virtualbox.org

The manual says:
Depending on your selection, VirtualBox will enable or disable certain VM settings that your guest operating system may require.
http://www.virtualbox.org/manual/ch01.html#gui-createvm

But, are there any optimizations beside of that?

Not really, you can install Linux on the Windows profiles and Windows on the Linux one. Of course, depending on the version of the OS, installation is supported with the default settings.

Thanks for the info.

But how can it be...
On another thread there was a discussion about this. He says he uses a Phenom (AMD) and a known issue for AMD is that Win32-Guests run slower on those CPUs. He claims that if he uses any Win32-Setting the guest runs slower. But if he uses any Win64-Setting the Win32 Guest runs faster. But the guest is still the same. The host is Windows 7 Ultimate 64-Bit. And using OS-Type Windows7-64Bit and display 3D,256MB the Paint Shop Pro 9 he uses runs faster than with 128MB.

Let me get this straight.
Win32-Guest, OSType Win32, Phenom, slower
Win32-Guest, OSType Win64, Phenom, faster
Can it be that easy?

If what he says is true, perhaps only AMD-CPUs are affected this way, caused by the known issue AMD/Win32Guest/slower.

I believe you. And i couldn't verify this myself on my Intel.

Can his claims be true? Perhaps only Paint Shop Pro 9 runs faster with 256MB. But if it does, i don't exactly know how.

Sounds like vague gossip to me.

Can you provide specific examples of incorrect settings? Or a proper link to an informed discussion?

Only thing I can think of is that in the profile for 64 bit Windows is a setting that is enabled which isn't for the 32 bit. So, to really test this, you install the Guest using Windows 32 bit as base, then test a few things, shut it down, change the OS to 64 bit and test them again. Check the settings one by one, compare the xml files if you need to, but there should not be any difference whatsoever.

I have found the link to the diskussion on the german board.

Videospeicher
viewtopic.php?f=5&t=43814&p=200581#p196949

The discussion itself contains speculation. The posters described their experiences and were uncertain as to the reason for the results. I do know that certain settings can be different between 32 and 64 bit VMs. For example, I was able to allocate 256 MB video RAM to a 32 bit guest by using settings for a 64 bit VM. But the discussion in the thread you quoted goes further than what I just described. One can only hope that someone with the technical insight such as michaln or Frank Mehnert (no intention to exclude others) explain the matter. On the other hand, you can follow Sasquatch's advise and then you will know what works for you and add to the discussion you quoted above.

I may be on completely the wrong track here, but there is one pretty fundamental difference in VBox when running 32bit or 64 bit guests. 32bit guests can run with or without harware virtualisation whilst 64bit guests only run with hardware virtualisation enabled. This means if a 32 bit guest is set up to run with hardware virtualisation disabled it will run considerably slower. If for some reason the 32bit profile being used has hardware virtualisation disabled by default anything installed with that profile will run slower than if it were installed on a 64 bit profile giving the impression the 32 bit profile is somehow inherantly slower when, in fact, it could be brought up to the same speed as the 64bit profile by changing just one setting.