Memory compatibility?

Puddin' Man wrote:
Just about 1 year ago, I built a desktop based on:

Intel i5-650
Asus P7H55D-M EVO
G.SKILL Ripjaws Series 4GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model
F3-12800CL9D-4GBRL
etc

The Ripjaws mem tested OK with memtest86+. The system has been doing well for the last
year.

Newegg now has a sale on:

G.SKILL Ripjaws Series 4GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model
F3-12800CL9S-4GBRL

for $34. Note that the "old" is 9D, the "new" is 9S.

I can't discern any difference in the specs:

"old" - http://www.gskill.com/products.php?index=222
"new" -
http://www.newegg.com/Product/Produc...6&SID=FW9wkedl
(apologies for wrap)

The Asus P7H55D-M EVO has 2 empty dimm slots. Any reason -not- to expect full
compatibility between the old and new Ripjaws mem?

Thx,
P

One product consists of (2) 2GB sticks, while the other is (1) 4GB stick ?

Maybe the "D" stands for Dual, the "S" for Single ?

Check the vip.asus.com forums, or use the Newegg reviews for your P7H55D-M EVO
motherboard, to see how well 4GB sticks work.

Paul

On Tue, 07 Jun 2011 16:01:51 -0400, Paul wrote:

One product consists of (2) 2GB sticks, while the other is (1) 4GB stick ?

It appears you are correct. I missed the obvious.

Maybe the "D" stands for Dual, the "S" for Single ?

Less certain about that.

Check the vip.asus.com forums, or use the Newegg reviews for your P7H55D-M EVO
motherboard, to see how well 4GB sticks work.

The reviews looked very good, but mine is a dual-channel design, and, as I
recall, a 4gb stick would unbalance it. Prefer not to go that route.

Many Thanks,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Puddin' Man wrote:
On Tue, 07 Jun 2011 16:01:51 -0400, Paul wrote:

One product consists of (2) 2GB sticks, while the other is (1) 4GB stick ?

It appears you are correct. I missed the obvious.

Maybe the "D" stands for Dual, the "S" for Single ?

Less certain about that.

Check the vip.asus.com forums, or use the Newegg reviews for your P7H55D-M EVO
motherboard, to see how well 4GB sticks work.

The reviews looked very good, but mine is a dual-channel design, and, as I
recall, a 4gb stick would unbalance it. Prefer not to go that route.

Many Thanks,
P


You could use 2x2GB plus 2x4GB. The speed would be adjusted to the
slowest pair of modules. A slight correction may be required with
four modules - if memory testing shows a problem, you can make
a slight adjustment (bump up CAS one notch, use extra VDimm,
command rate is probably already 2N, drop memory bus clock
rate one notch). Don't boot into Windows, until memtest86+ is
passing clean.

Paul

On Tue, 07 Jun 2011 18:12:10 -0400, Paul wrote:

Puddin' Man wrote:
On Tue, 07 Jun 2011 16:01:51 -0400, Paul wrote:

One product consists of (2) 2GB sticks, while the other is (1) 4GB stick ?

It appears you are correct. I missed the obvious.

Maybe the "D" stands for Dual, the "S" for Single ?

Less certain about that.

Check the vip.asus.com forums, or use the Newegg reviews for your P7H55D-M EVO
motherboard, to see how well 4GB sticks work.

The reviews looked very good, but mine is a dual-channel design, and, as I
recall, a 4gb stick would unbalance it. Prefer not to go that route.

Many Thanks,
P


You could use 2x2GB plus 2x4GB. The speed would be adjusted to the
slowest pair of modules. A slight correction may be required with
four modules - if memory testing shows a problem, you can make
a slight adjustment (bump up CAS one notch, use extra VDimm,
command rate is probably already 2N, drop memory bus clock
rate one notch). Don't boot into Windows, until memtest86+ is
passing clean.

At least 3 full iterations.

Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Puddin' Man wrote:


Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P

I like to keep my modules in pairs, as it would make potential resale
easier.

