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What CPU for Latitude C840?

post #1 of 16
4/18/06 at 10:06pm
Thread Starter 
I bought a barebones Latitude C840 on eBay at a reasonable price, but it has no CPU.
I haven't been able to find a lot of information about what is compatible.
I see them with up to 2.2GHZ (and I want the fastest I can get), but what should I look for, and what is the best bang for the buck?
I think the system has a 400FSB so no sense wasting money on a 533FSB.
My biggest confusion seems to be how many pins does the CPU I need have.
Is it 479 or 478?
Any assistance would be welcome, this is going to be my most challenging build yet.
Should I even consider a Celeron M?
I suppose that would need a bios flash huh?
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post #2 of 16
4/19/06 at 5:20am
I've upgraded the CPU in my Inspiron 8200 (runs a C840 BIOS) from a 1.6 to a 1.9 P4 without any difficulty. Unfortunately you're stuck a 2.2Ghz...that's as high as they made the P4m. Anything higher speed on eBay labeled as a P4m is a desktop P4 pulled from a notebook. The CPU for a C840 has no Heatspreader and has speedstep. It is socket 478. Personally, I'd avoid putting a Celeron in the system, I've installed Celerons in my notebook for testing purposes and they pale in comparison to a P4m's performance.
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post #3 of 16
4/19/06 at 10:17am
Thread Starter 
Thanks again MrEvil, sounds like you should know.
You said that the CPU for a C840 has no Heatspreader and has speedstep.
You've brought up points I hadn't even known about.
I imagine the heatspreader is the little platform that the chip sits on.
(recently converted desktop guy here)
Do they make P4 Ms with heatspreaders and without speedstep, and how would I know what to look for?
Since I don't know what CPU was in there, are there any other little surprizes that I should know about?
I only see one Bios flash update available on the DEll driver/support webpage.
Will I need to flash the bios?

I saw a QrQ5 P4-M 2.2GHZ available, would that work?
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post #4 of 16
4/19/06 at 6:30pm
There is no heatspreader on the P4m Models and rather cheap/easy to find on parts chains or eBay.
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post #5 of 16
4/20/06 at 12:55am
I think the c840 can take up to a 2.6Ghz mobile P4-m. If I'm not mistaken it has the same motherboard as an Inspiron 8200. I've read that the 8200s can go up to a 2.6. Someone correct me if I'm wrong.
My Inspiron 8200 has a 2.2 right now (sSpec SL6VB).
2.2s are about $50 on ebay right now and 2.4s are about $75. I myself am looking for a reasonably priced 2.6 but with the current prices, I see no point in upgrading. Just remember what MrEvil said, the processors with the heatspreader are desktop processors and are not what you're looking for.
I always verify the sSpec# with the seller to make sure that it is a mobile Pentium 4-m.
Here's a great guide:

http://processorfinder.intel.com

Select mobile intel pentium 4 processor - m from the drop down menu.

Hope this helps.
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post #6 of 16
4/20/06 at 1:24pm
I had an old spare p4m chip just laying around and I can confirm that it must be a heatspreaderless chip.
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post #7 of 16
4/20/06 at 8:27pm
Thread Starter 
The processor link was very helpful. thanks.
I am drawn between the SL6VC 2.4GHZ (for over $100)
and the SL6J5 2.2GHZ for about $50 (eBay prices)
I haven't seen where the c840 uses a faster than 2.5GHZ.
I want the speed and best bang for the buck.....
how much real performance differnece is there between the 2.2GHZ and the 2.4GHZ?
(yeah, I know .2GHZ...but in real life application???????)
I did notice a bump up when I Overclocked my 2.2GHZ to 2.4GHZ (AMD 3700+)
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post #8 of 16
4/21/06 at 1:23am
At those prices the 2.2 would be the reasonable upgrade. The .2 Ghz is not worth $50.
The 2.2 runs pretty fast on my Inspiron 8200. It scores almost exactly the same as the 1.6 Pentium m I have in my Inspiron 700m using PCmark 2002.
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post #9 of 16
4/22/06 at 12:41am
Quote:
Originally Posted by at2wooden
Thanks again MrEvil, sounds like you should know.
You said that the CPU for a C840 has no Heatspreader and has speedstep.
You've brought up points I hadn't even known about.
I imagine the heatspreader is the little platform that the chip sits on.
(recently converted desktop guy here)
Do they make P4 Ms with heatspreaders and without speedstep, and how would I know what to look for?
Since I don't know what CPU was in there, are there any other little surprizes that I should know about?
I only see one Bios flash update available on the DEll driver/support webpage.
Will I need to flash the bios?

I saw a QrQ5 P4-M 2.2GHZ available, would that work?
The Heatspreader is that little metal plate that's on top of the CPU die. If you've seen a Desktop P4 compared to a P3, you'll notice the P4 has a metal plate covering up the CPU core where the P3 doesn't. P4m CPUs dont' have this Integrated Heat Spreader. The other "mobile" P4s you see on eBay that have the IHS are in fact desktop CPUs that were pulled from a Laptop that used Desktop CPUs.
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post #10 of 16
4/22/06 at 9:07pm
Thread Starter 
does it make any difference if the core stepping is C1 or D1?
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post #11 of 16
4/23/06 at 2:37pm
You would want D1. The core stepping tells you basically when the CPU was made and D1 would mean that the CPU was made at a much later date then the C1 version. Why would you want a new core stepping? New cores mean the CPU went thru minor revisions which could lead to better manufacturering process to make the cpu run cooler and as lots of overclockers will tell you also run at higher clock speeds if you were looking to overclock.
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post #12 of 16
4/23/06 at 10:05pm
Thread Starter 
oooooooooooooo now you are talking !!
Since I am new to lappies I have to ask....
Is OC realistic?
I am not familiar with the Intel 845MP chipset.
Altho, I suspect it is not unsimilar to the intel 845.
I didn't see any overclocking programs built into the C840.
While on the topic, is the Nvidia 64 card something that coolbits or nvtweak would improve on?

I imagine it is almost impossible to control the heat increase to get a respectable OC.

Please do go on

C840 under constuction.....
p4 m 2.4ghz 1gb ram 64 mb NVIDIA GEFORCE4GO DVD burner
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post #13 of 16
4/23/06 at 10:22pm
Overclocking would be unrealistic and probabaly impossible for the CPU on your notebook. Of course the CPU itself are great overclockers if you ever decided to plop one into a desktop. The video card can be overclocked although a ireccomend against it. Most Geforce440's were golden overclockers on that line of notebooks but the stress it created on th ecustom interface port made then suceptable to damage because of the high heat the motherboard wasnt designed to tolerate.
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post #14 of 16
4/23/06 at 10:28pm
Thread Starter 
That's ok, I imagine the way it will be when I finish will be more than enough for my needs.
I like this forum
Only one last question comes to mind (for now)
Do I use thermal paste between the CPU and heatsink? (silly, right?)
From picture of some of the CPUs that I have seem they almost look like they have a cover or something.
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post #15 of 16
4/24/06 at 6:29pm
People say it helps so it couldnt hurt to use a little right?
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post #16 of 16
4/24/06 at 9:42pm
Thread Starter 
thanks again........still waiting on parts.
Hope to have the last of them next week.
Hope the MB is good
Looking forward to the project
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