[asharp]

This makes sense when you keep in mind how the older clouds work (essentially VPS providers 101).

You have a server with some disks, some ram and some cpus. You aggregate the disks together, then split them to form the individual disks for the virtual machines. You then use kvm/xen to provide isolation as well as to split the ram/cpu between the virtual machines.

So to answer your question: Storage/ram/cpu is sold in lock step because otherwise there would be resources sitting on servers that are unable to be sold. Bandwidth isn't constrained like that because bandwidth isn't a thing tied to a machine.

There are some providers out there that don't lock ram/disk together. This is mostly because they use a distributed storage pool rather than local disks. This is significantly more complex and is a 'fairly' new addition to the scene (~2010?).

This is also why certain providers still charge you for ram even when your machine is turned off, and why backups/migra tions/plan upgrades can be a bit of a pain in the neck at times.