If you look in section 2.4.2 of the manual ("Memory Configurations"
or something similar), you'll likely see that the memory controller
supports flex memory.

You can use three DIMMs, like this. Two DIMMs go on one channel, and
one DIMM on the other channel. Memory quantity in each channel is
equal, which means it's "dual channel from top to bottom". Memory
speed would be reflective of a 4 stick configuration, as the
more heavily loaded channel limits how aggressively it can be set up.

2GB 4GB
2GB

Another thing you can do, is tolerate this kind of configuration.

2GB 4GB

In that case, the lower 2GB+2GB of memory space is dual channel, while
the last remaining 2GB on the right, runs single channel. This makes the
bandwidth performance of the memory, location specific. The
computer still works. (I tested this about five years ago, on
one of my computers, and couldn't detect which memory space I was
in, based on the observed speed.)

So you can do just about anything you want with it.

If it was mine, I'd run it like this

4GB 4GB

and save the 2x2GB in a drawer for later. If the 4GB modules fail,
you have some spare memory on hand. Or, if you decide some day to test
12GB, again, you can do it. (I prefer to run my machines with two sticks,
and have done so, on the last four computers.)

4GB 4GB
2GB 2GB

HTH,
Paul

On Wed, 08 Jun 2011 03:07:52 -0400, Paul wrote:

Puddin' Man wrote:


Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P

I like to keep my modules in pairs, as it would make potential resale
easier.

There are numerous advantages in keeping modules in pairs.

If you look in section 2.4.2 of the manual ("Memory Configurations"
or something similar), you'll likely see that the memory controller
supports flex memory.

I cannot count the Asus manual as the definitive authority on the
memory controller as it resides in the 45nm "half" of my i5-650
cpu die and lies in the "Domain of Intel", not Asus.

You can use three DIMMs, like this. Two DIMMs go on one channel, and
one DIMM on the other channel. Memory quantity in each channel is
equal, which means it's "dual channel from top to bottom". Memory
speed would be reflective of a 4 stick configuration, as the
more heavily loaded channel limits how aggressively it can be set up.

2GB 4GB
2GB

A literal reading indicates you are correct in this. I was assuming
it somehow mapped the mem by dimm sockets. The manual indicates any
combination of 1, 2, and 4gb modules are OK and dual-channel performance
is totally maintained whenever mem capacity in both channels is equal.

Another thing you can do, is tolerate this kind of configuration.

2GB 4GB

In that case, the lower 2GB+2GB of memory space is dual channel, while
the last remaining 2GB on the right, runs single channel. This makes the
bandwidth performance of the memory, location specific. The
computer still works. (I tested this about five years ago, on
one of my computers, and couldn't detect which memory space I was
in, based on the observed speed.)

You couldn't discern a difference between single and dual-channel performance?

I don't follow you on this. If you have 2gb in channel A and 4gb in channel B:

a.) It is dual-channel unbalanced.
b.) According to the manual, the board maps 2gb from each channel as dual-
channel, and the excess 2gb in channel B as single-channel (per section 2.4.2).


So you can do just about anything you want with it.

Subject to certain performance constraints.

If it was mine, I'd run it like this

4GB 4GB

and save the 2x2GB in a drawer for later. If the 4GB modules fail,
you have some spare memory on hand. Or, if you decide some day to test
12GB, again, you can do it. (I prefer to run my machines with two sticks,
and have done so, on the last four computers.)

4GB 4GB
2GB 2GB

There are certain advantages in so doing. If the 4gb modules were selling
for, say, $12 each ...

Cheers,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Puddin' Man wrote:
On Wed, 08 Jun 2011 03:07:52 -0400, Paul wrote:

Puddin' Man wrote:

Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P
I like to keep my modules in pairs, as it would make potential resale
easier.

There are numerous advantages in keeping modules in pairs.

If you look in section 2.4.2 of the manual ("Memory Configurations"
or something similar), you'll likely see that the memory controller
supports flex memory.

I cannot count the Asus manual as the definitive authority on the
memory controller as it resides in the 45nm "half" of my i5-650
cpu die and lies in the "Domain of Intel", not Asus.

