the question of using ECC memory after
I had to essentially throw away dozens of gigabytes of data, which I
had just moved from one hard drive to another, because of one goddamn
deffective bit. And now that I started being cautious I noticed that
the number of computers with at least one defective bit is dangerously
high.
There's more to it than just an extra clock cycle. It's rather tricky
(read: extra cost) to make a board that support BOTH registered and
non-registered memory these days. As such you're pretty much left
with one or the other.
Click to expand...

Out of curiosity, do you know where I could find some information as
to why it's more than just a timing issue?
 
That's my point: if you're going to bother stating that the user
shouldn't do something so obviously wrong as using a hammer to insert
the memory modules, why the hell don't they mention something much
subtly wrong, which is likely to confuse everyone, such as using
registered memory instead of unbuffered? At least on a motherboard
that will take ECC memory, which is *likely* to be found in
"registered" version even if it also exists as "unbuffered".

I mean, if nearly every motherboard either requires the one or
requires the other, why don't they notch them differently?
Click to expand...

I think it's because, at least in theory, you can still make a board
that supports both registered and non-registered memory in the same
slots. It just tends to be too tricky/expensive to do so for most
boards.

I wouldn't be too surprised if the next generation of memory does end
up having different notches of registered memory vs. non-registered.
Of course, the next generation of memory is likely to change the whole
idea of registered memory with FB-DIMMs anyway, so the point will
probably be moot.
Oh, definitely, in fact, that's the setup I'm using now (temporarily I
hope!), but I bought this motherboard for the sole reason that it
supports ECC memory (only a precious few of them do) so it would be a
shame if I couldn't have ECC memory at all.
Click to expand...

For Intel-based systems ECC support is pretty rare. Intel has decided
that only their top-end desktop chipsets can be graced with ECC
support. I would have thought that this might change given that
virtually ALL AMD systems now support ECC thanks to the integrated
memory controller on AMD's Athlon64 and even Sempron (not counting
Socket A Sempron) chips. Perhaps the next generation of Intel
chipsets will make ECC support more widely available.
I became completely paranoid on the question of using ECC memory after
I had to essentially throw away dozens of gigabytes of data, which I
had just moved from one hard drive to another, because of one goddamn
deffective bit. And now that I started being cautious I noticed that
the number of computers with at least one defective bit is dangerously
high.
Click to expand...

Yup, there have been many studies done on this over the past while,
and as memory sizes increases it's quickly becoming a more serious
issue. For most of us who are just playing around on home computers
its not a big worry, but for anyone that's serious about their data,
ECC is high recommended IMO.
Out of curiosity, do you know where I could find some information as
to why it's more than just a timing issue?
Click to expand...

I don't know off-hand, though you could probably find some info on
Intel's website if you search enough, Intel has rather extensive
technical documentation on all their products. Otherwise you might
want to see if Google turns up anything.
 
Tony Hill said:
I think it's because, at least in theory, you can still make a board
that supports both registered and non-registered memory in the same
slots. It just tends to be too tricky/expensive to do so for most
boards.
Click to expand...


It was much more common way back in the Pentium II days; both dual-Slot-1
systems I've owned have taken either registered or unregistered memory - you
just couldn't mix 'em at the same time, and my understanding is that that
was pretty standard.
 
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