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Memory confusion or confused about memory.



 
 
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  #1  
Old October 23rd 03, 02:09 AM
Spam Me Please
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Posts: n/a
Default Memory confusion or confused about memory.

Hi,

I'm looking at memory for the opteron, and ran across this at one
vendors web site.

ECC+registered memory
Registered memory only

What is the difference? I thought that all Registered memory was ECC.

Could be the vendors web site is wrong or I don't really understand
what is registered memory. Did some searching on google but nothing
came up to clear the matter.

Thanks for any info.

Alan
  #2  
Old October 23rd 03, 02:23 AM
Spam Me Please
external usenet poster
 
Posts: n/a
Default

Well some more searching and found the answer. Really adding some good
key words. I was getting tons of memory for sale at first.

What is meant by Registered memory?

"Registered" is a means of "Buffering" the memory in SDRAM. This means
that the clock signal is boosted across the entire array of memory
chips so that the computer sees a clean sharp clock signal instead of
a weakening clock signal as it progresses along the length of the
memory path. Registered memory must be supported by the system board
and cannot be mixed with "Unbuffered" modules.

You must have only Registered memory to use Registered memory. This is
a further means of eliminating the possibility of errors when reading
the data in memory and is used when the data returned from memory is
extremely critical, such as in scientific or financial calculations
where the integrity of the data is CRITICAL. It also allows a module
to be built using more chips, allowing for larger capacity modules to
be made.

************************************************** *

Therefore I see that registered is different from ECC+registered.
Anyway why do the opteron/athlon64 boards require registered and/or
ECC+registered memory?

Thanks

"Spam" == Spam Me Please writes:


Spam Hi, I'm looking at memory for the opteron, and ran across this
Spam at one vendors web site.

Spam ECC+registered memory Registered memory only

Spam What is the difference? I thought that all Registered memory
Spam was ECC.

Spam Could be the vendors web site is wrong or I don't really
Spam understand what is registered memory. Did some searching on
Spam google but nothing came up to clear the matter.

Spam Thanks for any info.

Spam Alan
  #3  
Old October 23rd 03, 02:46 PM
Yousuf Khan
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Posts: n/a
Default

"Spam Me Please" wrote in message
...
Therefore I see that registered is different from ECC+registered.
Anyway why do the opteron/athlon64 boards require registered and/or
ECC+registered memory?


Actually, it's only the Opteron and Athlon 64FX that requires it, but not
the regular Athlon 64. The reason the Opt/A64FX require registered memory is
because they are the same chip, an A64FX is just a renamed Opteron
100-series. Since the Opterons are server chips, they need to be able hold a
lot of memory modules, so it needs to be registered memory. If it weren't
registered then these processors couldn't hold much more than two or three
memory modules before their signal got all wonky.

Why ECC memory? For the same reason as why registered memory, these chips
have their background in server systems, where reliability is most
important.

Yousuf Khan


  #4  
Old October 23rd 03, 10:49 PM
Spam Me Please
external usenet poster
 
Posts: n/a
Default


Thanks for the information. Actually a better explanation than what I
found on google. Interesting the Athlon 64 can use either ECC or
Non-ECC unbuffered memory. At the least the boards that I have looked
at.

I guess it does not make much difference for a small office server.

Thanks

"Yousuf" == Yousuf Khan writes:


Yousuf "Spam Me Please" wrote in message
Yousuf ...
Therefore I see that registered is different from ECC+registered.
Anyway why do the opteron/athlon64 boards require registered
and/or ECC+registered memory?


Yousuf Actually, it's only the Opteron and Athlon 64FX that requires
Yousuf it, but not the regular Athlon 64. The reason the Opt/A64FX
Yousuf require registered memory is because they are the same chip,
Yousuf an A64FX is just a renamed Opteron 100-series. Since the
Yousuf Opterons are server chips, they need to be able hold a lot of
Yousuf memory modules, so it needs to be registered memory. If it
Yousuf weren't registered then these processors couldn't hold much
Yousuf more than two or three memory modules before their signal got
Yousuf all wonky.

Yousuf Why ECC memory? For the same reason as why registered memory,
Yousuf these chips have their background in server systems, where
Yousuf reliability is most important.

Yousuf Yousuf Khan


  #5  
Old October 24th 03, 01:29 AM
Tony Hill
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Default

On Wed, 22 Oct 2003 20:23:06 -0500, Spam Me Please
wrote:
snip
Therefore I see that registered is different from ECC+registered.


