Technical information

Performance Best Practices for VMware vSphere 4.0
48 VMware, Inc.
Thrashing
A situation that occurs when virtual or physical memory is not large enough to hold the full working set
of a workload. This mismatch can cause frequent reading from and writing to a paging file, typically
located on a hard drive, which can in turn severely impact performance.
TLB (Translation Lookaside Buffer)
A CPU cache used to hold page table entries.
TSO (TCP Segmentation Offload)
A feature of some NICs that offloads the packetization of data from the CPU to the NIC. TSO is supported
by the E1000, Enhanced VMXNET, and VMXNET3 virtual network adapters (but not by the normal
VMXNET adapter).
U Uniprocessor (UP)
A single-processor architecture. See also Symmetric Multiprocessor (SMP).
V Vanderpool
A code name for Intel’s version of virtualization assist, included in some 64-bit Intel processors. See
Virtualization Technology.
Virtual CPU (vCPU)
A processor within a virtual machine. ESX 4.0 currently supports up to eight virtual CPUs per virtual
machine.
Virtual Disk
A virtual disk is a file or set of files that appears as a physical disk drive to a guest operating system. These
files can be on the host machine or on a remote file system. When you configure a virtual machine with a
virtual disk, you can install a new operating system into the disk file without the need to repartition a
physical disk or reboot the host.
Virtual Machine
A virtualized x86 PC environment in which a guest operating system and associated application software
can run. Multiple virtual machines can operate on the same host system concurrently.
Virtual SMP
A VMware proprietary technology that supports multiple virtual CPUs in a single virtual machine.
Virtual Switch (vSwitch)
A software equivalent to a traditional network switch.
Virtualization Assist
A general term for technology included in some 64-bit processors from AMD and Intel that can allow
64-bit operating systems to be run in virtual machines (where supported by VMware Workstation). More
information is available in VMware knowledge base article 1901. See also AMD Virtualization and
Virtualization Technology.
Virtualization Overhead
The cost difference between running an application within a virtual machine and running the same
application natively. Since running in a virtual machine requires an extra layer of software, there is by
necessity an associated cost. This cost may be additional resource utilization or decreased performance.
Virtualization Technology (VT)
Intel’s version of virtualization assist, included in some 64-bit Intel processors. See also Virtualization
Assist.