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PC2700 needed in Centrino system @ 100MHz FSB?

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June 17, 2004 11:24:32 AM

Hi,
I've just bought a centrino 1.6 laptop. it has 2*256 MB PC2700 RAM, I'm going to swap those hopefully with 2*512.

I used CPU-Z and it reports the system running at 100 FSB but 400 bus speed. I don't quite understand that but, would it work just as well with PC2100 which supports 133FSB.

Maybe you enthusiasts inthe know could clarify things a bit.

Thanks.

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The bigger I am, the harder they fall.
June 17, 2004 2:17:43 PM

OK, I will clarify things.

FSB speed and memory speed are 2 different things. Your CPU talk to the chipset north-bridge via a quad-pumped FSB (100x4=400) and the chipset north-bridge talk to the memory via another bus that can run at the same speed (in case of DDR, it would be 100x2) or it can run at different speed too.

It's a simple explanation. But what's is important for you is to get memory that is compatible with your chipset. Usually any DDR will memory will work in a laptop. The only thing that can happens is if the chipset don't natively support high-speed DDR module, it will downclock it to 133MHz/100MHz. Good laptop memory SPD (SPD is a chip that contain timing and speed information of the memory module, it's located on the memory PCB) have timings for low speed usage. This means that if you buy PC2700 modules, they surely have programmed timings for 100/133/166MHz operation.

If the price difference is not much get the fastest module your laptop chipset supports. If the price difference is big, using PC2100 in laptop is usually enough since most laptop comes with 100/133FSB and 100/133 memory speed support.

NOTE : If battery life is important for you. Getting lower speed memory will increase a bit the time your laptop will run on battery. Lower speed memory use less power (not a big difference, but it's good to know this).

By the way, I just upgrade my laptop memory with a generic memory module I bought from <A HREF="http://www.memoryx.net/" target="_new">MemoryX</A>. The price was good and they shipped the module the same day I bought it from their web site. I live in Canada, I received it less than 3 weeks (via USPS - the cheapest delivery).

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It's tricky to use words like <b><font color=green>AMD</font color=green></b> or <b><font color=blue>Intel</font color=blue></b> in a signature some users could think your are biased.
June 17, 2004 4:02:52 PM

Thanks for that, it's helped a little.

So my next question is if I put 2 * 512 pc2100 will my fsb still be 100 and bus speed still be 400?

Thanks.

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The bigger I am, the harder they fall.
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June 17, 2004 4:06:08 PM

The FSB will not change FSB speed is independant of memory speed. Your CPU FSB speed will remain the same, unless you force it to another value in the BIOS. But, in most laptop it's impossible to do it. So, the FSB is fixed based on CPU identification and chipset capabilities.

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It's tricky to use words like <b><font color=green>AMD</font color=green></b> or <b><font color=blue>Intel</font color=blue></b> in a signature some users could think your are biased.
June 17, 2004 5:05:20 PM

So for my laptop which I have briefly described, PC2100 and PC2700 are no different in terms of performance?

At the moment there's not much difference in price anyway.

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The bigger I am, the harder they fall.
June 17, 2004 5:08:37 PM

Get the PC2700 if there is no much difference in price. And check your laptop manual to see if it support PC2700. If not, your PC2700 will be detected as PC2100 and everything will works fine.

In the future, if you gat another laptop, you might be able to carry the memory modules and they will run at PC2700 (assuming the laptop supports it).

--
It's tricky to use words like <b><font color=green>AMD</font color=green></b> or <b><font color=blue>Intel</font color=blue></b> in a signature some users could think your are biased.
June 17, 2004 6:21:47 PM

Yes my laptop supports pc2700. Thanks for that.

OK well once I have the new RAM I will be looking at how I can overclock. :) 

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The bigger I am, the harder they fall.
June 17, 2004 6:25:03 PM

Quote:
OK well once I have the new RAM I will be looking at how I can overclock. :) 

Overclocking a laptop is much harder than overclocking a desktop computers. Most loptop BIOS don't have overclocking options/settings. If you have an nVidia/ATI GPU in it, it can be overclocked with "coolbits" or 3rd-party tools.