You have the option of downloading the datasheet for the Intel processor
and verifying the existence of a flex memory controller. When Asus writes
the manual, they too would have access to the datasheet, and how the memory
(and BIOS setup code) works.

I'd download the file myself and look, but it means booting up a VM
and viewing the PDF there. (I use a certain version of Acrobat Reader,
as the newest versions, suck. Intel PDF documents now require the latest
Reader.)


You can use three DIMMs, like this. Two DIMMs go on one channel, and
one DIMM on the other channel. Memory quantity in each channel is
equal, which means it's "dual channel from top to bottom". Memory
speed would be reflective of a 4 stick configuration, as the
more heavily loaded channel limits how aggressively it can be set up.

2GB 4GB
2GB

A literal reading indicates you are correct in this. I was assuming
it somehow mapped the mem by dimm sockets. The manual indicates any
combination of 1, 2, and 4gb modules are OK and dual-channel performance
is totally maintained whenever mem capacity in both channels is equal.

There are two implementations of dual channel in existence. The AMD
version, used to make a "128 bit wide DIMM" from two DIMMs, and that
method implied a need to match modules religiously.

The other method, is to have a memory controller per DIMM, and
when an access request comes in, the mapping logic determines
which controller responds. In the 2+2 versus 4GB DIMM case,
the "hits" fall in the appropriate place, and alternate between
channels. Since accesses tend to involve cache line sized requests,
there aren't really any "boundary" conditions to speak of.

When you have mismatched amounts of memory on each channel,
the requests are all answered by a single controller on one
channel, when there is no memory across from it.

The Flex memory setup, always does the best it can (i.e. you
can't "build a better one"). And all it needs to do that, is
for the hardware (controllers) to be set up properly, so that
a continuous physical memory map exists (i.e. don't have
two controllers respond to the same absolute address).


Another thing you can do, is tolerate this kind of configuration.

2GB 4GB

In that case, the lower 2GB+2GB of memory space is dual channel, while
the last remaining 2GB on the right, runs single channel. This makes the
bandwidth performance of the memory, location specific. The
computer still works. (I tested this about five years ago, on
one of my computers, and couldn't detect which memory space I was
in, based on the observed speed.)

You couldn't discern a difference between single and dual-channel performance?

I don't follow you on this. If you have 2gb in channel A and 4gb in channel B:

a.) It is dual-channel unbalanced.
b.) According to the manual, the board maps 2gb from each channel as dual-
channel, and the excess 2gb in channel B as single-channel (per section 2.4.2).

I was able to use a specially modified copy of memtest86+, to verify
my memory controller actually worked that way. The dual channel section
of the memory space, ran 1400MB/sec, while the single channel section of the
memory space, ran 900MB/sec. (That gives you some idea how long ago this was.)
The memory config looked like this.

512MB --- remaining memory runs at single channel rates
512MB 512MB --- dual channel memory space

What I'm saying is, when running applications in Windows, if you're blindfolded,
you can't tell which portion of that space you're using at the moment. Even
though there is a 500MB/sec difference in memory bandwidth, the L1 and L2
cache tend to hide the details. It feels just as smooth, as if the
machine was running fully at 1400MB/sec.

The benchmark application can detect the difference, and I used memtest86+
because it works with physical memory addresses, and I could be absolutely
sure of what I was testing. The code change required adding three lines
to the source, to print additional information to the memtest screen.


So you can do just about anything you want with it.

Subject to certain performance constraints.

Pre-built computers are frequently shipped with "stupid" configurations,
which takes advantage of Flex memory, and nobody is the wiser.


If it was mine, I'd run it like this

4GB 4GB

and save the 2x2GB in a drawer for later. If the 4GB modules fail,
you have some spare memory on hand. Or, if you decide some day to test
12GB, again, you can do it. (I prefer to run my machines with two sticks,
and have done so, on the last four computers.)

4GB 4GB
2GB 2GB

There are certain advantages in so doing. If the 4gb modules were selling
for, say, $12 each ...

