DDR2 vs. Dual Channel DDR2

[Richard in Va.]

A basic memory question, what's the difference between...

PC4200 DDR2 533MHz & Dual Channel PC4200 DDR2 533MHz Memory?

PC = Dell OptiPlex GX620 Mid Tower. The Dell manual recommends "Dual Channel
DDR2" installed in matched pairs, but I think my "used" PC's came with
"single channel" ram installed. The Dell specs state that 533MHz (or)
677MHz memory is supported.

The tigerdirect.com memory configurator shows std DDR2 & Dual Channel DDR2
for my OptiPlex GX620, but all as 533MHz. One of their customer reviews
said they installed a Dual channel 533MHz memory configuration and his BIOS
auto clocked the memory to 677MHz. I have no idea if he's using a Dell PC.

So, basic question is... what's the basic difference between PC4200 DDR2 &
Dual Channel PC4200 DDR2 ?

Also, would it be true that if I install Dual Channel RAM and insure they
are in matched memory size pairs, that the BIOS will auto-clock the 533MHz
RAM to 677MHz?

Thanks for any "heads up" on this

Happy New Year!

Richard in Va.
++++++++++++

 

[Paul]

A basic memory question, what's the difference between...

PC4200 DDR2 533MHz & Dual Channel PC4200 DDR2 533MHz Memory?

PC = Dell OptiPlex GX620 Mid Tower. The Dell manual recommends "Dual Channel
DDR2" installed in matched pairs, but I think my "used" PC's came with
"single channel" ram installed. The Dell specs state that 533MHz (or)
677MHz memory is supported.

The tigerdirect.com memory configurator shows std DDR2 & Dual Channel DDR2
for my OptiPlex GX620, but all as 533MHz. One of their customer reviews
said they installed a Dual channel 533MHz memory configuration and his BIOS
auto clocked the memory to 677MHz. I have no idea if he's using a Dell PC.

So, basic question is... what's the basic difference between PC4200 DDR2 &
Dual Channel PC4200 DDR2 ?

Also, would it be true that if I install Dual Channel RAM and insure they
are in matched memory size pairs, that the BIOS will auto-clock the 533MHz
RAM to 677MHz?

Thanks for any "heads up" on this

Happy New Year!

Richard in Va.
++++++++++++

First off, the memory chips don't know anything about that "dual channel"
name. They're just memory chips. If you grab a stick of RAM, and install
it in either a single channel or a dual channel motherboard, to the
memory stick its all the same. It is not like the chips themselves receive
any special treatment (they don't come off a separate production line or
anything like that).

The purpose of the "dual channel" name, when it appears on a package
of RAM, is to signify that the two sticks have matching characteristics.

If you purchase sticks of RAM individually, there is no guarantee they
are the same. For example, Kingston may purchase memory sticks from
three different contract manufacturers, and the SPD chip on the DIMMs
could have slightly different contents. It is for those reasons,
that "dual channel" products exist. The idea is, the contract company
making them, pays a little attention to nominal matching of the sticks,
so that things like the SPD (serial presence detect) EEPROM data is the
same on them.

From the motherboard end, the difference between dual channel and single
channel operation, is extra memory bandwidth. If the FSB is not a bottleneck,
then running in dual channel mode can enhance the transfer rate to the
processor. This is useful for things like WinRAR or Photoshop, which are
memory hungry. Those applications are more dependent on the performance
of the memory bus, because the processor cache may not be able to hold
everything needed. For many other applications, the difference between
the two modes of operation would be less apparent. Based on some testing
here, I have noticed that if you use the integrated graphics on the
chipset (rather than a separate video card), that dual channel memory
can make the desktop updates a little more snappy. I was able to tell,
on an 865G computer, that dual channel memory was present or not
present, simply by observing graphics updates on the screen.

Dell memory installation instructions
http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/memory00.htm

Dell chipset specs - Intel 945 (I assume they mean 945G).
http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/mtspecs0.htm#wp1133451

Intel 945 datasheet. Memory popularion rules are on page 228.
For dual channel operation, the total quantity of memory on each
channel should match. That means you could have 2x512MB on one
channel and a single 1GB stick on the other channel. That means
strict matching is not essential, as far as Intel is concerned.
But for peace of mind, and considering there is virtually no
price penalty when buying two sticks of RAM in one package,
you might as well buy a matched set. If you ever need to sell
them, it would be easier to sell a matched set, than two
orphans. (Of course, with the current low price of memory,
I don't know what you'd get for them.)

http://www.intel.com/Assets/PDF/datasheet/307502.pdf

As for the choice of operation at 533 or 667, that would
depend on the FSB and the available memory dividers. If
all the memory is rated 667, and the clock divider is available
to generate that clock, then you could get operation at
667. In some cases, some manual intervention from the user
is required. With an HP/Dell/Gateway BIOS, you never know
whether the settings you need, are going to be there.
If everything is "full auto", the BIOS can make any choice
it wants, even if you don't like it.

