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averydarkplace@yahoo.com
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      04-20-2006, 03:51 PM
My ultimate goal is to build a system that supports a full 4 gigs of
RAM and I don't want to buy the wrong combination of motherboard and
DIMMs. I'm looking to get a motherboard with 4 DIMM slots.

So this leads me to some questions on how to find out what I need:

1) Buffered vs Non Buffered Memory - my understanding is that the
memory control signals can be handled by the module (requires buffered
DIMMS) or by the motherboard's memory contoller (requires non-buffered
DIMMS). So, how do I determine where the buffering needs to take place
and which type of modules to buy? The description for the ASUS
P4P800-E, (and I assume many other MBs) does not specify.

2) Dual Channel Memory Architecture - If the MB supports dual channel
memory, is it requied that the modules be dual channel as well? If I
want a motherboard's four dual channel DIMM slots to hold 1 gigabyte
each (supporting a total of 4 gigs), must each of the modules be dual
channel or single channel?

3) ECC and non-ECC - (aka. "REGISTERED" and "NON REGISTERED") My
understanding is that this is for error correction, and modules with
error correction might be useful for systems that require extra
accuracy, but this will slow down overall performance. So, for most
applications, non-ECC is better. I assume if the MB requirements are
for non-ECC, then I need to get non-ECC dimms. (not really a question,
just stating my understanding)

4) Voltage - There are choices for modules that specify anywhere from
2.3 to 2.95 volts. How important is it to match these reqirements on
the motherboard? I don't see the DIMM voltage specified in any
motherboard specs I've seen.

5) Cas Latency - The ranges I see are from 2 to 3. How much of a
noticeable difference is there between these latencies? How important
is this spec for the average user? What problems will higher latencies
(of 3?) cause?

6) Matching modules - I read that it's best to buy matching modules if
filling more than one DIMM slot. When buying modules sold as pairs, is
there some extra "sameness" then if buying the same modules in separate
packaging? I want to buy 4 modules. Will buying 2 pairs (2x2) of the
same modules be sufficient, or do I need to search for 4 dimms packaged
together? Are there issues with buying two separate pairs from
different manufacturers, for example, a pair of Cruicals, and a pair of
Kingstons?

This is the description of the memory on the ASUS website for the ASUS
P4P800-E DELUXE I'm considering
(http://www.asus.com/products4.aspx?m...&l2=12&l3=30):

- Dual Channel Memory Architecture
- 4 x 184-pin DIMM Sockets
- support max. 4GB DDR400/333/266
- non-ECC DDR SDRAM memory
- ASUS Hyper-Path Technology

Thank you,
~ Avery

 
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Paul
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      04-20-2006, 06:12 PM
In article <(E-Mail Removed) .com>,
(E-Mail Removed) wrote:

Answers inline...

> My ultimate goal is to build a system that supports a full 4 gigs of
> RAM and I don't want to buy the wrong combination of motherboard and
> DIMMs. I'm looking to get a motherboard with 4 DIMM slots.


I'm taking you at your word here, that 3.2GB out of 4GB is simply not
good enough ? If that is the case, you need to find a motherboard that
supports mapping around the memory hole used by the PCI bus and other
resources. These are normally located up near the top of the 32 bit
address space. On Intel, this might be the 955 and 975 chipsets, which
are supposed to support 8GB of RAM. A 64 bit OS would be a good
choice, to complete the project, as even with the mapping function
enabled, WinXP won't be able to use the remapped chunk.

http://support.asus.com.tw/faq/faq_r...Language=en-us

Apparently, the P5WD2 doesn't need to have the mapping function
set up, according to this:

http://support.asus.com.tw/faq/faq_r...Language=en-us

>
> So this leads me to some questions on how to find out what I need:
>
> 1) Buffered vs Non Buffered Memory - my understanding is that the
> memory control signals can be handled by the module (requires buffered
> DIMMS) or by the motherboard's memory contoller (requires non-buffered
> DIMMS). So, how do I determine where the buffering needs to take place
> and which type of modules to buy? The description for the ASUS
> P4P800-E, (and I assume many other MBs) does not specify.


Every Asus manual specifies the memory type. It will mention registered
memory or unbuffered memory. Only a couple manuals glossed over a
detail, as there were a couple Asus boards that could use both, but
the manual only happened to mentioned one type.

