RAM allocation?

Hi,

If I have 8GB of RAM and I allocate 4GB for MAC OS and another 4GB for Windows. Does RAM for MAC is constantly allocated on 4GB or It is on 8GB and it will be split when I start windows with Parallels software?

Thanks

 

Neither.

When Parallels (and subsequently the Windows VM) is not running, OS X has all the RAM for itself.
Once the Windows VM is started it starts expanding the used RAM as needed up to the allocated limit, this means that if Windows is using 1.5 GB out of 4 GB, this will only take 1.5 GB (plus about 500 MB for the Parallels app itself) from OS X.
Once the VM is shut down, the RAM is given back to OS X.

 

Can I change allocated limit during work for example I allocate 4GB for Windows VM and I need more? Can I simply add more RAMs?

From your reply I can conclude, this allocation is dynamic. You reserve maximum limit and It is not full used. It use as it need.

 

You can't change the allocated RAM of an OS that is running, you'll have to shut down Windows first.

The allocation is dynamic although as far as Windows is concerned Windows always has 4 GB available. Dynamic here is just that Parallels doesn't tell OS X to reserve the whole 4 GB for it, it asks for more up until 4 GB, but for Windows it's always 4 GB that it sees.