I'm exploring Cloud Computing. The first thing you get to learn is horizontal/vertical scaling. In horizontal scaling you simply add a new server (image) to your existing servers. In vertical scaling you add new hardware (CPU/RAM) to your same server.

Then you read something like "most Operating Systems don't allow adding hardware without rebooting"

So my question is: Are there any Operating Systems that would allow me to add RAM for example without rebooting?

  • You can do that to a virtual OS (VM) but not a real OS.
    – DavidPostill
    Jul 8, 2017 at 13:29
  • Thanks for the comment. I'm playing with Oracl Virtual Box. And while my image is running, I can't add RAM or CPU cores. Or are there other VM managers that allow you to add RAM/CPU while running?
    – AhmedWas
    Jul 8, 2017 at 13:32
  • VirtualBox doesn't support it but other hypervisors actually do
    – Ramhound
    Jul 8, 2017 at 13:41
  • I think bigger players have so much vertical scaling, that it doesn't matter and most bigger players also have a custom linux, built from ground up and keeping in mind to support hot swapping, I think it goes by something, that pc is given a notice to empty up memory from stick 3 and then swappeed, but i belive you need to swap them one by one, leaving at least 1 stick in. Jul 8, 2017 at 13:49
  • @Ramhound please check Andrew Lamarra's answer and let me know what you think. Thanks!
    – AhmedWas
    Jul 8, 2017 at 14:09

1 Answer 1


I tested this on 3 hypervisors (VirtualBox, VMWare Workstation 12.5, and VMWare ESXi 6.0 via the Embedded Host Client) and several OS's (Windows Server 2k8, Windows 7, and Ubuntu Server 16.04). None of the hypervisor software would even give me the option to increase CPU's or RAM while the machines were running. Even if they gave me the option, I doubt the OS would take the change w/out a reboot.

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