Cheers,
P

So you're saying, you don't appreciate the fact you're getting a
gigabyte of memory for roughly $10 ? How many things can you buy at the
store today, that are falling in price ? I went to Home Depot the
other day, to price a four foot length of tubular steel, and
they wanted close to $16 for it. Luckily for us, memory is
still headed in the opposite direction. And it's not
even clear, why that is happening. You'd think with
Japan all messed up, there'd be some price gouging.

Paul

On Wed, 08 Jun 2011 19:34:45 -0400, Paul wrote:

Puddin' Man wrote:
On Wed, 08 Jun 2011 03:07:52 -0400, Paul wrote:

Puddin' Man wrote:

Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P
I like to keep my modules in pairs, as it would make potential resale
easier.

There are numerous advantages in keeping modules in pairs.

If you look in section 2.4.2 of the manual ("Memory Configurations"
or something similar), you'll likely see that the memory controller
supports flex memory.

Note ref to "memory controller" (singular).

I cannot count the Asus manual as the definitive authority on the
memory controller as it resides in the 45nm "half" of my i5-650
cpu die and lies in the "Domain of Intel", not Asus.

You have the option of downloading the datasheet for the Intel processor
and verifying the existence of a flex memory controller. When Asus writes
the manual, they too would have access to the datasheet, and how the memory
(and BIOS setup code) works.

I'd download the file myself and look, but it means booting up a VM
and viewing the PDF there. (I use a certain version of Acrobat Reader,
as the newest versions, suck. Intel PDF documents now require the latest
Reader.)

That's hardly necessary. However, I'll briefly mention that the datasheet
is written in (hopefully, hopefully) understandable American-English,
while the Asus manual is written in (very ambitious) Taiwanese-English,
thereby leaving considerable margin for less-than-perfect interpretation(s). :-)


You can use three DIMMs, like this. Two DIMMs go on one channel, and
one DIMM on the other channel. Memory quantity in each channel is
equal, which means it's "dual channel from top to bottom". Memory
speed would be reflective of a 4 stick configuration, as the
more heavily loaded channel limits how aggressively it can be set up.

2GB 4GB
2GB

A literal reading indicates you are correct in this. I was assuming
it somehow mapped the mem by dimm sockets. The manual indicates any
combination of 1, 2, and 4gb modules are OK and dual-channel performance
is totally maintained whenever mem capacity in both channels is equal.

There are two implementations of dual channel in existence. The AMD
version, used to make a "128 bit wide DIMM" from two DIMMs, and that
method implied a need to match modules religiously.

This is likely what I was previously thinking of.

The other method, is to have a memory controller per DIMM, and

"a memory controller per DIMM"??? Uh-oh, we could have difficulties,
here. :-)

when an access request comes in, the mapping logic determines
which controller responds.

Note ref to "which controller" (implies several).

In the 2+2 versus 4GB DIMM case,
the "hits" fall in the appropriate place, and alternate between
channels. Since accesses tend to involve cache line sized requests,
there aren't really any "boundary" conditions to speak of.

When you have mismatched amounts of memory on each channel,
the requests are all answered by a single controller on one
channel, when there is no memory across from it.

This statement seems to contradict itself. If there is -some-
volume of memory on each channel, there cannot be an absence
of memory on any adjacent channel.

The Flex memory setup, always does the best it can (i.e. you
can't "build a better one"). And all it needs to do that, is
for the hardware (controllers) to be set up properly, so that
a continuous physical memory map exists (i.e. don't have
two controllers respond to the same absolute address).

Note ref to "memory controllers" (plural).


Another thing you can do, is tolerate this kind of configuration.

2GB 4GB

In that case, the lower 2GB+2GB of memory space is dual channel, while
the last remaining 2GB on the right, runs single channel. This makes the
bandwidth performance of the memory, location specific. The
computer still works. (I tested this about five years ago, on
one of my computers, and couldn't detect which memory space I was
in, based on the observed speed.)

You couldn't discern a difference between single and dual-channel performance?

