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Clock doubts

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August 23, 2010 3:22:09 PM

There are some questions that I can't quite a hold of !

I have a Dell laptop(Intel) and an Amd based desktop.

1.Does the fsb always govern the frequency of all other components (ram,cpu,ht)?

2.In DDR3 is the dram frequency always 4x the fsb, (fsb:D ram ratio)?

3.My dell laptop Ram (1333Mhz) operates at 1066 Mhz, the fsb is given as 133Mhz in cpuz, is that the reason ?

4. In cpuz first page a value suggests that it is the bus frequency,is it the fsb frequency ?

5.If my fsb is 133, my dram should be 133*4 ie 532 and the transfer rate 1064, insted it shows up as 533 and 1066, how ?

Whenever I change my so called bus frequency in the Bios of the desktop all other components have their clocks upped by some value.

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a c 197 K Overclocking
August 23, 2010 6:22:37 PM
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Definition time (attention purists, I'm talking about DDR2 and I'm simplifying a little :) ):
Core2 CPU's use a frontside bus (FSB). The FSB is a thing with two main characteristics: speed which is usually defined in MHz and width which in the Core2's is 64 bits wide. We are concerned with the speed.

Using the Q6600 as an example, the FSB frequency is 266 MHz. The matching DDR2 memory clock for that frequency is 533 MHz (266 X 2). DDR2 memory transfers two chunks of data for each bus cycle, hence double the frequency. So, to run 1:1 at an FSB of 266 MHz, we need DDR2-533 RAM. What CPUZ does is a little confusing. It will tell you that the memory frequency is 266 MHz for a 1:1 ratio.

The FSB clock is 1066 MHz (266 X 4). The bus is "quad pumped". It transfers 4 chunks of data into and out of the CPU each cycle. So each FSB cycle generates 4 FSB clocks.

Now, if you increase the FSB frequency to 333 MHz, the corresponding memory clock is 667 MHz and the FSB clock is 1333 MHz.

Old definitions. :)  For DDR3 RAM, each bus cycle generates 4 memory clocks instead of 2. And notice the distinction between "frequency" and "clock".

#1. Sort of.

#2. In DDR3, the dram frequency always equal to the fsb frequency, (fsb:ram ratio). In DDR3, the dram clock is equal to the fsb frequency.

#3. Don't know. I am still using Core2 systems with DDR2 RAM.

#4. Yes.

#5. Technically, the fsb frequency is supposed to be 133.3 MHz.
a c 100 K Overclocking
August 23, 2010 6:39:38 PM

What core is in the laptop? Sounds to me like maybe the i core series... 133x8=1064 which is a valid RAM multiplier... These mobos (P55, X58) use a base clock instead of FSB, and then you have multipliers (CPU, RAM, QPI). Ram can be 6x, 8x, 10x so it makes sense if you're using this series and by default it is set to 8x (although, that is a bit odd).

Either way, you should go into the BIOS and check if you can get all your components running at their rated speeds. For RAM, you can usually go to the manufacturer's site to get their rated speed, timings, and voltage.
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August 24, 2010 5:01:22 AM

Im using a dell Inspiron 15r with core i5 cpu, while purchasing the website had suggested that the memory runs at 1066mhz because the cpu limits it.


Also , my reason for confusion is mainly the wikipedia article which shows different memory clock form different modules !

http://en.wikipedia.org/wiki/Ddr3#JEDEC_standard_module...

The second column.

Also at the top of the page they've mentioned how ddr3 frequency is calculated. In that what is the memory clock and bus clock rate?

What follows can be understood.

Does the fsb vary for each cpu design ?


Thanks,btw !
August 24, 2010 7:48:14 AM

Best answer selected by virajk.
a c 100 K Overclocking
August 24, 2010 2:54:51 PM

Like I said, i5 does not have a front side bus. It has a base clock and multipliers. The base clock does change a little bit depending on CPU, yes. It's usually 133 but it could be different. I'm pretty sure you can go into your BIOS and get the RAM running at 1333.
August 24, 2010 3:08:54 PM

Unfortunately there is no such options in the dell BIOS of my laptop.
However when you mentioned the base clock is used is it the same one that plays a role in fsb:D ram?
a c 100 K Overclocking
August 24, 2010 4:48:37 PM

It's similar, yes, but Intel revamped the whole system. No more FSB, and they have Quick Path Interconnect that takes care of the CPU, PCIe, and RAM links, as well as a DMI (forgot what this acronym means) to connect to the south bridge. QPI is a lot better/faster than FSB. And it's handled via base clock and multipliers... but how you work with them is quite similar.

I checked it out, you probably have the i5 540M. This mobile CPU supports 1066mhz, so looks like there is a hardware limitation. I would have to think, then, if you set your base clock up to 166 you could get the RAM at 1333 but I don't know if OCing is even possible on a Dell laptop. Looks like your computer is running fine tho.
August 24, 2010 6:18:46 PM

That clears most of my doubts.No need to bother now that the fsb concept is gone !

Thanks !
!