The main principle of Qubes OS is security by compartmentalization (or isolation), in which activities are compartmentalized (or isolated) in separate **qubes**.
However, in casual conversation this is often shortened to `Qubes`, and in technical contexts where spaces are not permitted, (e.g., usernames), the space may be omitted, as in `QubesOS`.
* Example: "In Qubes OS, you do your banking in your 'banking' qube and your web surfing in your 'untrusted' qube. That way, if your 'untrusted' qube is compromised, your banking activities will remain secure."
* "Qube" is an informal term intended to make it easier for less technical users to understand Qubes OS and learn how to use it. In technical discussions, the other, more precise terms defined on this page are to be preferred.
* The term "qube" should be lowercase unless it is the first word in a sentence. Note that starting a sentence with the plural of "qube" (i.e., "Qubes...") can be ambiguous, since it may not be clear whether the referent is a collection of qubes or [Qubes OS](#qubes-os).
**In Qubes OS:** An area or set of activities in one's digital life that has certain security requirements and therefore involves the use of certain [qubes](#qube).
For example, suppose your "email" domain encompasses the activity of sending PGP-encrypted email.
This domain may include your email qube and your [Split GPG](/doc/split-gpg) qube.
Alternatively, "NetVM" may refer to whichever VM is directly connected to a VM for networking purposes.
For example, if `untrusted` is directly connected to `sys-firewall` for network access, then it is accurate to say, "`sys-firewall` is `untrusted`'s NetVM," even though `sys-firewall` is a ProxyVM.
By default, a DisposableVM Template named `fedora-XX-dvm` is created on most Qubes installations (where `XX` is the Fedora version of the default TemplateVM).
DisposableVM Templates are not [TemplateVMs](#templatevm), since (being TemplateBasedVMs) they do not have root filesystems of their own to provide to other VMs.
Rather, DisposableVM Templates are complementary to TemplateVMs insofar as DisposableVM Templates provide their own user filesystems to the DisposableVMs based on them.
An efficient and lightweight virtualization technique originally introduced by the Xen Project and later adopted by other virtualization platforms.
Unlike HVMs, paravirtualized [VMs](#vm) do not require virtualization extensions from the host CPU.
However, paravirtualized VMs require a PV-enabled kernel and PV drivers, so the guests are aware of the hypervisor and can run efficiently without emulation or virtual emulated hardware.
Any fully virtualized, or hardware-assisted, [VM](#vm) utilizing the virtualization extensions of the host CPU.
Although HVMs are typically slower than paravirtualized VMs due to the required emulation, HVMs allow the user to create domains based on any operating system.
To boost performance, fully virtualized HVM guests can use special paravirtual device drivers (PVHVM or PV-on-HVM drivers).
These drivers are optimized PV drivers for HVM environments and bypass the emulation for disk and network I/O, thus providing PV-like (or better) performance on HVM systems.
This allows for optimal performance on guest operating systems such as Windows.
