VMware ESX and ESXi

Service Console


The core of the vSphere product suite is the hypervisor, which is the virtualization layer that serves as the foundation for the rest of the product line. In vSphere, the hypervisor comes in two different forms: VMware ESX and VMware ESXi. Both of these products share the same core virtualization engine, both can support the same set of virtualization features, and

both are considered bare-metal installations. VMware ESX and ESXi differ in how they are packaged.

VMware ESX consists of two components that interact with each other to provide a dynamic and robust virtualization environment: the Service Console and the VMkernel. The Service Console, for all intents and purposes, is the operating system used to interact with VMware ESX and the virtual machines that run on the server. The Linux-derived Service Console includes services found in traditional operating systems, such as a firewall, Simple Network Management Protocol (SNMP) agents, and a web server. At the same time, the Service Console lacks many of the features and benefits that traditional operating systems offer. This is not a deficiency, though. In this particular case, the Service Console has been intentionally stripped down to include only those services necessary to support virtualization, making the Service Console a lean, mean virtualization machine.

The second installed component is the VMkernel. While the Service Console gives you access to the VMkernel, the VMkernel is the real foundation of the virtualization process. The VMkernel manages the virtual machines' access to the underlying physical hardware by providing CPU scheduling, memory management, and virtual switch data processing. Figure 1.1 shows the structure of VMware ESX.

VMware ESXi, on the other hand, is the next generation of the VMware virtualization foundation. Unlike VMware ESX, ESXi installs and runs without the Service Console. This gives ESXi an ultra light footprint of only 32MB. ESXi shares the same underlying VMkernel as VMware ESX and supports the same set of virtualization features, but it does not rely upon the Service Console.

Compared to previous versions of ESX/ESXi, VMware has expanded the limits of what the hypervisor is capable of supporting. Table 1.1 shows the configuration maximums for this version of ESX/ESXi as compared to the previous release.


VMWARE ESX 4 Maximum


Number of virtual CPUs per host



Number of cores per host



Number of logical CPUs



(hyperthleading enabled)

Number of virtual CPUs per core


8 (increased to 20 in Update 3)

Amotmt of RAM per host


128GB (increased to 256GB In Update 3)