Yup. It is possible to get non-ECC registered memory, but that stuff
is REALLY rare. Besides which ECC is a GOOD thing to have, so just
stick with the registered ECC memory.

Anyway why do the opteron/athlon64 boards require registered and/or
ECC+registered memory?


Athlon64 does not require registered memory, the Opteron and the
Athlon64 FX do. The reason has to do with a combination of the target
market and expected memory configuration of the Opteron vs. the
Athlon64.

The first thing to point is the reason why you would use registered
memory. SDRAM and DDR SDRAM use a memory bus, so all chips on the bus
are connected together. In your typical memory module you have 8 or
16 memory chips. Now put 3 or 4 memory modules on the same bus and
you can easily get up around 50+ chips on the same bus. Each one of
these chips requires a little bit of current for it's clock, and if
you start getting up beyond about 32 chips on the bus, it quickly
becomes impossible to provide that much current. What's worse, the
more current draw you have, the "dirtier" your signal becomes, leading
to potential memory errors (= BAD!). As memory speeds have become
higher, this has become harder and harder to deal with.

So, rather than doing this, you use registered memory. So now,
instead of sending the signals to each individual memory chip, you
send them to a single buffer chip on the module. So, with 4 modules
on your memory bus, you now have only 4 chips to send signals to
instead of 50+ chips.

Obviously if you only have a single module or even two modules on the
bus, registered memory isn't really needed, but if you're going to put
a lot of memory in the system, it quickly becomes a requirement.

So, that brings up back to the target market. Opteron is targeted at
the server and high-end workstation market, where lots of memory is
common. Ideally the Opteron might have been designed where you could
put only two unregistered modules in the system or use registered
modules if you wanted more memory, but this may not have been an
option. As such, AMD made the trade-off to allow more memory (good
thing) but required registered memory. Similarly most Intel Xeon
motherboards require registered memory.

With the Athlon64 you are looking at a desktop processor, designed for
relatively small amounts of memory. As such, AMD designed it to use
the cheaper unregistered memory.

The Athlon64 FX is a bit of an odd-ball here. This chip is actually
just an Opteron processor that is being rebadged and marketed as a
desktop processor. Nothing really wrong with this, but as an Opteron
chip, it requires registered memory for the time being. It is
expected that AMD will change the design of the Athlon64 FX to allow
for unregistered memory in the relatively near (next 6 months?)
future. In doing so though, the new Athlon64 FX chips (currently
referred to as "Socket 939" models, due to the new socket they are
expected to use) will not be compatible with current boards.


A quick note about ECC. With Intel's i865 and i875 chipsets, as well
as AMD's new Athlon64 and Opteron chips, ECC is supported by most
systems these days (unfortunately most AthlonXP motherboards do not
support it). ECC is a GOOD THING! It will detect and correct soft
memory errors. With new systems coming with more and more memory,
soft memory errors are becoming more common. According to a rather
extensive study by IBM, with 256MB of memory you can expect 1 soft
memory per month. With 512MB of memory, as is common on most systems
today, soft memory errors will happen more often, and with 1GB of
memory as many new systems come equipped with, they are likely to
happen every week or two. Now, you might get lucky most of the time
and these soft memory errors won't affect anything. For example, they
might just turn a single pixel on your screen a different colour for a
moment or two until it's redrawn, or it could even be in an unused
portion of memory. However, the error could also happen in a bit of
the operating system, causing the system to become unstable. Worse
yet, it could happen in an important piece of data, causing you to get
incorrect data for something that needs accuracy.

Point being, these days I would highly recommend ECC memory,
regardless of whether you are looking for a system that needs
registered memory or not.

-------------
Tony Hill
hilla underscore 20 at yahoo dot ca
  #6  
Old October 24th 03, 03:36 AM
Spam Me Please
external usenet poster
 
Posts: n/a
Default


Wow that was a good read. It looks like the tide is turning for a good
reason to purchase ECC memory. I can remember some years back were the
consensus was that ECC was a waste of money because of the low bit
error rate (well that is what some self proclaimed experts said).

It is very interesting to me what you said about memory errors because
I have an old ppro dual motherboard that reports memory errors in the
bios, and it usually has one or two errors over a 3-4 month period.

I guess if anyone goes to the trouble to backup their data, which I do,
they probably want to consider ECC.

