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Dell Laptop Does not See Ram


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#1 tobbyjr

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Posted 24 March 2009 - 07:18 AM

I have a Dell Inspirion 600M Laptop running windows XP Pro,,,it came with 512Mb of ram installed,,( 256mb in slot A and 256mb in slot B,,),,

I bought two 1gig sticks of PC2700 DDR SODIMM 200pin 333mhz CL 2.5,,,installed both and the laptop comes on for about 3 seconds then reboots over and over.

I removed the 1 gig stick from slot B and the laptop does the same thing,,

I removed the 1 gig stick from slot A, put the 256 stick back in and put a 1 gig stick in slot B and computer boots sees both sticks.

I have tried both 1 gig sticks this way and both are seen by the laptop, so I am pretty sure both 1gig sticks are find,,,

My problem is the laptop will not recognize either 1 gig sticks in slot A, but will recognize them in slot B,,only the 256 is seen in slot A,,

any Ideas..

Thanks,,,

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#2 hamluis

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Posted 24 March 2009 - 10:15 AM

Yep...sounds like you have the wrong speed or timings with your purchased SODIMMs.

I had a similar problem about 3 months ago with a desktop.

The reason the system works with the original and either new module...is because the RAM collectively defaults to the slower speed when two dissimilar modules are installed.

The reason it won't work with the new alone...is speed/timings.

I found a workaround for my situation...I went into the BIOS and adjusted the RAM clock down from 200 to 166...and I was then able to install the newer (larger modules) RAM and not have the system go haywire.

If you run Memtest on all the modules, you will see what I mean by speed differences.

Memtest86.com - Memory Diagnostic - http://www.memtest86.com/

Louis

#3 tobbyjr

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Posted 24 March 2009 - 02:44 PM

That make sense, but I thought that ddr ram was backwards compatible,,,I will take a look in cmos settings, run memtest also,,

Thanks

#4 hamluis

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Posted 24 March 2009 - 03:47 PM

The problem lies not in the RAM...but in the motherboard.

Some boards are more finicky/particular than others, while some will function fine if the RAM modules are even close to what is specified.

Add to that the possibility that there could be minute differences in each/every module (because humans are involved in the quality control process)...and it's not as simple as some might think.

Taken from http://www.kitchentablecomputers.com/ram2.htm:

RAM Speed
The speed of RAM you will need depends mainly on the motherboard. You generally should choose the highest speed of RAM that the motherboard supports. Make sure that you check the motherboard documentation to find this out. Just because a stick of RAM fits in a motherboard doesn't mean it will work. Sometimes, inserting the wrong RAM and powering up the mobo can damage the board, the RAM, or both.

Even if your motherboard can support different RAM speeds, using slower RAM than the fastest that the mobo supports means you won't get the maximum performance that the board is capable of delivering.

As the speed capabilities of RAM of a given type improve, newer, faster RAM is usually backward-compatible to slower speeds. This is accomplished through the use of a serial presence detection circuit built into the RAM module. So for example, most PC-2700 (333 MHz) DDR-SDRAM sticks are backward-compatible to PC-2100 (266 MHz). So if your board is built for PC-2100, but you can get PC-2700 for the same price, you may as well go for the faster RAM. You never know: You may want to use it in your next project. (Just make sure that the RAM you buy is backward-compatible to the speed you need now!)

The one thing you generally should avoid, however, is mixing RAM speeds in the same computer. In theory, if you mix RAM speeds, all of the modules should clock to the lowest speed; but in practice, mixing speeds (and sometimes even brands) in the same PC can cause system instability. (And of course, RAMBUS and dual-channel DDR must use matched pairs of identical modules.)

So, in summary, even though different brands of RAM (and to an extent, different sizes and speeds, except for RAMBUS) can theoretically be mixed, we continue to recommend using identical RAM sticks in any given computer to maximize stability and minimize the possibility of conflicts.


There are other factors but I'm not trying to be exhaustive...just provide some understanding of how UN-simple it may be.

If you really want more pedantic detail, A Guide to Memory Timing - http://www.amd.com/us-en/Processors/Comput...5E13335,00.html

All of the above...is one reason why more persons ought to take advantage of memory configurators which are available at various RAM vendors. Relying on these results (generally) in RAM which is guaranteed to run in the system/motherboard for which it is specified.

Louis




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