I don't follow you on this. If you have 2gb in channel A and 4gb in channel B:

a.) It is dual-channel unbalanced.
b.) According to the manual, the board maps 2gb from each channel as dual-
channel, and the excess 2gb in channel B as single-channel (per section 2.4.2).

I was able to use a specially modified copy of memtest86+, to verify
my memory controller actually worked that way. The dual channel section
of the memory space, ran 1400MB/sec, while the single channel section of the
memory space, ran 900MB/sec. (That gives you some idea how long ago this was.)
The memory config looked like this.

512MB --- remaining memory runs at single channel rates
512MB 512MB --- dual channel memory space

What I'm saying is, when running applications in Windows, if you're blindfolded,
you can't tell which portion of that space you're using at the moment. Even
though there is a 500MB/sec difference in memory bandwidth, the L1 and L2
cache tend to hide the details. It feels just as smooth, as if the
machine was running fully at 1400MB/sec.

Check.

The benchmark application can detect the difference, and I used memtest86+
because it works with physical memory addresses, and I could be absolutely
sure of what I was testing. The code change required adding three lines
to the source, to print additional information to the memtest screen.

Neat.

So you can do just about anything you want with it.

Subject to certain performance constraints.

Pre-built computers are frequently shipped with "stupid" configurations,
which takes advantage of Flex memory, and nobody is the wiser.

One reason why we build.


If it was mine, I'd run it like this

4GB 4GB

and save the 2x2GB in a drawer for later. If the 4GB modules fail,
you have some spare memory on hand. Or, if you decide some day to test
12GB, again, you can do it. (I prefer to run my machines with two sticks,
and have done so, on the last four computers.)

4GB 4GB
2GB 2GB

There are certain advantages in so doing. If the 4gb modules were selling
for, say, $12 each ...

Cheers,
P

So you're saying, you don't appreciate the fact you're getting a
gigabyte of memory for roughly $10 ?

Actually a bit less. $34/4 = $8.50.

How many things can you buy at the
store today, that are falling in price ? I went to Home Depot the
other day, to price a four foot length of tubular steel, and
they wanted close to $16 for it.

Yeah, it's been like that around here for years. Vicious price increases
and strictly comical gov't efforts to lie about it.

Luckily for us, memory is
still headed in the opposite direction. And it's not
even clear, why that is happening. You'd think with
Japan all messed up, there'd be some price gouging.

Most memory is made in non-Nipponese Asian locales?

For the record, I -have- to appreciate the $8.50/gb price because
I cannot forget having to pay ~ $110/4 = $27.50/gb for it 13 months
ago. There was a "spike", and I needed to complete/test a build.

But I have to justify expense on pc resources according to expectations of
usage. If the "sweet spot" for my little desktop is expected to be around 8gb
physical mem, it's hard to justify the additional expense of an added 4gb, if
only $34.

Prost,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Puddin' Man wrote:
On Wed, 08 Jun 2011 19:34:45 -0400, Paul wrote:

Puddin' Man wrote:
On Wed, 08 Jun 2011 03:07:52 -0400, Paul wrote:

Puddin' Man wrote:

Worth considering, I guess, but I'm not sure I'm gonna need 12 gb
in the long run. Suspect 8 gb would be sufficient.

Somewhat curious that the same 2x2GB that I originally installed
is now priced at $47.99 while the "equivalent" 1x4GB is down to $34.
Maybe they'll price the 2x2GB down as well before it's all over.

Best,
P
I like to keep my modules in pairs, as it would make potential resale
easier.
There are numerous advantages in keeping modules in pairs.

If you look in section 2.4.2 of the manual ("Memory Configurations"
or something similar), you'll likely see that the memory controller
supports flex memory.

Note ref to "memory controller" (singular).

I cannot count the Asus manual as the definitive authority on the
memory controller as it resides in the 45nm "half" of my i5-650
cpu die and lies in the "Domain of Intel", not Asus.
You have the option of downloading the datasheet for the Intel processor
and verifying the existence of a flex memory controller. When Asus writes
the manual, they too would have access to the datasheet, and how the memory
(and BIOS setup code) works.

