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I have an HP Probook 4740s running windows 7 Professional which came with 4GB of RAM.

I just upgraded the RAM by adding another 8GB in the free slot.

However, Windows now takes a lot longer to start up (feels like about 3 times or more).

In addition, applications seem to respond more sluggishly.

Windows (in the My Computer properties) is reporting 12GB of RAM.

I didn't expect that the laptop would be faster, only to be able to run more programs comfortably without swapping slowing it down when switching between them (as I was maxing out the available memory already). I did not expect Windows to perform worse.

Can you think of any reasons why it could hamper performance?

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What is windows reporting as the currently installed memory after the upgrade (right click My Computer and go to properties to find it)? If you went over the motherboards limit for max RAM that could cause the problem. –  Scott Chamberlain Sep 5 '13 at 6:29
    
Windows is reporting 12GB (I added the detail to my question as per SE guidelines). –  mydoghasworms Sep 5 '13 at 7:01

2 Answers 2

up vote 6 down vote accepted

As per Factory Specs

Memory, maximum
8 GB 1333 MHz DDR3 SDRAM

As your have breached this limit by running 12GB I'm not surprised your experiencing performance issues.

Note:

This was a partial answer. I don't know why breaching this limitation affects performance, I just know it does


Thoughts on this limitation

Hardware limitations on maximum ram capacity is what caused the issue but why?

It would appear that windows could see all the available capacity of RAM but when trying to address certain regions which it believed were available it was failing due to the hardware limitation. As such it was experiencing lagging well trying to search for available segments.

But this leaves a few more question:

  • Why did it go past POST when a hardware limitation was breached?
  • Why was windows unable to detect the limitation?
  • Why wasn't windows displaying errors instead of running slower?

I hope someone with more experience is able to shed some light on why this behavior occurs when the hardware limitation is breached

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Most likely the bios does not recognize the new RAM at all so if he had 2x 2GB before and replaced one of them with the 8GB stick it now only sees the one 2GB stick. –  Scott Chamberlain Sep 5 '13 at 6:34
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He said he added it to a free slot and if it's like most HP laptops I pull apart they like to use 4GB sticks over 2x 2GB (Probably cheaper) –  50-3 Sep 5 '13 at 6:37
    
Mmm, that's interesting about the maximum memory. Thanks for pointing that out. I will uninstall the original 4GB memory and see if that helps, although Windows does recognize the 12GB of RAM correctly. Let me see if downgrading to 8GB will make it better. –  mydoghasworms Sep 5 '13 at 7:02
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Try memtest86, memtest86+ or Windows Memory Diagnostic, that will give lots of info about your memory –  golimar Sep 5 '13 at 8:01
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Well, going down to 8GB memory has dramatically improved the performance of my machine, so even though I don't know the detail, this answer is good enough for me. Thanks! –  mydoghasworms Sep 5 '13 at 8:29

It is a dual-channel motherboard that you forced into a slow single-channel mode by using 2 different sticks of RAM.
This can severely hamper performance, especially if the sticks have a different speed-rating too.
Single channel-single stick is often a lot faster than single channel with 2 sticks.

That 8 GB limit stated by HP is bogus. Windows wouldn't be able to see 12 if that was the case.
That motherboard (Intel HM76 chipset) should be able to take up to 2x8 GB according to Intel.

HP (and a lot of other manufacturers) are known to "limit" the maximum RAM in their specs if, at the time of writing of the specs, they don't offer those particular SO-DIMMS as an upgrade or option.
Those specs rarely get adjusted if such RAM becomes available later.

That doesn't mean it won't work, unless they specifically programmed the BIOS to prohibit this, which is very rare. (And in that case the laptop wouldn't get past POST.)

Always check the motherboard chipset/CPU specs for the real story. The motherboard chipset or the CPU in 99 out of the 100 cases is the limiting factor when it comes to maximum RAM specifications.

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It's your answer which is bogus. The Serial Presence Detect chips on the DIMMs (SPD) will report all 12 GB, because that feature doesn't use the address lines. But if you simply don't have the address lines to send address 0x000 00002 0000 0000, then you can't use those reported 12 GB. –  MSalters Sep 5 '13 at 10:11
    
@MSalters You are in the wrong: Windows would not even be able to boot unless the memory is really usable. As Windows DOES boot in this config the memory is really there and usable. Don't downmod unless you have really thought the matter through. I checked the Intel manufacturer docs on this motherboard chipset. Not wiring the extra address-lines is not supported by the chipset anyway, so it is even technically not possible to have the system support less than 16 GB. (Unless by artificially software-limiting in BIOS, but then the system shouldn't POST with > 8 GB.) –  Tonny Sep 5 '13 at 13:35

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