Paul

 

[Richard in Va.]

Hello Paul,

Wow, ask and thou shall receive... thanks for the good information... I did
not know most of that!
The Dell specs for the OptiPlex GX620 mid tower suggest 533MHz and 677MHz
DDR2 are supported.

http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/mtspecs0.htm#wp1133451

Yes I am using the on-board graphics chip, for now anyway. Everest Home
Edition shows the chipset as Intel Lakeport-G i945G. The memory page you
pointed out in the Dell manual...

http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/memory00.htm

Talks about Duel Channel and that if not used, there may be some performance
loss. One thing I didn't know is, a loss from what starting point, 677 or
533. Maybe what I should do is order some Dual Channel memory and see what
the BIOS does with it. I'll need to decide if I should try Dual Channel
PC4200 (533MHz) or Dual Channel PC5400 (677MHz). As you suggest, at today's
$$, there is not a lot to argue about... maybe get a set of each to see what
the BIOS does. I bought (3) of these PC's thru eBay and they are all
GX620's with 1GB ram on each. Maybe a test before I top-off all three.

I was stumped as to why tigerdirect.com (memory configurator) only offers
533MHz PC4200 for my GX620. Maybe their configurator doesn't realize the
Dell specs accurately.

http://memoryselector.cnetchannel.com/tigerdirect/results.asp?d4iAl600e10AAD
(the mid tower has 4 DIMM's btw)

The Dell BIOS (A11) shows the memory as... Memory Channel Mode = Dual
Interleaved, Memory Organization = x8 at 533MHz
Does this mean it's already operating as Dual channel? Weird, I bought (1)
PC4200 1Gig stick to add to the 1Gig installed by the eBay seller.

Kind of weird, Everest shows that the DIMM-1 chip is running at 533MHz and
the DIMM-2 I added is running at 677MHz (??) Below is the Everest SPD
report...

[ DIMM1: Samsung M3 78T2953CZ3-CD5 ]

Memory Module Properties:
Module Name Samsung M3
78T2953CZ3-CD5
Serial Number 5006F7DCh
Module Size 1024 MB (2 ranks, 4
banks)
Module Type Unbuffered
Memory Type DDR2 SDRAM
Memory Speed DDR2-533 (266 MHz)
Module Width 64 bit
Module Voltage SSTL 1.8
Error Detection Method None
Refresh Rate Reduced (7.8 us),
Self-Refresh

Memory Timings:
@ 266 MHz 5.0-4-4-11
(CL-RCD-RP-RAS)
@ 266 MHz 4.0-4-4-11
(CL-RCD-RP-RAS)
@ 200 MHz 3.0-3-3-8
(CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Supported
Precharge All Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Not Supported
Redundant Row Address Not Supported

[ DIMM3: PDP Systems PSD21G6672 ]

Memory Module Properties:
Module Name PDP Systems
PSD21G6672
Serial Number 27B90832h
Module Size 1024 MB (2 ranks, 4
banks)
Module Type Unbuffered
Memory Type DDR2 SDRAM
Memory Speed DDR2-667 (333 MHz)
Module Width 64 bit
Module Voltage SSTL 1.8
Error Detection Method None
Refresh Rate Reduced (7.8 us),
Self-Refresh

Memory Timings:
@ 333 MHz 5.0-5-5-15
(CL-RCD-RP-RAS)
@ 266 MHz 4.0-4-4-12
(CL-RCD-RP-RAS)
@ 200 MHz 3.0-3-3-9
(CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Not Supported
Redundant Row Address Not Supported

Got any ideas on this? I bought several 1GB single sticks, maybe I can
replace the oem one with one I bought... maybe, maybe, maybe they'll match
up?


Again, thanks for the good help!

Richard in Va.
++++++++++++

 

[Paul]

Hello Paul,

Wow, ask and thou shall receive... thanks for the good information... I did
not know most of that!
The Dell specs for the OptiPlex GX620 mid tower suggest 533MHz and 677MHz
DDR2 are supported.

http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/mtspecs0.htm#wp1133451

Yes I am using the on-board graphics chip, for now anyway. Everest Home
Edition shows the chipset as Intel Lakeport-G i945G. The memory page you
pointed out in the Dell manual...

http://support.dell.com/support/edocs/systems/opgx620/en/ug/A02/memory00.htm

Talks about Duel Channel and that if not used, there may be some performance
loss. One thing I didn't know is, a loss from what starting point, 677 or
533. Maybe what I should do is order some Dual Channel memory and see what
the BIOS does with it. I'll need to decide if I should try Dual Channel
PC4200 (533MHz) or Dual Channel PC5400 (677MHz). As you suggest, at today's
$$, there is not a lot to argue about... maybe get a set of each to see what
the BIOS does. I bought (3) of these PC's thru eBay and they are all
GX620's with 1GB ram on each. Maybe a test before I top-off all three.