I'd download the file myself and look, but it means booting up a VM
and viewing the PDF there. (I use a certain version of Acrobat Reader,
as the newest versions, suck. Intel PDF documents now require the latest
Reader.)

That's hardly necessary. However, I'll briefly mention that the datasheet
is written in (hopefully, hopefully) understandable American-English,
while the Asus manual is written in (very ambitious) Taiwanese-English,
thereby leaving considerable margin for less-than-perfect interpretation(s). :-)

You can use three DIMMs, like this. Two DIMMs go on one channel, and
one DIMM on the other channel. Memory quantity in each channel is
equal, which means it's "dual channel from top to bottom". Memory
speed would be reflective of a 4 stick configuration, as the
more heavily loaded channel limits how aggressively it can be set up.

2GB 4GB
2GB
A literal reading indicates you are correct in this. I was assuming
it somehow mapped the mem by dimm sockets. The manual indicates any
combination of 1, 2, and 4gb modules are OK and dual-channel performance
is totally maintained whenever mem capacity in both channels is equal.
There are two implementations of dual channel in existence. The AMD
version, used to make a "128 bit wide DIMM" from two DIMMs, and that
method implied a need to match modules religiously.

This is likely what I was previously thinking of.

The other method, is to have a memory controller per DIMM, and

"a memory controller per DIMM"??? Uh-oh, we could have difficulties,
here. :-)

when an access request comes in, the mapping logic determines
which controller responds.

Note ref to "which controller" (implies several).

In the 2+2 versus 4GB DIMM case,
the "hits" fall in the appropriate place, and alternate between
channels. Since accesses tend to involve cache line sized requests,
there aren't really any "boundary" conditions to speak of.

When you have mismatched amounts of memory on each channel,
the requests are all answered by a single controller on one
channel, when there is no memory across from it.

This statement seems to contradict itself. If there is -some-
volume of memory on each channel, there cannot be an absence
of memory on any adjacent channel.

The Flex memory setup, always does the best it can (i.e. you
can't "build a better one"). And all it needs to do that, is
for the hardware (controllers) to be set up properly, so that
a continuous physical memory map exists (i.e. don't have
two controllers respond to the same absolute address).

Note ref to "memory controllers" (plural).

Another thing you can do, is tolerate this kind of configuration.

2GB 4GB

In that case, the lower 2GB+2GB of memory space is dual channel, while
the last remaining 2GB on the right, runs single channel. This makes the
bandwidth performance of the memory, location specific. The
computer still works. (I tested this about five years ago, on
one of my computers, and couldn't detect which memory space I was
in, based on the observed speed.)
You couldn't discern a difference between single and dual-channel performance?

I don't follow you on this. If you have 2gb in channel A and 4gb in channel B:

a.) It is dual-channel unbalanced.
b.) According to the manual, the board maps 2gb from each channel as dual-
channel, and the excess 2gb in channel B as single-channel (per section 2.4.2).
I was able to use a specially modified copy of memtest86+, to verify
my memory controller actually worked that way. The dual channel section
of the memory space, ran 1400MB/sec, while the single channel section of the
memory space, ran 900MB/sec. (That gives you some idea how long ago this was.)
The memory config looked like this.

512MB --- remaining memory runs at single channel rates
512MB 512MB --- dual channel memory space

What I'm saying is, when running applications in Windows, if you're blindfolded,
you can't tell which portion of that space you're using at the moment. Even
though there is a 500MB/sec difference in memory bandwidth, the L1 and L2
cache tend to hide the details. It feels just as smooth, as if the
machine was running fully at 1400MB/sec.

Check.

The benchmark application can detect the difference, and I used memtest86+
because it works with physical memory addresses, and I could be absolutely
sure of what I was testing. The code change required adding three lines
to the source, to print additional information to the memtest screen.

Neat.

So you can do just about anything you want with it.
Subject to certain performance constraints.
Pre-built computers are frequently shipped with "stupid" configurations,
which takes advantage of Flex memory, and nobody is the wiser.

One reason why we build.

