Cbarnhorst said:
Virtualized memory is not handled the same way as host system memory so be conservative. Don't exceed the recommended memory allocation in order to keep cpu overhead down. The host cpu plays a more important role in memory management for the guest than it does for native ram (which is handled by the memory manager in hardware). The greater the allocation the greater the overhead on the cpu. 1 GB should be fine for most Linux distributions. Since you can adjust with experience, start conservatively.

Hi there

not quite true -- you DO need enough left over for the HOST to run the VM software properly without paging / swapping.

Also the better VM software uses Dynamic RAM so the VM whatever you allocate it will only be the maximum you specify in the config file. When the VM is idle that RAM is available again for the HOST.

Older versions of VM software fixed the allocation from your config file so the Host memory was always memory available MINUS the amount you'd allocated for the VM even when the VM was idle.

CPU isn't usually a problem on VM's -- RAM and decent I/O play a much bigger role --- this is of course assuming typical tasks a VM does like file serving, media streaming, office type apps such as email, skype etc.

CPU will count if your VM needs to do things like video editing, game playing, intensive photoshop etc.

Even here if you have a decent graphics card the CPU requirement can be minimized provided the VM can use the hardware graphics card rather than the "default" built in ones when using say VBOX or VMWARE.

I've generally found I can get pretty decent performance out of a fairly well loaded W10 X-64 PRO system VM allocating it 2 GB RAM on a 16 GB RAM server running CENTOS 7 as HOST.

I allocated 60GB HDD space for the W10 VM and stored it on an SSD -- works perfectly and use it almost daily --has Office 2016, Photoshop, SAPGUI, and quite a bit of other stuff.

On the same machine I have an XP VM running my hardware record Vinyl cutting machine + the studio software for creating the tracks on the Vinyl discs -- this also works fantastically well with 1 GB RAM allocated to it. (I need the XP machine as the hardware won't run on anything newer --it still does the job perfectly - and I don't want to spend a few thousand EUR / USD on new hardware when I don't need to --also no security here with the XP VM as it's isolated from the Internet.