I was stumped as to why tigerdirect.com (memory configurator) only offers
533MHz PC4200 for my GX620. Maybe their configurator doesn't realize the
Dell specs accurately.

http://memoryselector.cnetchannel.com/tigerdirect/results.asp?d4iAl600e10AAD
(the mid tower has 4 DIMM's btw)

The Dell BIOS (A11) shows the memory as... Memory Channel Mode = Dual
Interleaved, Memory Organization = x8 at 533MHz
Does this mean it's already operating as Dual channel? Weird, I bought (1)
PC4200 1Gig stick to add to the 1Gig installed by the eBay seller.

Kind of weird, Everest shows that the DIMM-1 chip is running at 533MHz and
the DIMM-2 I added is running at 677MHz (??) Below is the Everest SPD
report...

[ DIMM1: Samsung M3 78T2953CZ3-CD5 ]

Memory Module Properties:
Module Name Samsung M3
78T2953CZ3-CD5
Serial Number 5006F7DCh
Module Size 1024 MB (2 ranks, 4
banks)
Module Type Unbuffered
Memory Type DDR2 SDRAM
Memory Speed DDR2-533 (266 MHz)
Module Width 64 bit
Module Voltage SSTL 1.8
Error Detection Method None
Refresh Rate Reduced (7.8 us),
Self-Refresh

Memory Timings:
@ 266 MHz 5.0-4-4-11
(CL-RCD-RP-RAS)
@ 266 MHz 4.0-4-4-11
(CL-RCD-RP-RAS)
@ 200 MHz 3.0-3-3-8
(CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Supported
Precharge All Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Not Supported
Redundant Row Address Not Supported

[ DIMM3: PDP Systems PSD21G6672 ]

Memory Module Properties:
Module Name PDP Systems
PSD21G6672
Serial Number 27B90832h
Module Size 1024 MB (2 ranks, 4
banks)
Module Type Unbuffered
Memory Type DDR2 SDRAM
Memory Speed DDR2-667 (333 MHz)
Module Width 64 bit
Module Voltage SSTL 1.8
Error Detection Method None
Refresh Rate Reduced (7.8 us),
Self-Refresh

Memory Timings:
@ 333 MHz 5.0-5-5-15
(CL-RCD-RP-RAS)
@ 266 MHz 4.0-4-4-12
(CL-RCD-RP-RAS)
@ 200 MHz 3.0-3-3-9
(CL-RCD-RP-RAS)

Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Not Supported
Redundant Row Address Not Supported

Got any ideas on this? I bought several 1GB single sticks, maybe I can
replace the oem one with one I bought... maybe, maybe, maybe they'll match
up?


Again, thanks for the good help!

Richard in Va.

The two tables you just posted, are what the DIMMs are "advertising"
to the BIOS. The information is stored inside the SPD chip (maybe a
five or eight pin device soldered to the DIMM). The memories actually
all operate with the same conditions.

The BIOS picks a set of conditions, that both SPD tables can support.
If you bought a DDR2-533 stick and a DDR2-667 stick, they were both
1GB, then the BIOS could run them dual channel at DDR2-533. That is
because the faster stick, can run at a slower speed when needed. The
slowest stick determine what happens.

You'd need a copy of CPUZ from cpuid.com, to see what the current
selection is by the BIOS.

The "Dual Interleaved" could be telling you it is already in
dual channel mode.

In the following example, installing the matched DIMMs in
slot1/slot3 is dual channel. Installing the DIMMs in
slot1/slot2 would be single channel. Installing a set of
DIMMs, such that the total memory on one channel is not
equal to the other channel, causes the whole mess to
run as one virtual single channel. For example, if slot
1 and slot 2 had 256MB+512MB, and slot 3 and slot 4
had 1GB+2GB, the result would be 3.75GB running in
virtual single channel mode. In that case, no more
than one stick is accessed at a time.

slot 1 slot 2
| |
---+-------------+----------- channel

---+-------------+----------- channel
| |
slot 3 slot 4

Your chipset is missing one Intel memory controller feature
called Flex Memory. If that feature was present, then the
256MB+512MB+1GB+2GB case I just described, would have run
(partially) in dual channel mode. A total of 2*(256+512)=1.5GB
of memory would be dual channel, while the other 2.25GB would
remain as single channel. But glancing at the datasheet, doesn't
show Flex Memory mode as an option. Still, the chipset has
sufficient options with today's cheap memory, to give a
good performing solution. There isn't much incentive to
run 256MB+512MB+1GB+2GB when matched pairs are cheap even
new.

Memory pricing is so bad now, that memory manufacturers
lose money on each DDR2 stick sold. Even with the profits they
can get from DDR3, it isn't enough. When the industry
collapses, you're going to be pretty happy you stocked
up on memory today. It all depends on which governments
are in for a bailout, as to how the price shoot up.

(Example of a site that tracks the spot price.)
http://www.dramexchange.com/

Paul