Memory Configuration

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Walmsley

Hi

Can somebody please explain to me all this stuff about Memory.

I'm getting an asus p4p800 and I've asked for a single module of PC3200 DDR
400mhz 512RAM. The quote came through and mentioned 2x256MB modules.

I've downloaded the manual from Asus and it makes various references to SDR
and DDR, depending on the configuration used. Am I missing something, or is
there an advantage in having separate memory modules? I always thought the
more memory sockets left free, the better (for expandability)?

The manual says that "DIMMS installed in any three sockets will function in
single channel mode"

I'm assuming I want Double channel mode (sounds faster to me!)

I suppose I really don't "get" the whole DDR/SDR principle, and single/dual
channel configurations.

I'd appreciate this whole principle being explained to me, but bottom line
is:- On my ASUS P4P800, to run with an 800mhz FSB, and PC3200 DDR memory at
400mhz FSB, what is the fastest/best configuration? 1x512MB module, or
2x256MB modules?

Thanks in advance.

Nik.

_____________________________________________________
*** Remove SPAMKILL from my Email Address to reply via Email ***
_____________________________________________________
 
Use two MATCHED 256 MB DDR RAM sticks running in dual channel mode for the
fastest memory data transfer.
 
"Walmsley" said:
Hi

Can somebody please explain to me all this stuff about Memory.

I'm getting an asus p4p800 and I've asked for a single module of PC3200 DDR
400mhz 512RAM. The quote came through and mentioned 2x256MB modules.

I've downloaded the manual from Asus and it makes various references to SDR
and DDR, depending on the configuration used. Am I missing something, or is
there an advantage in having separate memory modules? I always thought the
more memory sockets left free, the better (for expandability)?

The manual says that "DIMMS installed in any three sockets will function in
single channel mode"

I'm assuming I want Double channel mode (sounds faster to me!)

I suppose I really don't "get" the whole DDR/SDR principle, and single/dual
channel configurations.

I'd appreciate this whole principle being explained to me, but bottom line
is:- On my ASUS P4P800, to run with an 800mhz FSB, and PC3200 DDR memory at
400mhz FSB, what is the fastest/best configuration? 1x512MB module, or
2x256MB modules?

Thanks in advance.

Nik.
Click to expand...

You want "dual channel mode". It will give you about 30% more
bandwidth, as measured by mmetest86. (That is from an experiment
I did before Christmas with an 865PE.)

SDR transfers 1 piece of data per clock cycle
DDR transfers 2 pieces of data per clock cycle
Dual channel DDR transfers 4 pieces of data per clock cycle

Data is not transferred all the time, as time is needed to
transfer commands to the memory module, before data can flow.
There are limits to how "efficient" any of the three modes
above can be, as the processor likes to transfer data in
cache line size chunks, and there are gaps between bursts
of data.

So, having 2x256 identical modules installed in dual channel
mode on a P4P800 is better than 1x512.

Intel has this guide to the various memory configurations
possible with 875/865 chipsets. While it isn't listed,
perhaps two sticks of PC4000 with a clock ratio of 1:1
and a 25% overclocked processor, gives the fastest transfer.
If you want four sticks of memory, it is hard to run the
memory bus at as high a speed as you can with two sticks.
In that case, four sticks of PC3200/PC3500 or so, with
a clock ratio of 5:4 and a 25% overclocked processor, gives
the next fastest transfer.

ftp://download.intel.com/design/chipsets/applnots/25273001.pdf

Four double sided sticks allow more pages of memory to remain
open, and that configuration is the one at the top of the
Intel chart on page 13. A so-called "open page" is handy,
because the command overhead to get some more data is less
than it would be if the page is closed.

On the machine I was building, I wasted considerable time with
my vendor, getting two identical pieces of memory, and the
vendor didn't even understand why I wanted 2x256 instead
of 1x512. The guy should have been running a flower shop :-)

HTH,
Paul
 
That's great, I knew I was asking the right guys.

Thanks very much for that.

Nik.
_____________________________________________________
*** Remove SPAMKILL from my Email Address to reply via Email ***
_____________________________________________________
"Walmsley" said:
Hi

Can somebody please explain to me all this stuff about Memory.

I'm getting an asus p4p800 and I've asked for a single module of PC3200 DDR
400mhz 512RAM. The quote came through and mentioned 2x256MB modules.

I've downloaded the manual from Asus and it makes various references to SDR
and DDR, depending on the configuration used. Am I missing something, or is
there an advantage in having separate memory modules? I always thought the
more memory sockets left free, the better (for expandability)?

The manual says that "DIMMS installed in any three sockets will function in
single channel mode"

I'm assuming I want Double channel mode (sounds faster to me!)

I suppose I really don't "get" the whole DDR/SDR principle, and single/dual
channel configurations.

I'd appreciate this whole principle being explained to me, but bottom line
is:- On my ASUS P4P800, to run with an 800mhz FSB, and PC3200 DDR memory at
400mhz FSB, what is the fastest/best configuration? 1x512MB module, or
2x256MB modules?

Thanks in advance.

Nik.
Click to expand...

You want "dual channel mode". It will give you about 30% more
bandwidth, as measured by mmetest86. (That is from an experiment
I did before Christmas with an 865PE.)

SDR transfers 1 piece of data per clock cycle
DDR transfers 2 pieces of data per clock cycle
Dual channel DDR transfers 4 pieces of data per clock cycle

Data is not transferred all the time, as time is needed to
transfer commands to the memory module, before data can flow.
There are limits to how "efficient" any of the three modes
above can be, as the processor likes to transfer data in
cache line size chunks, and there are gaps between bursts
of data.

So, having 2x256 identical modules installed in dual channel
mode on a P4P800 is better than 1x512.

Intel has this guide to the various memory configurations
possible with 875/865 chipsets. While it isn't listed,
perhaps two sticks of PC4000 with a clock ratio of 1:1
and a 25% overclocked processor, gives the fastest transfer.
If you want four sticks of memory, it is hard to run the
memory bus at as high a speed as you can with two sticks.
In that case, four sticks of PC3200/PC3500 or so, with
a clock ratio of 5:4 and a 25% overclocked processor, gives
the next fastest transfer.

ftp://download.intel.com/design/chipsets/applnots/25273001.pdf

Four double sided sticks allow more pages of memory to remain
open, and that configuration is the one at the top of the
Intel chart on page 13. A so-called "open page" is handy,
because the command overhead to get some more data is less
than it would be if the page is closed.

On the machine I was building, I wasted considerable time with
my vendor, getting two identical pieces of memory, and the
vendor didn't even understand why I wanted 2x256 instead
of 1x512. The guy should have been running a flower shop :-)

HTH,
Paul
 
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