Introduction to Virtualization - Oracle Solaris 10 System Virtualization Essentials - page 33

the hypervisor. Adding these features increases the complexity of the hypervisor,
making it more like an OS.
Type 1 hypervisors generally use one VE as a management environment. The
administrator interacts with that VE via the system console or via the network.
That VE contains tools to create and otherwise manage the hypervisor and the
other VEs, usually called guests . Some Type 1 systems also allow for one or more
specialized VEs that virtualize I/O devices for the other VEs. Figure 1.19 shows
the overall structure of a Type 1 hypervisor implementation, including a virtual
management environment (VME) and a virtual I/O (VIO) VE.

Figure 1.19 Virtual Machines and a Hypervisor

Hypervisors that offer VIO guests typically provide an alternative to their use:
direct, exclusive access to I/O devices for some VEs. Direct access offers better
I/O performance but limits the number of VEs that can run on the system. If the
system has only four network connectors, for example, then only four VEs can
have direct network access.

1.2.2.2 Industry Examples
IBM developed the first hypervisors (and coined the term) for its mainframes in
the 1960s. 3 VM/370 was a popular hypervisor for IBM mainframes starting in
1972. Its descendant on current mainframes is z/VM, which supports virtual
machines running IBM operating systems such as z/OS and z/VM (nested vir-
tual machine environments are possible), and open operating systems including
several distributions of Linux and an experimental port of OpenSolaris.
VMware Inc.'s VMware ESX is a Type 1 hypervisor for x86 systems. It sup-
ports common operating systems such as Microsoft Windows, Oracle Solaris, and
some releases of Linux distributions such as CentOS, Debian, Red Hat Enterprise
Linux, Novell SUSE Linux, and Ubuntu. Its VMC is called the service console .

3. The Appendix contains a detailed narrative of the history of virtualization.