understanding memory specs help

Hi.

I don't really understand memory specs.

I am considering the two sets below.

is one faster than the other?

I don't know what the pc6400 type numbers I see mean.

Are both the following 667MHz?

would I notice any difference in performance between the two.

Its just used for word, surfing, very simple excel and creating
simple powerpoint presentations.


Corsair Value Select 2048Mb (2x 1024Mb) DDR2 667 Memory
Size 2048Mb (2x 1024Mb)
Bus Speed PC-5300
CAS Latency 3.0 (ns)




Corsair TwinX 2048Mb DDR2-6400 (2x1024Mb) w/ Heat Spreaders
Size 2048MB
Bus Speed XMS2-6400 DDR2-6400
CAS Latency 5-5-5-12
Number of Pins 2 x 240 Pin
--
Nospam

Nospam wrote:

Hi.

I don't really understand memory specs.

I am considering the two sets below.

is one faster than the other?

I don't know what the pc6400 type numbers I see mean.

Are both the following 667MHz?

would I notice any difference in performance between the two.

Its just used for word, surfing, very simple excel and creating
simple powerpoint presentations.

Corsair Value Select 2048Mb (2x 1024Mb) DDR2 667 Memory
Size 2048Mb (2x 1024Mb)
Bus Speed PC-5300
CAS Latency 3.0 (ns)

Corsair TwinX 2048Mb DDR2-6400 (2x1024Mb) w/ Heat Spreaders
Size 2048MB
Bus Speed XMS2-6400 DDR2-6400
CAS Latency 5-5-5-12
Number of Pins 2 x 240 Pin
--
Nospam

One number is the millions of transfers per second, while the
other is the bandwidth in megabytes per second. The numbers
are optimistic, and assume that the memory can deliver data
on each and every cycle, but memory busses are seldom 100%
efficient.

DIMMs are 8 bytes wide. The transfer rate in one of your
examples is DDR2-667 and that gets multiplied by 8 bytes
for each transfer, to get the megabytes per second. That
gives the PC-5300 number (5300MB/sec).

One memory runs at a maximum of 667 Million transfers per
second, and the other at 800 Million.

The other difference is CAS latency. Column address strobe
latency is the time from the column address strobe, until
the first data cycle to/from the DIMM. Latency is measured
in cycles. Low latency means the processor is stalled for
less time, waiting for the data it needs to arrive. The two
memories don't have the same cycle time, and cycle time
is the inverse of the clock rate. 3 cycles at (1/667) is less
delay than 5 cycles at (1/800), relatively speaking.

Does any of this matter ? The best way to figure it out,
is via benchmarks or reviews.

http://www.anandtech.com/memory/showdoc.aspx?i=2732&p=4

Notice in the above table, that one game actually runs
slower, once you get away from DDR2-533. SuperPI improves
a bit. Far Cry improves a bit. Notice how Far Cry with
667 memory is the same speed as 533 memory. That could
even be because of some BIOS trickery (Intel datasheet
restriction on operating mode of chipset being honored
by the BIOS designer).

Many DDR2 memories are capable of being overclocked,
and trade relaxed memory timings for clock rate. Thus
your DDR2-667 CAS3 memory might be capable of running
at DDR2-800 CAS5. Reading more review articles on
Anandtech might show you more about how DDR2 behaves.

I guess you'll have to decide whether the small difference
you see in the Anandtech test results, is something you
gotta have. Instead of sinking an extra $100 or $200 or
whatever the price differential is today, you might invest
that money in a faster processor instead. A higher clock
on the processor might be worth more to you, than the
lesser improvement given by slightly faster memory.

Check your motherboard manual to make sure you can get the
value from the DDR2-800 memory. It would be pretty
disappointing to buy the DDR2-800 memory, only to find
a note in the manual that says the chipset runs at
533 or 667 only.

Paul

Thanks for that.

if I have understood this correctly!

the VALUE memory is
===================
667MHz with a bandwidth of 5300MB/sec
(8x667 MHz = 5336 = 5300 rounded-down)

so should be described on the supplier's website as

DDR2-667 PC530



the TWINX memory is
===================
800MHz with a bandwidth of 6400MB/sec
(8x800 MHz = 6400)


so should be described on the supplier's website as

DDR2-800 PC640



The motherboard I have in mind is the Asus M2N-VM DH

http://www.asus.com.tw/products4.asp...3&l1=3&l2=101&
l3=345


The memory spec says:

Dual channel memory architecture
4 x 240-pin DIMM sockets support
max. 8GB DDR2 800/ 667/ 533 non-ECC,
un-buffered memory



So I think both memory sets should work.
If I have understood things correctly.

I just have to decide is 38UKP worth spending on the faster memory.

would I notice any difference using word, powerpoint,
excel and surfing on win XP home. I guess not.


I might be better buying 4x1020 of the slower memory than 2x1024 of the
faster memory.

I will, once in a while, use the PC to edit my home movies, but most of
the time I do the editing on the DVD player. I just transfer the video
to the DVD's hard disc and edit it there.

there is the odd occasion that I will want to play with video editing
but not often, don't have the time really.


thanks for the advice.





Nospam wrote:

Hi.

I don't really understand memory specs.

I am considering the two sets below.

is one faster than the other?

I don't know what the pc6400 type numbers I see mean.

Are both the following 667MHz?

would I notice any difference in performance between the two.

Its just used for word, surfing, very simple excel and creating
simple powerpoint presentations.