The P4P800-E manual says "4GB unbuffered non-ECC DDR400/333/266". And
the manuals can be downloaded from support.asus.com.tw before you
buy a motherboard.

>
> 2) Dual Channel Memory Architecture - If the MB supports dual channel
> memory, is it requied that the modules be dual channel as well? If I
> want a motherboard's four dual channel DIMM slots to hold 1 gigabyte
> each (supporting a total of 4 gigs), must each of the modules be dual
> channel or single channel?


There is no such thing as "dual channel memory". If you were a DIMM
designer, there is only one kind of chips, and there are no special
"dual channel chips" at the memory companies. When a company makes
a "twin-pack" of memory, they reach into a barrel, pull out two tested
DIMMs at random, slap them in the package, and ship it. The sticks
don't know there has been a special ceremony - they are just plain
ordinary DIMMs.

Memory controllers have varying degrees of flexibility, when it comes
to dual channel. For the Nforce2 Northbridge, in fact unmatched DIMMs
can be placed in either channel, and still perform in a dual channel
mode. At the other extreme, are some (SIS or VIA ? don't remember)
chipsets, where only matched pairs would work. Generally speaking,
Intel chipsets are pretty good at it, and even if you put a
screwy combo of RAM in the motherboard, the motherboard will still work
in a virtual single channel mode, so no memory sticks are disabled.

In your example scenario, you could go to Corsair, and buy four of
their singly packaged memory DIMMs, use four of them, and get your
4x1GB configuration. Or you could buy two TwinPacks and achieve the
same result.

>
> 3) ECC and non-ECC - (aka. "REGISTERED" and "NON REGISTERED") My
> understanding is that this is for error correction, and modules with
> error correction might be useful for systems that require extra
> accuracy, but this will slow down overall performance. So, for most
> applications, non-ECC is better. I assume if the MB requirements are
> for non-ECC, then I need to get non-ECC dimms. (not really a question,
> just stating my understanding)


Nope. ECC and registered/unbuffered are independent issues.

ECC typically involves the addition of one chip per side of the
module. An error correcting code uses these extra bits to store the
syndrome (like a checksum in a way). ECC is independent of whether a
module is unbuffered or registered. The commercially available
module configurations would be:

unbuffered non-ECC (the most common at retail)
unbuffered ECC (slightly more expensive, due to the extra chips)
registered ECC (registered modules lightly load the address bus)

I haven't seen any registered non-ECC, as registered memory is more
typically used on server boards, and server users like the certainty
that ECC gives. There would not be a large market for registered
non-ECC (and the non-ECC part could be achieved by disabling ECC in
the BIOS, if necessary).

ECC is typically more valuable with larger memory configurations,
and while people differ in their perception of the need for ECC,
at the 4GB level, you have to start thinking about it. It really
depends on how much you have vested in getting the right answer.
A problem that needs a 4GB memory space, could have a fairly long
run time, like say a logic simulation for example, and maybe it would
be unacceptable to throw away 36 hours of execution time, due to one
tiny error in the memory. If, on the other hand, you are a gamer,
maybe the crash that occurs gives you a chance to get some sleep :-)

As for the efficiency issue, it really depends on whether the processor
is actually capable of working with fractional words on the bus. And
how frequently that happens. If the processor is doing a cache push,
then it bursts full words of data, so no RMW cycles are needed to
fix up the ECC. If the processor has some kind of write combining
function, that further reduces the fractional word traffic on the
bus. So ECC doesn't have to affect that large a percentage of the bus
cycles. I have no idea what percentage impact ECC causes on X86
architecture.

Registered, on the other hand, is a penalty on every transaction.
A registered CAS2 module would perform more like an unbuffered
CAS3 module - due to the 1 cycle delay through the register chip
on the memory module. Basically, the first cycle latency is
increased by one, but the performance of the data burst is
unaffected.

>
> 4) Voltage - There are choices for modules that specify anywhere from
> 2.3 to 2.95 volts. How important is it to match these reqirements on
> the motherboard? I don't see the DIMM voltage specified in any
> motherboard specs I've seen.


Many manuals will give a range, but the percentage that give
full details is not that large. I would not count on Asus to tell
you the whole truth on this.