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It's tricky to use words like <b><font color=green>AMD</font color=green></b> or <b><font color=blue>Intel</font color=blue></b> in a signature some users could think your are biased.
June 17, 2004 7:01:47 PM

Imagine how hot it would be!!! Also Overclocking would probably mean raising voltages, which means shorter battery life. I'm not sure if it'd really be worth it. Exspecially since it is probably a pretty expensive laptop would you really want to risk permanant damage to it for just a couple hz?

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a b V Motherboard
June 18, 2004 4:33:57 AM

Your laptop processors has a 100MHz CPU bus speed (measured in clock cycles) that's also 400MHz data rate. The data rate is 4x the clock rate because Quad Data Rate technology does 4 transfers per clock cycle rather than one.

I'm fairly certain your chipset can't do dual-channel RAM addressing. Therefor, the optimal memory (having the same bandwidth as the CPU) would be DDR400 (Double Data Rate). But your chipset probably doesn't support that, so PC2700 (DDR333) is your next choice down. PC2100 would create an even larger bandwidth differential between the memory bus and CPU bus, so PC2700 would be recommended.

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June 18, 2004 9:00:10 AM

OK thanks for the tips peeps. With regards to overclocking and risking damaging an expensive piece of equipment well, I don't want to increase the multiplier so definitely won't need to increas the voltage. I just want to see how much I can safely take this laptop up to.

It's currently a 1.6 GHz Pentium-M (Centrino) with 2*256 MB PC2700 RAM.
It's running at 100 FSB and the resulting bus speed is 400 MHz.

Each MHz I add to the fsb I'll get 4MHz bus speed overall. The way I understood it was that if it's running at 100MHz fsb and PC2700 can handle 166MHz FSB and more when you overclock, then I thought I might be able to get from 100 to 133 so a resulting 533 MHz bus speed.

Is my understanding right or am I gonna blow my laptop up?

I understand all the implications it will have, with regards to battery life etc. At the moment I know that the BIOS does not give me any overclocking options, but there must be a software solution like softFSB that I can use, I just have to identify my PLL/IC.

Anyway I'm looking forward to your comments, ideas and clarifications.

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The bigger I am, the harder they fall.
a b V Motherboard
June 18, 2004 9:18:41 AM

No, each MHz you add to the FSB will add 16MHz to your CPU clock speed.

Multipliers work based on real clock rate, not data rate conversions using QDR numbers. Your CPU runs at 16x100MHz.

And your RAM is already running at 166MHz. It's split at the northbridge. The CPU bus is running at 100MHz clock rate, the RAM at 166MHz clock rate. The Memory Controller is capable of running a ratio, in this case 5:3, that is your RAM gets 5 clocks for every 3 clocks of your CPU bus.

This is probably a good thing for you, because the CPU had a data rate of 4x its bus speed, but the RAM only has a data rate of 2x its bus speed. So your data rates are 400MHz for the CPU, 333MHz for the RAM, and the RAM is still the slower bandwith part even though it's clocked higher.

It's unlikely that SoftFSB will have the PLL entry for your board, it's too new. But there's always the slim chance your board is using an older PLL. Not likely given the way it has to devide your bus speeds.

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June 18, 2004 10:17:20 AM

Thank you for the detailed and informative explanation.

OK I'' look into getting PC3200 RAM. I'm guessing, because of the mobo settings, even if I stick the PC3200 RAM in I won't get an automatic boost I don't think.

What is the easiest way for me to go about FSB overclocking this laptop, even if it's just a few MHz, I would like to push this baby to BSOD just to see how far it'll go then I can ease up.

Cheers.

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The bigger I am, the harder they fall.
a b V Motherboard
June 18, 2004 11:26:19 AM

If I were you, before I went out buying memory I'd think about figuring out if anything can be done to increase the bus speed first.

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<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>
June 18, 2004 11:30:13 AM

I hear what you're saying but The main reason I'm upgrading is to get 1GB into my system, the applications I'm running are very resource hungry 512 just doesn't cut it.

I just thought that if I was going to upgrade to 1GB, would I need PC2700, or could I make do with cheaper 2100 but the price difference ain't so large and so it'll be 2700 or 3200 if it's not much more expensive.

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The bigger I am, the harder they fall.
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