If it was mine, I'd run it like this

4GB 4GB

and save the 2x2GB in a drawer for later. If the 4GB modules fail,
you have some spare memory on hand. Or, if you decide some day to test
12GB, again, you can do it. (I prefer to run my machines with two sticks,
and have done so, on the last four computers.)

4GB 4GB
2GB 2GB
There are certain advantages in so doing. If the 4gb modules were selling
for, say, $12 each ...

Cheers,
P
So you're saying, you don't appreciate the fact you're getting a
gigabyte of memory for roughly $10 ?

Actually a bit less. $34/4 = $8.50.

How many things can you buy at the
store today, that are falling in price ? I went to Home Depot the
other day, to price a four foot length of tubular steel, and
they wanted close to $16 for it.

Yeah, it's been like that around here for years. Vicious price increases
and strictly comical gov't efforts to lie about it.

Luckily for us, memory is
still headed in the opposite direction. And it's not
even clear, why that is happening. You'd think with
Japan all messed up, there'd be some price gouging.

Most memory is made in non-Nipponese Asian locales?

For the record, I -have- to appreciate the $8.50/gb price because
I cannot forget having to pay ~ $110/4 = $27.50/gb for it 13 months
ago. There was a "spike", and I needed to complete/test a build.

But I have to justify expense on pc resources according to expectations of
usage. If the "sweet spot" for my little desktop is expected to be around 8gb
physical mem, it's hard to justify the additional expense of an added 4gb, if
only $34.

Prost,
P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."


I don't know, exactly how Intel chose to implement their memory
control. But the difference is, there is more independence between
DIMMs and channels. AMD simplified their scheme, because doing
so reduced the design time to get their product to market. Intel
has about 10x the design resources of AMD, so they can do all
sorts of stuff if they want. As far as I know, Nvidia were the
first to support this sort of thing (Flex memory like operation),
so Intel shouldn't necessarily get all the credit.

In the case of the Nforce2 chipset (the one I tested with the custom
version of memtest86+), if you looked in Device Manager, there
was actual evidence of individual entries for controllers. Intel
doesn't show such details. Which is fine, because it can all remain
safely hidden at the BIOS level. (The BIOS does all the heavy
lifting anyway, and sets up the mappings and any hardware details.
Windows shouldn't be doing that.)

When there are uneven amounts of memory on each channel, for some
amount of that memory available, it'll be possible to identify
matching amounts. For example, for the purposes of drawing a diagram,
I can install two DIMMs like this.

512MB 1GB

and it ends up looking like this, for the purposes of explanation.

512MB
512MB 512MB

For the bottom 1GB of space, you can alternate side to side, going
up through the memory space.

At just above the 1GB mark, now, you've only got 512MB remaining,
and it's on the right hand channel. There is no opportunity to
go from side to side any more. Accesses can only go to that channel,
and so the measured memory bandwidth drops. When I did my benchmark
with memtest86+, that's what I found. Above the "magic mark" for
my configuration, bandwidth changed from 1400MB/sec to 900MB/sec.

You can see here, that Flex Memory usage is detectable with synthetic
benchmarks, but is harder to see with practical applications. Notice
that the system still works in single channel, and single channel
mode has a bit more of a penalty. The problem with doing benchmarks
in this way, is you have no control over what memory is being tested.
Presumably, at least initially after a reboot, Windows "fills" memory
in a certain direction. Either choosing to start at the top of the
physical address space, or nearer the bottom. So when doing these
kinds of tests, with a memory configuration like the one I show above,
particular care would have to be used to get the "right" result. For
example, if your benchmark happened to run within the lower 1GB,
you might see no difference at all between true dual channel, and
some unbalanced flex mode.

http://www.tomshardware.com/reviews/...ch,830-28.html

This isn't a worry for you. If you want to run 2+2 on one channel and
4GB on the other channel, that is "dual channel all the way". If
you want to test how much of an effect an unbalanced config can
make, you can also test 2GB on one channel, and 4GB on the other (6GB total).
Then do your benchmarks.

Paul