Buffered Vs Unbuffered memory ?

buffered :  http://en.wikipedia.org/wiki/Registered_memory
note that this is the best type for using many sticks
unbuffered :  http://en.wikipedia.org/wiki/RAM

Since your question asks about unbuffered vs. buffered memory, I'll address that first ... and that add a couple other comments.

Buffered memory has a buffer chip between the address and data bus and the memory chips on the module.  The result is a single memory module presents one "load" to the address and data bus.   An unbuffered module presents one load PER CHIP to the address and data bus -- i.e. 8, 16, or even 32 loads per module.   This can result in notable signal degradation and unreliable memory subsystem operation.   That's why most servers use buffered RAM -- it's simply far more reliable.

As an aside, if you use a desktop board ... or an entry-level "server" board with unbuffered memory -- I never recommend installing more than 2 double-sided memory modules.   Installing more can result in unreliable memory operation.   MANY Windows "glitches" are really undetected memory errors.

Bottom line:  Buffered RAM is far better if you have a choice.   You might want to watch Section 10 of this presentation:  http://www.corsairmemory.com/memory_basics/index.html

A few additional comments ...

Assuming you already have the board you listed, so you don't have any choice about using unbuffered memory, I would use 2 x 2GB modules (to minimize the load on the bus) AND use ECC modules, so you'll know if there's a memory error (and it will correct single-bit errors).   This would be a good choice:  http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=8E8A1CF6A5CA7304

If you don't have the board yet, and want a board that supports large amounts of memory, then I'd look carefully at server boards that support buffered RAM modules.   With buffered RAM you can safely install as many modules as the motherboard supports with no concerns about bus loading.

snnagins so would I have issues with this server board xp pro / Linux dual boot and using that unbuffered memory. Can't return it it's been purchased about 2 months ago you think it's a good board

Thanks

as long as you use only 2 ram sticks (3 max) you should be fine.
i've seen ASUS boards run fine with 4, but as garycase stated, it may turn out bad...

because I just thought about xp 3.5 gb max which made me think of going the route of using 64bit so but over the yrs I've heard alot of issues plus I was considering on using 8gb. Is this not a good choice then eeeeeeek I did buy it at 270us

with 3 x 2 Gb you would have 6 GB ram

You don't want to install 3 modules -- that would keep the board from running in the optimal dual channel mode.

You CAN install 8GB [4 x 2GB] ... but the board MAY slow down the memory access speed (either by reducing the frequency, or by adding a cycle to the latency) to compensate for the added bus loading.   As long as you use ECC modules, this will probably be okay -- the ECC will correct single-bit errors (the most common kind), which will help keep the memory subsystem stable.

By the way, the board's an excellent board => it simply uses a desktop chipset, so doesn't support buffered RAM.

well - what's the performance difference in dual channel ?  i never noticed a difference with the difference in latency; but i can be wrong here..

okay sooo being that if i go that route on getting 4 2gb slots would i need something to adjust the usage of using so much of the memory on that board if it slows down the memory access spped ...

now taht link you gave me garycase does that use ECC modules is there a way to make it so that it wont slow the access speed


snazzy thanks.....

The link I gave you (the Crucial memory) is to ECC modules ... so you'll have as much protection against memory failures as you can get with that board.   The only way to find out if the Asus board slows down the memory access with 4 modules is to simply try it => the manual makes no mention of whether or not the BIOS does this.

However, the manual does note that if you install 3 modules, the system will still run in dual channel mode [although it will be dual channel asymmetric mode rather than the optimal dual channel interleaved mode] => so it won't slow down to single channel mode.

Bottom line:  If you want to max the memory, get 4 of the Crucial 2GB ECC modules.   Install 2 of them (in the blue slots).   Run CPU-Z [http://www.cpuid.com/cpuz.php ] and see what the DRAM frequency and timings are (on the Memory tab).   Shut down and install the other two modules -- then run CPU-Z again and see if the clock or timings have been altered.   If so, the BIOS has automatically adjusted these to help mitigate the deteriorated bus signals caused by the 72 loads that 4 modules place on the bus.   There's really nothing you can do to offset this -- if you change the timings in the BIOS you'll likely have a less reliable memory subsystem.   If the system does slow the memory down a bit, you may want to try installing 3 modules and see what the timings look like for that.

Also, be sure you have ECC enabled in the BIOS => some systems require that you manually enable it -- you certainly don't want to buy ECC memory and not have that feature enabled :-)

IT IS as good board. You can force your board to run on your memory specification. Check on your RAM specification, it should say something like DDR2-800 2-5-5-5-12 1.8V, or a simple 5-5-5-12
The number means that this memory should run fine with CMD 2, CAS 5, RCD 5, RP 5, RAS 12 on frequency 800Mhz and 1.8 volts. Just input those numbers on your board memory configuration, and you should run on your memory best configuration.

The newer board should reduce the penalty of having 4 memory modules. As far as I know, the only problem occurred was with old Athlon64 socket 939, DDR1 RAM. Therefore I could safely say, that the timing should stays the same. If you overclock the memory however, it will go at lower megahertz and looser timings with 4 modules instead of 2. But for non overclocked environment, it should run on advertised timings with no reduction whatsoever.

ASUS server p5m2 .... heres the Ram specs

Total Slots: 4
Capacity: Maximum up to 8GB
Memory Type: Dual Channel ECC / Non-ECC Unbuffered DDR2 533 / 667
Memory Size: 256MB, 512 MB, 1 GB, 2GB


cool one more question  and ill give it a close when i went to purchase the memory for the board in frys (big electronic store) i gave them these exact specs but he gave me Fully buffered memory Dual channell ECC 667 2 2gb sticks that were like 130 bucks does that seem right.... also  does this mean this board can accept Either fully buffered/ Unbuffered whats in bold...  I took that direct from the Asus site with my exact board....

Thanks again

I mean, your RAM specification, not your board supported RAM. DIMM modules should list those number, and you can put those timings at your BIOS. After you obtain your memory module, check your module's manual to find those numbers. Use those numbers on your board.

Fully buffered DIMM is different than buffered DIMM. You need to return that piece. The link garycase provided will give you the correct RAM. Also, a 4GB DIMM requires an x64 OS, otherwise you'll end up with less than 4GB usable RAM.

Sweet thanks I kept on telling the guy that I don't think it's the right but I did purchase 2 sets of them....    From crucial now it's error correcting would that make performance slower then.  Thanks again

Sweet thanks I kept on telling the guy that I don't think it's the right but I did purchase 2 sets of them....    From crucial now it's error correcting would that make performance slower then.  Thanks again