What the BIOS shows, and what the hardware is capable of, do not
have to match. It is possible for two BIOS voltage values, to
cause the same hardware bit settings to occur, so unless the DIMM
voltage is displayed in the hardware monitor, you won't really
know for sure what it is doing.

When a memory manufacturer specifies a voltage, it really depends on
how the module was constructed, as to how important that voltage is.
JEDEC states that a DDR400 memory module gets 2.6V. Memory with a
2.7V spec, is quite likely to be a "non-voltage-loving" module, and
a user would be unwise to crank it. There are other modules, like
Redline, where perhaps 3.3V or higher was speced. That says, "we
really need the voltage to meet our mighty spec", so you would
expect to need to apply most of that to get it to work half
decent. And whether high voltages are safe to apply, may depend on
whether the memory chips have internal voltage regulation, or
whether the chips are truly tolerant of very large voltages.
In some cases, the memory controller cannot take those kinds
of voltages, as some Athlon64 FX owners have discovered.

>
> 5) Cas Latency - The ranges I see are from 2 to 3. How much of a
> noticeable difference is there between these latencies? How important
> is this spec for the average user? What problems will higher latencies
> (of 3?) cause?


In these benchmarks, Winrar loves CAS, but many other applications
don't seem to care. If you only do Winrar all day, buy a low CAS
memory :-)

http://www.tomshardware.com/2004/01/...ns/page10.html

>
> 6) Matching modules - I read that it's best to buy matching modules if
> filling more than one DIMM slot. When buying modules sold as pairs, is
> there some extra "sameness" then if buying the same modules in separate
> packaging? I want to buy 4 modules. Will buying 2 pairs (2x2) of the
> same modules be sufficient, or do I need to search for 4 dimms packaged
> together? Are there issues with buying two separate pairs from
> different manufacturers, for example, a pair of Cruicals, and a pair of
> Kingstons?
>
> This is the description of the memory on the ASUS website for the ASUS
> P4P800-E DELUXE I'm considering
> (http://www.asus.com/products4.aspx?m...&l2=12&l3=30):
>
> - Dual Channel Memory Architecture
> - 4 x 184-pin DIMM Sockets
> - support max. 4GB DDR400/333/266
> - non-ECC DDR SDRAM memory
> - ASUS Hyper-Path Technology
>
> Thank you,
> ~ Avery


AFAIK, you won't find four DIMMs in one pack. So you have to get
two TwinPaks anyway. (And I don't feel like writing another page
of stuff, so just buy the memory already...)

If you put 4x1GB unbuffered non-ECC into your P4P800-E Deluxe,
you'll probably get to use about 3.2GB of it or so. Using
a PCI video card, would perhaps free up a bit more of it. The
865/875 generation chipsets, don't have remapping, so using a 64 bit OS
is not going to help in this case. On the Intel side, you'll need
a motherboard with a 955 or 975 chipset, and some DDR2 memory.
That means you'll be moving to a PCI Express video card and so on.

If you wanted ECC support, you'd need a P4C800 family motherboard
and the 875 chipset. I don't think the P4P800-E has ECC support.

The Athlon64 has the memory remapping functon, so it is possible
to use the entire 4GB on that platform, assuming the BIOS you install
has the enabling function for the mapper. This mapping function
is not typically shown in the Asus user manual, and the BIOS
may gain the function around the fourth or fifth BIOS release
for the board.

Paul
 
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Mark A
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Posts: n/a
 
