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Regarding the CPU & RAM bus speed

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October 26, 2007 6:24:53 PM

Hi all,

I am in the process of building a new PC (not for games purposes, just some multimedia and internet tasks), and I have a silly doubt regarding the processor+chipset+RAM memory combination.
Right, the stuff that I have chosen is:

- Motherboard with chipset Intel G33 Express, with system bus running at 1333/1066/800 MHz

- Processor: Intel Core 2 Duo E6750 with with system bus running at 1333 MHz

- RAM Memory: 4 GB (2 set of 2 GB) at... 800 MHz??

Ok, and this is my doubt: as far as I know, and in order to avoid potential bottlenecks, both the CPU and the RAM should be working at the same bus speed, that is 1333 MHz ((pls correct if I am wrong).
The thing is that the RAM at 1333 (DDR3) is extremely expensive (at least here in Spain). But the curious thing is that in almost all the reviews and CPUs comparatives that I have checked (including the test in Tom's Hardware), almost all the systems that include Intel Core 2 Duo processors are configured with DDR2 memory at 800 MHz... is there or not potential risk of bottleneck because the CPU and RAM running at different speed?... Am I missing something?... :??: 

Thanks all for your help.

PS: apologies for my poor English :ange:  .

More about : cpu ram bus speed

October 26, 2007 6:37:50 PM

A lot of people get confused by this so don't worry. CPU's run quad pumped which means they send info 4 times per clock so a CPU with a 1333FSB is actually running at 333x4. DDR (Double Data Rate) RAM sends info twice per clock so in order to run 1:1 with your 1333FSB you would need DDR2 667 which when run in dual-channel is running at 1333. The reason most opt for DDR2 800 or higher is for overclocking because with RAM that speed you can run your CPU up to 1600FSB before you need to start overclocking the RAM.

Take my setup for instance, I have a E6300 overclocked to 1600FSB and DDR2 800 running 1:1 with the CPU. For you I would just look for inexpensive, quality DDR2 667 RAM.

I know your not from the US but just to give you an idea what to look for this http://www.newegg.com/Product/Product.aspx?Item=N82E168... is a great product and very inexpensive after rebate

and this http://www.newegg.com/Product/Product.aspx?Item=N82E168... is another one which is good and has slightly better latency.
October 26, 2007 6:46:23 PM

Don't buy DDR3 RAM (Unless your motherboard absolutely can't handle anything else). DDR2 is just as good w/o the hefty price tag. Just buy some PC6400 or DDR2 800 (as stated above) and you'll be fine.
Related resources
October 26, 2007 9:16:44 PM

400fsb cpu 200fsb memory

works great i run one just like it! i think its 3.4ghz?

this is a 1:1 ratio so there is no latency - some call it a 2:1 but cpuz shows 1:1

the main thing is you want the memory to be half the cpu - true 1:1 is hard to achieve and provides little performance gains and most cases you pay more for less.

for example a stock 1066 chip with 1066 ran has a lower bandwidth due to the 5-5-5-15 latencys then the second example below:

2nd example:

so if you have 3.37 (1.41-1.42v at full load) ghz e6600 at 1500fsb you run you memory at 750mhz and lower the latency's - maybe

4-4-3-8 ran at 750mhz runs great stock - super-talent at $80 you get a memory bandwidth of 6800-7200 @2.05-2.1v

i use this example since i build these all the time!
October 26, 2007 9:39:40 PM

i checked my systems
6750/g33 in silverstone microatx box 2 raptors in raid0 250gb storage and game drive.

memory cooler and chip set fan added to the gigybyte mobo - asus are better and much easier to oc. but this mobo seems more stable with vista issues.

my cpu is 3.4ghz 425fsb memory is 850mhz
the ram is mushkin 4-4-3-10 at 2.1v 5-5-4-14
Vfsb is max Vcore 1.4375
October 26, 2007 10:26:22 PM

ausch30 said:
A lot of people get confused by this so don't worry. CPU's run quad pumped which means they send info 4 times per clock so a CPU with a 1333FSB is actually running at 333x4. DDR (Double Data Rate) RAM sends info twice per clock so in order to run 1:1 with your 1333FSB you would need DDR2 667 which when run in dual-channel is running at 1333. The reason most opt for DDR2 800 or higher is for overclocking because with RAM that speed you can run your CPU up to 1600FSB before you need to start overclocking the RAM.

Take my setup for instance, I have a E6300 overclocked to 1600FSB and DDR2 800 running 1:1 with the CPU. For you I would just look for inexpensive, quality DDR2 667 RAM.

I know your not from the US but just to give you an idea what to look for this http://www.newegg.com/Product/Product.aspx?Item=N82E168... is a great product and very inexpensive after rebate

and this http://www.newegg.com/Product/Product.aspx?Item=N82E168... is another one which is good and has slightly better latency.


Wow, AUsch30... thank you very much for clarifying this... now it makes sense to me...
I think that, given that I will hardly ever try to overclock the system, I will go for the DDR2 667 RAM.
Again, thank all for your ideas...

Regards.


October 26, 2007 10:37:20 PM

Quote:
If you're still confused by the excellent advice above,
here's how to simplify these concepts:

On Intel systems ...
800 means one thing for the Front Side Bus and
800 means a different thing for the memory bus
because the Northbridge has 2 busses:
one to the CPU and one to the RAM.

Let's start with RAM:

DDR2-800 means an effective clock rate of 800 Mhz;
but, the "frequency" of the RAM clock is only 400 MHz,
because "DDR" means Double Data Rate: data is transmitted
twice for every tick of that memory bus clock.


And now for the CPU:

A rated FSB of 800 MHz means a raw bus speed of 200 MHz,
because the Front Side Bus sends data 4 times for every tick
of that CPU bus clock. That's just the way that Intel chipsets
and Intel CPUs are designed to operate together.

Thus, our workstations here have a very common setup:
200 MHz "Bus Bpeed" x 4 = 800 MHz "Rated FSB" and
400 MHz "DRAM frequency" x 2 = DDR2-800 .

And, because 16 bytes are transmitted for every raw tick
of the DRAM clock, or 8 bytes transmitted for each effective
tick of the memory bus, 400 x 16 = DDR2-800 x 8 bytes = 6,400 MB/sec.


Thus, the memory bandwidth of our common systems is 6.4 GB/second
(i.e. 6,400 megabytes per second).

That is why DDR2-800 is also known as PC2-6400 i.e. 6400 MB/second.


If you download and install CPU-Z, you can standardize
on the measurements it reports: on the above setup
the "Bus Speed" is reported to be 200 MHz and
the "DRAM Frequency" is reported to be 400 MHz,
for an FSB:D RAM ratio of 1:2.

Some folks like to refer to 800:800 as "1:1", but
that computation conflicts with the convention
used by the CPU-Z software.

It is highly recommended that we standardize on the
terminology reported by CPU-Z, because that
software is in such widespread use.


I hope this helps.


Sincerely yours,
/s/ Paul Andrew Mitchell
Webmaster, Supreme Law Library
http://www.supremelaw.org/


supremelaw, thank you for the explanation... I have installed CPU-Z in my old system, and I am happy to say that both the CPU and the memory are running at the same frequency... and what is more important: now I know WHY and HOW this is possible... :bounce: 

Thanks all again.
it's great to find such a helpful folks like you guys.


October 26, 2007 11:01:03 PM

yeah there's 0 problems ram is the last thing to worry about when it comes to bottlenecking
!