reboot your host, open up task manager and see how much memory is being used between windows services and vmware. i figure you'll be somewhere around the 120-150MB range if your host does not have anything else heavy running in the background (sql, exchange, etc)
if the host is purely for vmware then i would add a couple hundred MB to be safe then allocate the rest for your VM's. there is no magic number for this, just test and see what works best for you.
We used to say about 512MB which proved to be a good number. This takes host OS, VMware Server and vm overhead into consideration.
VMWare needs the following overhead, based on the amount of RAM assigned to the guest:
For machines Memory <= 512MB, its about 10%
For machines 512MB < Memory <= 1000MB, its about 6%
For machines 1000MB < Memory <= 2000MB, its about 4%
For machines 2000MB < Memory <= 3600MB, its about 3%
There will also be a little required for things such as the video memory, etc. So, for a machine with 1GB, you are looking at around 4%, per machine, so to run 6 of them, you want 6 and a quarter of a gig for the machines alone, then you want some more for the host itself to use.
To eeek out as much performance as possible, I'd be making sure I was configuring my memory to be dual channel, and if a typical machine has 4 slots for memory, I'd be populating them with 2GB sticks, to make 8GB in total. Its a little generous, but hey, you never know when you need a little more.
From the VMware Server documentation ( page 156 )
Amount of Memory Allocated to the Virtual Machine, Additional Amount of
Up to 512MB Up to 54MB
Up to 1000MB Up to 62MB
Up to 2000MB Up to 79MB
Up to 3600MB Up to 105MB
Hey Kevin! Thats exactly where I lifted my figures from! I just converted them to percentages
Great minds think alike
So who gets the "correct" answer?
i quoted nothing and got first post