Front Side Bus bandwidth matching memory bandwidth...

Hi...thanks to read.

I wish to build a new computer based on the ASUS P5LD2. The cpu that will be
installed will run on 800MHz FSB. Yet, i've read that the memory bandwidth,
as much as possible, must match the fsb bandwidth. The maximum DDR2 speed
that the P5LD2 accepts is 667MHz. It is a waste to install more that two
DDR2 400MHz in dual-channel, considering that the theorical bandwidth of
those modules together is 6400MB/sec wich is the bandwith of the 800MHz fsb?
In the mean time i'm still googling to get more info. T IA for your reply.


--
Alain(alias:Kilowatt)
Montréal Québec
PS: 1000 excuses for grammatical errors or
omissions, i'm a "pure" french canadian! :-)
(If replying also by e-mail, remove
"no spam" from the adress.)

KILOWATT wrote:
> Hi...thanks to read.
>
> I wish to build a new computer based on the ASUS P5LD2. The cpu that will be
> installed will run on 800MHz FSB. Yet, i've read that the memory bandwidth,
> as much as possible, must match the fsb bandwidth. The maximum DDR2 speed
> that the P5LD2 accepts is 667MHz. It is a waste to install more that two
> DDR2 400MHz in dual-channel, considering that the theorical bandwidth of
> those modules together is 6400MB/sec wich is the bandwith of the 800MHz fsb?
> In the mean time i'm still googling to get more info. T IA for your reply.
>
DDR 400 is the way to go for that processor.

In article <44d3dc74$0$8105$c3e8da3@news.astraweb.com>, "KILOWATT"
<kilowatt"nospam"@softhome.net> wrote:

> Hi...thanks to read.
>
> I wish to build a new computer based on the ASUS P5LD2. The cpu that will be
> installed will run on 800MHz FSB. Yet, i've read that the memory bandwidth,
> as much as possible, must match the fsb bandwidth. The maximum DDR2 speed
> that the P5LD2 accepts is 667MHz. It is a waste to install more that two
> DDR2 400MHz in dual-channel, considering that the theorical bandwidth of
> those modules together is 6400MB/sec wich is the bandwith of the 800MHz fsb?
> In the mean time i'm still googling to get more info. T IA for your reply.
>
>
> --
> Alain(alias:Kilowatt)
> Montréal Québec
> PS: 1000 excuses for grammatical errors or
> omissions, i'm a "pure" french canadian! :-)
> (If replying also by e-mail, remove
> "no spam" from the adress.)

This chart is produced with a FSB1066 processor. Using two sticks
of DDR2-533 RAM (4264MB/sec) would match the 8528MB/sec of the
processor FSB. But you notice in the chart, that while the step
from DDR2-400 to DDR2-533 is a significant one, you still get
a slight boost from using RAM a step or two faster.

http://www.anandtech.com/showdoc.aspx?i=2729&p=4

The reason for this, is the memory bus is not kept 100% busy, and
while the memory in my example above is good for 4264MB/sec,
some of the cycles on the bus, carry no read or write data.
By increasing the clock rate a bit more, it is possible to
compensate for this less than 100% efficient memory interface.

I would say DDR2-533 would be your best value, and DDR2-667
would buy you a tiny bit more. At those lower speeds, you
may be able to find some CAS3 memory to use, and the lower
the latency (if it is reasonably priced), the better off
you would be.

If you buy DDR2-400 memory, you would never be able to
resell it later on Ebay :-)

Paul

Thanks a lot for the replies. Yes Paul, from the chart on the page you've
linked, and a few other place i've visited, it seems that DDR 667 scores a
little more even if not dramatically. The price is the same at Microbytes
here in Montréal for 400 or 667MHz for many module's capacity. It's only on
800 and 1000MHz modules (yet) that the price then start to
climb...dramatically!


--
Alain(alias:Kilowatt)
Montréal Québec
PS: 1000 excuses for grammatical errors or
omissions, i'm a "pure" french canadian! :-)
(If replying also by e-mail, remove
"no spam" from the adress.)