[I added the numbering.](https://old.reddit.com/r/explainlikeimfive/comments/2atafo/eli5_what_is_a_vm_and_whats_the_point_of_running/ciyk19i/)
>It's a virtual machine. Basically, it's one or more computers pretending to be one or more computers. Believe it or not, this is incredibly useful.
>1. Say you have some services that are busy during the day and others that are busy at night. You need 50 computers to do each of those things. You can now do both with 50 computers by giving priority to VMs based on time of day.
1.1. If you're running some services during the day and other services during the night, then these services won't happen at different times and won't interfere with each other! Why do you need VMs to distinguish these services?
>2. Say you have mission-critical services. You put them on some VMs hosted on a farm of computers. One of the computers has a hardware failure. Without affecting the uptime of the service, you can take the physical machine out of the farm and repair or replace it.
2.1. This sounds like uploading the mission-critical services to a cloud server? Then why do you need VMs? What if the VMs are on the computer that had crashed?
>3. Say you have a lot of little tiny apps that don't really need much power at all. You can put them each on independent VMs, all running on one or two physical computers, saving a boatload of money on hardware.
3.1. If your "tiny apps" "don't really need much power at all", then how can you save money on hardware? Why do you need "independent VMs"?
