Datasheet

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CHAPTER 1 INTRODUCING VMWARE VSPHERE 5

Type 1 and Type 2 Hypervisors

Hypervisors are generally grouped into two classes: type 1 hypervisors and type 2 hypervisors. Type

1 hypervisors run directly on the system hardware and thus are often referred to as bare-metal hyper-

visors. Type 2 hypervisors require a host operating system, and the host operating system provides

I/O device support and memory management. VMware ESXi is a type 1 bare-metal hypervisor. (In

earlier versions of vSphere, VMware ESX was also considered a type 1 bare-metal hypervisor.) Other

type 1 bare-metal hypervisors include Microsoft Hyper-V and products based on the open source

Xen hypervisor like Citrix XenServer and Oracle VM.

VMware ESXi, on the other hand, is the next generation of the VMware virtualization foun-

dation. Unlike VMware ESX, ESXi installs and runs without the Linux-based Service Console.

This gives ESXi an ultralight footprint of approximately 70 MB. Despite the lack of the Service

Console, ESXi provides all the same virtualization features that VMware ESX supported in ear-

lier versions. Of course, ESXi 5 has been enhanced from earlier versions to support even more

functionality, as you’ll see in this chapter and in future chapters.

The key reason that VMware ESXi is able to support the same extensive set of virtualization

functionality as VMware ESX without the Service Console is that the core of the virtualization

functionality wasn’t (and still isn’t) found in the Service Console. It’s the VMkernel that is the

foundation of the virtualization process. It’s the VMkernel that manages the VMs’ 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 ESXi.

Figure 1.1

The VMkernel is the

foundation of the

virtualization

functionality found

in VMware ESXi.

VMkernel

I mentioned earlier that VMware ESXi 5 is enhanced over earlier releases. One such area of

enhancement is in the limits of what the hypervisor is capable of supporting. Table 1.2 shows the

conﬁ guration maximums for the last few versions of VMware ESX/ESXi.

These are just some of the conﬁ guration maximums. Where appropriate, future chapters will

include additional values for VMware ESXi maximums for network interface cards (NICs), stor-

age, VMs and so forth.

Given that VMware ESXi is the foundation of virtualization within the vSphere product

suite, you’ll see content for VMware ESXi throughout the book. Table 1.1, earlier in this

section, tells you where you can ﬁ nd more information about speciﬁ c features of VMware

ESXi elsewhere in the book.

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