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Situation: I have a DELL Precision M4500 laptop with Win7 Pro 64bit. Yesterday I upgraded from 8GB RAM to 16GB RAM (2 slots)

[As an aside, upgrading was a bit of a gamble because there is a lot of conflicting information when trying to figure out whether 16GB is supported. Intel Processor Specs mention 8GB maximum for a Core i7 Q740, when I ordered the laptop in Belgium a couple of years back 8GB was the max config I could order, while a 16GB option was only available in the US etc. etc. With memory prices so low, I decided to risk it anyway, and the hardware turns out to support 16GB without issues]

So the 16GB is working fine, under Windows I get this information:

Control Panel > System Installed memory 16,0 GB

Task Manager Total Physical Memory 16373 MB

That's nice, but now I want to be able to SWITCH fairly easily between a lower memory footprint and the full 16GB. I do some virtualization in VMWare for studying, and from time to time this involves scenarios where the 8GB proved limiting, so that was the motivation to upgrade to 16GB. On the other hand, my boot drive is only a 120GB SSD, and my C-partition is 64GB. When I'm not planning to do virtualization scenarios that NEED more than 8GB, I would rather NOT use the 16GB, because of its impact (?) on hibernation (and pagefile, although configurable).

Solution: Windows offers the option to specify the maximum memory that it will use in a boot option. So the plan was to create an additional boot entry that limits Windows to 8GB. Configuring this entry was slightly more difficult than expected: the EasyBCD tool to create additional boot entries seems to have trouble to make the "max mem" option work (interface greyed out), but via msconfig it could be set.

But then some odd stuff started to reveal itself:

When I configure the maximum memory option as "8192 MB", I end up with just 7,24GB usable! (note:when I boot with full 16GB, I have 16373 MB so I don't "lose" any memory in THAT case) Also, after ENTERING the limit, closing msconfig and launching it again, the limit is DISPLAYED as "0 MB" (will come back to that later)

summary: Maximum Memory 8192 => displayed as 0 ??

System Installed memory 16,0 GB (7,24 GB usable)

Task Manager Total Physical Memory 7413 MB

So I thought, "let's just specify slightly more memory, and I'll have about 8GB in total".

So I specified 9000MB. Result: Maximum Memory 9000 => displayed as 808??

System Installed memory 16,0 GB (8,03 GB usable)

Task Manager Total Physical Memory 8221 MB

Although this seems to compensate the issue of "losing" about 700MB of usable RAM, I now experience ANOTHER issue: Windows disables the AERO interface! It looks like it bases itself on the "808MB" value as displayed by msconfig maximum ram advanced boot options.

Any idea what's going on here? What's up with the difference between the maximum memory limit that is DISPLAYED and the one in effect? Why do I lose additional available memory when specifying a limit? Is there a way to force AERO when it THINKS memory is insufficient?

And last question: does specifying the artificial maximum memory limit impact the performance of RAM? For example, if I work with at most 8192MB of RAM, would Windows only use ONE module instead of exploiting dual-channel by using 4 GB on the first 8GB module and 4 GB on the second module?

TIA

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additional information: in Resource Monitor, in 16GB situation, it says "16384 MB Installed" and "16373 MB Total". This is because of 11 MB "Hardware Reserved". But this would lead me to expect that I would also just lose 11MB of available memory when specifying the 8192MB limit... NOT the more than 700MB that I lose now (?) Will check out with the limit set as well. –  JoHel Dec 19 '12 at 12:05
    
Update: in the situation when specifying "8192MB" as maximum memory, Resource Monitor says "16384 MB Installed" and "7413 MB Total". In this case, 8971 MB is identified as "Hardware Reserved"!!! –  JoHel Dec 19 '12 at 12:32
    
Update 2: I re-ran the Windows Experience Index in "9000MB max" scenario, it briefly seemed to re-enable Aero, then disabled it again... –  JoHel Dec 19 '12 at 12:42
    
Update 3: Not possible to force Aero by manually specifying Performance Settings... Initially Windows accepts the setting and enables it, but after a couple of seconds it resets to non-Aero... –  JoHel Dec 19 '12 at 12:59

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