Technical information

Performance Best Practices for VMware vSphere 4.0
46 VMware, Inc.
NIC
Historically meant “network interface card.” With the recent availability of multi-port network cards, as
well as the inclusion of network ports directly on system boards, the term NIC is now sometimes used to
mean “network interface controller” (of which there may be more than one on a physical network card or
system board).
NIC Morphing
The automatic conversion on some guest operating systems from the vlance virtual network adapter to
the higher-performance VMXNET virtual network adapter.
NIC Team
The association of multiple NICs with a single virtual switch to form a team. Such teams can provide
passive failover and share traffic loads between members of physical and virtual networks.
Non-Uniform Memory Access (NUMA)
A computer architecture in which memory located closer to a particular processor is accessed with less
delay than memory located farther from that processor.
Nonpersistent Disk
All disk writes issued by software running inside a virtual machine with a nonpersistent virtual disk
appear to be written to disk, but are in fact discarded after the session is powered down. As a result, a disk
in nonpersistent mode is not modified by activity in the virtual machine. See also Persistent Disk.
NPT (Nested Page Tables)
AMD’s implementation of hardware virtual MMU. Also called RVI.
P Pacifica
A code name for AMD’s version of virtualization assist, included in some 64-bit AMD processors. See
AMD Virtualization.
Paravirtualization
Paravirtualization is a technique in which a modified guest operating system kernel communicates to the
hypervisor its intent to perform privileged CPU and memory operations. See also VMI.
PCI (Peripheral Component Interconnect)
A computer bus specification. Now largely being superseded by PCIe.
PCI-X ()
A computer bus specification. Similar to PCI, but twice as wide and with a faster clock. Shares some
compatibility with PCI devices (that is, PCI-X cards can sometimes be used in PCI slots and PCI cards can
sometimes be used in PCI-X slots).
PCIe (PCI Express)
A computer bus specification. PCIe is available in a variety of different capacities (number of “lanes”): x1,
x2, x4, x8, x16, and x32. Smaller cards will fit into larger slots, but not the reverse. PCIe is not
slot-compatible with either PCI or PCI-X.
Persistent Disk
All disk writes issued by software running inside a virtual machine are immediately and permanently
written to a persistent virtual disk. As a result, a disk in persistent mode behaves like a conventional disk
drive on a physical computer. See also Nonpersistent Disk.
Physical CPU
A processor within a physical machine. See also Virtual CPU.
Preallocated Disk
A type of virtual disk in which all the host disk space for the virtual machine is allocated at the time the
virtual disk is created. See also Growable Disk.