A blog by Jose Barreto, a member of the File Server team at Microsoft.
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Windows Server 2008 Beta 3 memory requirements, as published at http://www.microsoft.com/windowsserver2008/sysreqs.mspx, state that you need a minimum of 512MB of RAM, it is recommended to use 1GB of RAM and the optimal amount of RAM is 2GB for a Full installation and 1GB for a Server Core installation.
However, I imagined that would just make sense that Server Core could run with less RAM than a Full install. How much less, though? With a virtual machine with a brand new Server Core installation of Windows Server 2008 Beta 3 running under Virtual PC, I though it was easy enough to test it. Of course, you should stick to the published specifications, but it was interesting to see what happens if you have less memory.
My installation was a minimum one, with no roles configured. My test procedure was basically to install the system properly with the required 512 MB of RAM, shut it down, lower the amount of memory on Virtual PC, boot the system with the new configuration, logon as Administrator as soon as possible, immediately open Task Manager to inspect system memory, run a few commands (dir, ipconfig, netsh) and finally attempt to perform a clean shut down.
I was surprised to see that the system loaded just fine with 256 MB of RAM, with Task Memory showing 56 MB of free physical memory. It was only at 128 MB that I felt a significant performance hits due to page swapping:
48 MB was the lowest memory where the system was able to run a few comands and shut down gracefully. Below that, the system wouldn't even boot anymore:
I also tried loading another virtual machine, originally configured with a Full instal of Windows Server 2008 Enterprise. I got much less impressive results. With a full install, the 128 MB VM was already swapping a lot, showing 0 MB free physical memory from start. At 64 MB, the system showed a severe performance hit and took over 15 minutes to show the desktop. I didn't try any lower than that.
Another interesting find is that the Windows Server 2008 DVD setup application will require more memory to boot than an already installed server. This happens because it creates a RAM disk. At 128 MB of RAM, the error message from "Windows Boot Manager" reads "Ramdisk device creation failed due to insufficient memory". With 192 MB of RAM, the DVD started to load but froze with a weird dialog box with a red X error icon and a button with no text inside.
With 256 MB of RAM, the DVD loaded properly. However, shortly into the initial wizard, setup refused to proceed with a message saying "Windows detected that the computer has 256 MB of RAM, but 512 MB is required for installation. Installation cannot proceed." I guess that messages do not get any clearer than that. The real interesting fact is that the setup did not complain about running after I gave the system 384 MB of RAM and the installation procedure ran fine.
So the Windows Server 2008 Beta 3 Install says it need 512, won't run with 256 but will not stop you if you have 384, although you will be in unsupported territory.
Although certainly unsupported, 384 MB of RAM seemed like enough memory to run Server Core with a basic role. I got around 150 MB of free physical memory after the system loaded. In fact, I loaded the DNS Server role and still had over 100 MB free...