VMware vSphere Architectures Compared

vSphere ESX Architecture

In the original VMware® ESX® architecture, the virtualization kernel (referred to as the VMkernel) was augmented with a management partition known as the console operating system (COS or service console). The primary purpose of the COS was to provide a management interface into the host. Various VMware management agents were deployed in the COS, along with other infrastructure service agents (e.g. name service, time service, logging, etc). In this architecture, many customers deployed other agents from third parties to provide particular functionality, such as hardware monitoring and system management. Furthermore, individual admin users logged into the COS to run configuration and diagnostic commands and scripts.

New vSphere ESXi Architecture

In the new VMware vSphere® ESXi™ architecture, the COS has been removed and all of the VMware agents run directly on the VMkernel. Infrastructure services are provided natively through modules included with the VMkernel. Other authorized third-party modules, such as hardware drivers and hardware monitoring components, can run in VMkernel as well. Only modules that have been digitally signed by VMware are allowed on the system, creating a tightly locked-down architecture. Preventing arbitrary code from running on the VMware vSphere® host greatly improves the security of the system.

Architectures Compared

The vSphere Hypervisor Architecture

Learn how vSphere’s innovative architecture operates independently from any general-purpose operating system, offering improved security, increased reliability, and simplified management.


  • VMware and third-party agents run in the COS.
  • Most management functionality provided by agents running in the COS.
  • Users log into COS in order to run commands for configuration and diagnostics.


  • VMware agents run directly on VMkernel.
  • Authorized third-party modules can also run in VMkernel. These provide specific functionality.
    • Hardware monitoring.
    • Hardware drivers.
  • VMware components and third-party components updated independently.
  • The “dual-image” approach lets you revert to prior image if desired.
  • No arbitrary code is allowed on the system.

Comparing the Legacy and New vSphere Architectures

Comparing the previous generation ESX architecture with the new innovative ESXi architecture:

Capability ESX ESXi 5.x
Service Console Present Removed
Admin/config CLIs COS + vCLI PowerCLI + vCLI (enhanced)
Advanced Troubleshooting COS ESXi Shell
Scripted Installation Supported Supported
Boot from SAN Supported Supported
SNMP Supported Supported
Active Directory Integrated Integrated
HW Monitoring Third-party agents in COS CIM providers
Serial Port Connectivity Supported Supported
Jumbo Frames Supported Supported
Rapid deployment and central management of hosts via Auto Deploy Not Supported Supported
Custom image creation and management Not Supported Supported
Secure syslog Not Supported Supported
Management interface firewall Supported Supported

See the KB article for a detailed comparison.