      04-20-2006, 06:26 PM

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> My ultimate goal is to build a system that supports a full 4 gigs of
> RAM and I don't want to buy the wrong combination of motherboard and
> DIMMs. I'm looking to get a motherboard with 4 DIMM slots.
>
> So this leads me to some questions on how to find out what I need:
>
> 1) Buffered vs Non Buffered Memory - my understanding is that the
> memory control signals can be handled by the module (requires buffered
> DIMMS) or by the motherboard's memory contoller (requires non-buffered
> DIMMS). So, how do I determine where the buffering needs to take place
> and which type of modules to buy? The description for the ASUS
> P4P800-E, (and I assume many other MBs) does not specify.
>
> 2) Dual Channel Memory Architecture - If the MB supports dual channel
> memory, is it requied that the modules be dual channel as well? If I
> want a motherboard's four dual channel DIMM slots to hold 1 gigabyte
> each (supporting a total of 4 gigs), must each of the modules be dual
> channel or single channel?
>
> 3) ECC and non-ECC - (aka. "REGISTERED" and "NON REGISTERED") My
> understanding is that this is for error correction, and modules with
> error correction might be useful for systems that require extra
> accuracy, but this will slow down overall performance. So, for most
> applications, non-ECC is better. I assume if the MB requirements are
> for non-ECC, then I need to get non-ECC dimms. (not really a question,
> just stating my understanding)
>
> 4) Voltage - There are choices for modules that specify anywhere from
> 2.3 to 2.95 volts. How important is it to match these reqirements on
> the motherboard? I don't see the DIMM voltage specified in any
> motherboard specs I've seen.
>
> 5) Cas Latency - The ranges I see are from 2 to 3. How much of a
> noticeable difference is there between these latencies? How important
> is this spec for the average user? What problems will higher latencies
> (of 3?) cause?
>
> 6) Matching modules - I read that it's best to buy matching modules if
> filling more than one DIMM slot. When buying modules sold as pairs, is
> there some extra "sameness" then if buying the same modules in separate
> packaging? I want to buy 4 modules. Will buying 2 pairs (2x2) of the
> same modules be sufficient, or do I need to search for 4 dimms packaged
> together? Are there issues with buying two separate pairs from
> different manufacturers, for example, a pair of Cruicals, and a pair of
> Kingstons?
>
> This is the description of the memory on the ASUS website for the ASUS
> P4P800-E DELUXE I'm considering
> (http://www.asus.com/products4.aspx?m...&l2=12&l3=30):
>
> - Dual Channel Memory Architecture
> - 4 x 184-pin DIMM Sockets
> - support max. 4GB DDR400/333/266
> - non-ECC DDR SDRAM memory
> - ASUS Hyper-Path Technology
>
> Thank you,
> ~ Avery
>


1. For most users, get unbuffered. Only in certain high end servers where
data integrity is more important than speed is buffered needed.

2. You need 4 x 1GB DIMMS, 184-pin DDR400 (PC3200) dual channel memory. You
can get 4 sticks of 1 GB, or 2 pairs of 2 GB (2 x 1 GB per pair)..

3. Yes, you are correct. Similar to number 1 above.

4. You can change the DIMM voltage in the computer system bios.

5. Usually not critical, but if you building a 4 GB machine, you must be
very concerned about performance, so get the fastest you can afford. You set
the timings in the bios, otherwise you get the defaults. If you buy "value
memory" the defaults are OK, but if you buy faster memory you will want to
set the timings to faster settings in the system bios (check the memory
manufacturer website for more information).

6. Matching modules are tested together in dual channel mode before
packaging to make sure they are compatible (at least the ones from Corsair
are). This decreases the likelihood of mismatches, and the cost is usually
about the same, so I would get matching pairs. Make sure that you install
the matching pair DIMMS in the same channel (which could be slots 1 and 2,
or 1 and 3, etc, depending on how your mb is designed). You only need
matching "pairs" (not quads) since the dual channel architecture is
implemented across one pair (2 DIMMS), even if you have 4 DIMMS total. Dual
Channel memory is not sold in quads (which is why it is call "Dual"). If you
know anything about disk striping or RAID, dual channel memory uses the same
concept to work faster, but dual channel memory only works in pairs.



 
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Bob Willard
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      04-20-2006, 07:30 PM
I agree with everything Paul wrote, except for the importance of ECC.
ECC delivers single-bit error correction and double-bit error detection
which takes care IMHO of all common RAM errors. Without ECC, however,
the result of a single-bit error (caused, say, by an alpha particle)
is not likely to be a crash, and may be something far worse. If an
error occurs on a data read, the bad data is accepted by the CPU and
the error is propagated with no detection. If any error occurs on an
instruction read and the mis-read instruction is valid, then that
mis-read instruction will be executed instead of the real instruction
and bad results will be propagated without detection.

For a gaming PC, I don't suggest paying extra for ECC. But for any PC
which deals with data that has any real value to the PC's owner, then
I always pay the modest increment to get ECC RAM. And that's why this
PC uses a P4C instead of a P4P MB.

--
Cheers, Bob
 
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