Glad you posted that information because looking at the price of ECC
vs Non-ECC the difference is only 20 bucks for one gig of memory. At
least the brand I was looking at. That is for non-buffered ECC memory.
Registered ECC memory costs a lot. Well anything with the name server
on it costs a lot probably for good reasons.

Thanks for the information.

"Tony" == Tony Hill writes:


snip

major snip
  #7  
Old October 24th 03, 05:24 AM
Gary L.
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Posts: n/a
Default

On Fri, 24 Oct 2003 00:29:28 GMT, Tony Hill
wrote:

A quick note about ECC. With Intel's i865 and i875 chipsets, as well
as AMD's new Athlon64 and Opteron chips, ECC is supported by most
systems these days (unfortunately most AthlonXP motherboards do not
support it).


The 875 chip set does support ECC, but the 865 does not. See page 19
of the datasheet:

ftp://download.intel.com/design/chip...s/25252303.pdf

ECC is a GOOD THING! It will detect and correct soft
memory errors. With new systems coming with more and more memory,
soft memory errors are becoming more common. According to a rather
extensive study by IBM, with 256MB of memory you can expect 1 soft
memory per month. With 512MB of memory, as is common on most systems
today, soft memory errors will happen more often, and with 1GB of
memory as many new systems come equipped with, they are likely to
happen every week or two. Now, you might get lucky most of the time
and these soft memory errors won't affect anything. For example, they
might just turn a single pixel on your screen a different colour for a
moment or two until it's redrawn, or it could even be in an unused
portion of memory. However, the error could also happen in a bit of
the operating system, causing the system to become unstable. Worse
yet, it could happen in an important piece of data, causing you to get
incorrect data for something that needs accuracy.

Point being, these days I would highly recommend ECC memory,
regardless of whether you are looking for a system that needs
registered memory or not.


I think the IBM claim is overstated. In my own experience using ECC
systems where the BIOS would log errors, memory errors were very rare
(perhaps one every two or three years). Still, if the board supported
ECC I'd definitely use it.

- -
Gary L.
Reply to the newsgroup only
  #8  
Old October 24th 03, 05:34 AM
Yousuf Khan
external usenet poster
 
Posts: n/a
Default

"Spam Me Please" wrote in message
...

Wow that was a good read. It looks like the tide is turning for a good
reason to purchase ECC memory. I can remember some years back were the
consensus was that ECC was a waste of money because of the low bit
error rate (well that is what some self proclaimed experts said).


Back then "some years back", people weren't routinely running a half a gig
of memory on their home machines. Now they are, so it's a good idea to have
it. Also back then they weren't really using ECC memory, they were using
what is called parity memory. Parity is a less sophisticated form of ECC: it
could report errors but not correct them.

Yousuf Khan


  #9  
Old October 24th 03, 08:22 AM
Tony Hill
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Default

On Thu, 23 Oct 2003 21:24:59 -0700, Gary L. wrote:
On Fri, 24 Oct 2003 00:29:28 GMT, Tony Hill
wrote:

A quick note about ECC. With Intel's i865 and i875 chipsets, as well
as AMD's new Athlon64 and Opteron chips, ECC is supported by most
systems these days (unfortunately most AthlonXP motherboards do not
support it).


The 875 chip set does support ECC, but the 865 does not. See page 19
of the datasheet:

ftp://download.intel.com/design/chip...s/25252303.pdf


Hmm, that's rather interesting, considering that the i875 and i865 are
the same silicon just with different settings. I guess Intel disables
ECC support on the i865 as one of the ways to segment their chipset
market.

Point being, these days I would highly recommend ECC memory,
regardless of whether you are looking for a system that needs
registered memory or not.


I think the IBM claim is overstated. In my own experience using ECC
systems where the BIOS would log errors, memory errors were very rare
(perhaps one every two or three years). Still, if the board supported
ECC I'd definitely use it.


The claims may be somewhat exaggerated, but I don't think that they
are by very much. Unfortunately memory manufacturers no longer seem
to document their soft error rate for memory chips, but even assuming
improvements over the old numbers, with 512MB or 1GB of memory, I
would be surprised if soft memory errors didn't occur on a
semi-regular basis. Of course, there are a lot of things that will
affect the error rate, so it's tough to pin down a single number, but
I still feel that it's worthwhile to get ECC memory these days.

-------------
Tony Hill
hilla underscore 20 at yahoo dot ca
 




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