ram upgrades on Lenovo T420S

techs, I have constantly seen in the specs of Lenovo's laptop that it will take a max 8 gigs? Now my question is, if I have windows 7 and it has 2 slots, why cannot I add up to as much ram as will fit? Instead of 2 4 gig dims why not 2 8 gig dims or 2 whatever  to get past 8 gigs?
Dennis MillerAsked:
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Gary CaseConnect With a Mentor RetiredCommented:
... as an example, I built a small server with this motherboard a couple years ago:
http://www.supermicro.com/products/motherboard/ATOM/ICH9/X7SPA-HF-D525.cfm

Note the specifications indicate " ... Up to 4GB single channel unbuffered, non-ECC DDR3 800MHz SO-DIMM"

... Since the chipset and CPU both had higher density support, I tried using a pair of 4GB modules when I built the system -- it's been running very happily with 8GB of RAM ever since I first turned it on :-)

-- I've seen numerous other examples of this over the years; so I always check the chipset capabilities (or simply try larger modules) before assuming a system won't support more than the original technical documents say.
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Nick RhodeConnect With a Mentor IT DirectorCommented:
Its because the board (motherboard) can only support up to 8gb, this is hardware related and how many address lines are wired to the board.  Anything beyond 8gb would be useless with the current hardware in the system you have.
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Leon KammerCommented:
The amount of RAM you can use in a Computer is limited by the Processor and IC manufacturers.
It basically boils down to how many memory ranks a certain CPU can support.

ark.intel.com states that the CPU can support up to 16GB of RAM assuming you are using the Intel Core-i3 2310M
However, this is over 2 memory channels, since the laptop only has 2 slots (1 memory channel), the maximum that a single channel can use is 8GB

Cheers

Leon
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Gary CaseRetiredCommented:
"... why cannot I add up to as much ram as will fit? Instead of 2 4 gig dims why not 2 8 gig dims or 2 whatever  to get past 8 gigs? "  ==>  The simple answer is you MIGHT be able to do that.

The QM67 Express chipset your system uses supports 8GB modules; and all of the CPU's offered with this system support 16GB.    But the BIOS may not support 8GB modules, or the motherboard design may restrict the addressing so you can't use larger than 4GB modules.

I've seen several systems that will support larger modules than their technical documents say they will -- in these cases it's usually simply a disconnect between the tech writers (who based their specs on the largest modules available at the time) and the actual physical capabilities of the hardware.

USUALLY the specifications are correct -- if that's the case, you're indeed limited to 8GB total.   But the only way to KNOW for certain is to simply try an 8GB module and see if the system recognizes it.   It will NOT cause any harm to do that -- the worst case is it simply won't work;  the most likely case is it will only recognize 4GB of the module;  or if you get lucky it will work fine :-)
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Leon KammerConnect With a Mentor Commented:
Gary is in fact correct, there is fact four models within the Lenovo T420S range that have a BIOS that supports 16GB RAM (2x8GB  204pin sodimm 8 Chips (16 chips does not work on 100% of machines)).
These are :
4170-xxx
4171-xxx
4173-xxx and
4174-xxx
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rindiConnect With a Mentor Commented:
Your PC might have been produced before DDR 3 modules were developed with of 8GB size, so at that time it would only have supported 8GB max. Sometimes PC manufacturers will update their documentation as larger modules come out, sometimes they don't. Besides that, very often only certain modules of certain manufacturers will work, and those that work are usually also listed in some documentation.

Generally it is best to take a PC you want to upgrade the RAM for along to a PC shop, and ask there whether you can try it with the larger RAM. If it works, you buy the new RAM and everything is OK, if it doesn't work, it's not your loss, and the shop keeper just lost some time, and you might buy something else anyway... Most shops allow you to test things that way, at least where I live. Some even allow you to take the RAM home to test it, and they take it back if it doesn't, but that you'd have to verify with the shop keeper first!
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Dennis MillerAuthor Commented:
wow. I have been sent back to school. This is all great too bad we cannot give you all 500 points. This is a class on  ram. Excellent answers and thanks a great deal.
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Dennis MillerAuthor Commented:
To anyone who needs help on why only so much ram will work, you will not get a better answer anywhere. Great response and excellent help. Thanks so much.
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