Corsair Value Select 2048Mb (2x 1024Mb) DDR2 667 Memory
Size 2048Mb (2x 1024Mb)
Bus Speed PC-5300
CAS Latency 3.0 (ns)

Corsair TwinX 2048Mb DDR2-6400 (2x1024Mb) w/ Heat Spreaders
Size 2048MB
Bus Speed XMS2-6400 DDR2-6400
CAS Latency 5-5-5-12
Number of Pins 2 x 240 Pin
--
Nospam

One number is the millions of transfers per second, while the other is
the bandwidth
in megabytes per second. The numbers are optimistic, and assume that the
memory can deliver data on each and every cycle, but memory busses are
seldom
100% efficient.

DIMMs are 8 bytes wide. The transfer rate in one of your examples is
DDR2-667
and that gets multiplied by 8 bytes for each transfer, to get the
megabytes per
second. That gives the PC-5300 number (5300MB/sec).

One memory runs at a maximum of 667 Million transfers per second, and
the other
at 800 Million.

The other difference is CAS latency. Column address strobe latency is
the time
from the column address strobe, until the first data cycle to/from the
DIMM. Latency
is measured in cycles. Low latency means the processor is stalled for
less time,
waiting for the data it needs to arrive. The two memories don't have the
same cycle
time, and cycle time is the inverse of the clock rate. 3 cycles at
(1/667) is less delay
than 5 cycles at (1/800), relatively speaking.

Does any of this matter ? The best way to figure it out, is via
benchmarks or
reviews.

http://www.anandtech.com/memory/showdoc.aspx?i=2732&p=4

Notice in the above table, that one game actually runs slower, once you
get away
from DDR2-533. SuperPI improves a bit. Far Cry improves a bit. Notice
how Far
Cry with 667 memory is the same speed as 533 memory. That could even be
because of some BIOS trickery (Intel datasheet restriction on operating
mode of
chipset being honored by the BIOS designer).

Many DDR2 memories are capable of being overclocked, and trade relaxed
memory timings for clock rate. Thus your DDR2-667 CAS3 memory might be
capable of running at DDR2-800 CAS5. Reading more review articles on
Anandtech might show you more about how DDR2 behaves.

I guess you'll have to decide whether the small difference you see in
the Anandtech
test results, is something you gotta have. Instead of sinking an extra
$100 or $200
or whatever the price differential is today, you might invest that money
in a faster
processor instead. A higher clock on the processor might be worth more
to you,
than the lesser improvement given by slightly faster memory.

Check your motherboard manual to make sure you can get the value from
the
DDR2-800 memory. It would be pretty disappointing to buy the DDR2-800
memory,
only to find a note in the manual that says the chipset runs at 533 or
667 only.

Paul


Nospam wrote:

Hi.

I don't really understand memory specs.

I am considering the two sets below.

is one faster than the other?

I don't know what the pc6400 type numbers I see mean.

Are both the following 667MHz?

would I notice any difference in performance between the two.

Its just used for word, surfing, very simple excel and creating
simple powerpoint presentations.

Corsair Value Select 2048Mb (2x 1024Mb) DDR2 667 Memory
Size 2048Mb (2x 1024Mb)
Bus Speed PC-5300
CAS Latency 3.0 (ns)

Corsair TwinX 2048Mb DDR2-6400 (2x1024Mb) w/ Heat Spreaders
Size 2048MB
Bus Speed XMS2-6400 DDR2-6400
CAS Latency 5-5-5-12
Number of Pins 2 x 240 Pin
--
Nospam

One number is the millions of transfers per second, while the other is
the bandwidth
in megabytes per second. The numbers are optimistic, and assume that the
memory can deliver data on each and every cycle, but memory busses are
seldom
100% efficient.

DIMMs are 8 bytes wide. The transfer rate in one of your examples is
DDR2-667
and that gets multiplied by 8 bytes for each transfer, to get the
megabytes per
second. That gives the PC-5300 number (5300MB/sec).

One memory runs at a maximum of 667 Million transfers per second, and
the other
at 800 Million.

The other difference is CAS latency. Column address strobe latency is
the time
from the column address strobe, until the first data cycle to/from the
DIMM. Latency
is measured in cycles. Low latency means the processor is stalled for
less time,
waiting for the data it needs to arrive. The two memories don't have the
same cycle
time, and cycle time is the inverse of the clock rate. 3 cycles at
(1/667) is less delay
than 5 cycles at (1/800), relatively speaking.

Does any of this matter ? The best way to figure it out, is via
benchmarks or
reviews.

http://www.anandtech.com/memory/showdoc.aspx?i=2732&p=4

Notice in the above table, that one game actually runs slower, once you
get away
from DDR2-533. SuperPI improves a bit. Far Cry improves a bit. Notice
how Far
Cry with 667 memory is the same speed as 533 memory. That could even be
because of some BIOS trickery (Intel datasheet restriction on operating
mode of
chipset being honored by the BIOS designer).

Many DDR2 memories are capable of being overclocked, and trade relaxed
memory timings for clock rate. Thus your DDR2-667 CAS3 memory might be
capable of running at DDR2-800 CAS5. Reading more review articles on
Anandtech might show you more about how DDR2 behaves.

I guess you'll have to decide whether the small difference you see in
the Anandtech
test results, is something you gotta have. Instead of sinking an extra
$100 or $200
or whatever the price differential is today, you might invest that money
in a faster
processor instead. A higher clock on the processor might be worth more
to you,
than the lesser improvement given by slightly faster memory.

Check your motherboard manual to make sure you can get the value from
the
DDR2-800 memory. It would be pretty disappointing to buy the DDR2-800
memory,
only to find a note in the manual that says the chipset runs at 533 or
667 only.

Paul

--
Nospam