MBP 2011 uses more RAM than MBP 2008

[OngL]

I have a solid MBP 2008 Unibody running on 10.6.7. With a fresh install, I have used about 988 MB of RAM from iStatMenu, right after boot-up. If I moved the exact same HDD to MBP 2011 i7, upon boot-up it will use 1.35GB RAM.

The only difference I can see is that the MBP 2008 has 256 MB shared video memory and MBP 2011 has 384 MB. The only difference is about 128 MB, however, the net difference of RAM used after boot-up from the same HDD, it about 400 MB.

Any idea where does the difference go? I mean afterall, it is the same OS and same drive with same apps loaded at boot time. 400 MB is quite a premium even if I have 8GB of RAM.

 

[Hellhammer]

If you have more RAM in your new MBP, that explains it. The more RAM you have, the more your apps will use it.

 

[sammich]

Apps runs faster and are more responsive when they use more RAM. They spread out comfortably, so to speak. When they have less room to 'maneuver' they'll have to do things like page out, which means accessing the HDD/SDD which is much slower than RAM.

 

[dal20402]

To be more precise about the above responses (which are basically correct), the system will load more information into memory when it knows it has more RAM available. If you happen to perform an operation that needs the extra items loaded into memory, it will happen faster.

My fresh install, configured pretty much the same way, uses about 600 MB on my 2 GB 2006 MBP and about 1.8 GB on my 12 GB hackintosh right after bootup.

 

[OngL]

Interesting, I overlooked to mentioned that both machines has DDR3 8GB installed on them... So one theory of having more memory with more apps using them at boot-up seems plausible.. In my case, they have both same memory, so why the 400MB difference...

I'm basing my memory used on Wired and Active memory only, not inactive...

Thanks for the input so far.

 

[OngL]

For everyone benefit, one of the answer given to me from another forums, it seems 2011 MBPs default to 64-bit kernel which uses more memory. I checked my MBP 2008, it defaults to 32-bit kernel. As I'm using the same HDD, it must have been stored in PRAM or NVRAM in each machine.

Now, what is the implication of NOT booting to 64 bit? My MBP 2008 has 8GB ram but yet I wonder why it went to 32 bit on Snow Leopard 10.6.7.

 

[YanniDepp]

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8F190 Safari/6533.18.5)

64-bit kernels can only load 64-bit kernel extensions (i.e. drivers), and since a lot of hardware only has 32-bit kernel extensions, older Macs defaulted to 32 bit kernels. Snow Leopard still pretty much ran in 64 bit mode, running 64 bit apps and seeing over 4GB of RAM, but the kernel itself still ran in 32-bit.