VMware ESX and VMware ESXi are both bare-metal hypervisor architectures that install directly on the server hardware. Both provide industry-leading performance and scalability; the difference resides in the architecture components and the operational management of VMware ESXi. Although neither hypervisor architectures relies on an OS for resource management, VMware ESX relies on a Linux operating system, called the service console, to perform two management functions: executing scripts and installing third party agents for hardware monitoring, backup or systems management. The service console has been removed from ESXi, drastically reducing the hypervisor footprint and completing the ongoing trend of migrating management functionality from the local command line interface to remote management tools. The smaller code base of ESXi represents a smaller “attack surface” and less code to patch, improving reliability and security. The functionally of the service console is replaced by remote command line interfaces and adherence to system management standards. View a detailed comparison of VMware ESX and VMware ESXi management.

Starting with VMware vSphere 5, ESXi is only hypervisor option available to deploy vSphere. VMware ESXi’s smaller code base and lack of reliance on a general purpose operating system make it the more reliable and secure choice. Its compact design allows it to be embedded in mainstream physical servers for simpler and faster deployments. VMware ESXi was also designed with simplicity in mind. Its menu-driven startup and automatic configurations make it the easiest way to get started with VMware virtualization.

VMware recommends that customers migrate existing ESX deployment to ESXi when upgrading to vSphere 5 or vSphere 4.1.Before migrating you should consider the following points before deploying ESXi or switching from ESX to ESXi:

• Make sure your hardware is supported on ESXi as the hardware compatibility list (HCL) is not identical to ESX. In general, VMware ESX has a larger HCL due to its support for legacy servers but expect support parity for ESXi and ESX on all new servers.
• Make sure that your third party management and back up tools are compatible with ESXi. Some of these tools have a dependency on the service console (COS) of ESX, which has been removed from the architecture of ESXi. VMware has developed alternative integration points for ESXi and is actively engaged with backup and management partners to help them make the transition from ESX to ESXi. Most major management or backup vendors such as IBM, BMC, CA, HP, EMC, Symantec and Veritas offer ESXi-compatible products but you should check with your third party vendor for the latest information on supported products and version numbers. Read this KB article for a detailed comparison of VMware ESXi and VMware ESX management.

VMware will continue to provide technical support for VMware ESX according to the VMware vSphere support policy.

The VMware ESXi hypervisor architecture is certified on over 1000 server systems and can run off certified USB keys on certain models. In general, new hardware systems supported for ESX will also be supported for ESXi, but please search the hardware compatibility lists (HCLs) for information about a specific hardware system.

VMware offers the broadest operating system support as compared to any other virtualization vendor. VMware ESXi and ESX have virtually the same guest operating system support. Please search the guest operating system compatibility list for a full list of supported guest operating systems.

Yes. You can use the free VMware vCenter Converter to import virtual machines that were created using VMware Server, Microsoft Virtual Server, or Microsoft Virtual PC version 7 or higher. VMware vCenter Converter also supports conversions from sources such as physical machines and certain third party disk image formats. View the VMware vCenter Converter FAQs for further details.

ESXi is VMware’s most advanced bare metal hypervisor architecture. It is the only hypervisor architecture available with vSphere 5 or later. Customers install the ESXi software on a physical sever to virtualize its resources (CPU, memory, etc.) and share them among virtual machines. Applying vSphere licenses (Essentials, Essentials Plus, Standard, Enterprise, Enterprise Plus) transforms a collection of individual logically separate ESXi hosts into a pool of virtualized resources that can be dynamically allocated to virtual machines. vSphere licenses also allow customers to take advantage of features such as vMotion, DRS, HA, etc.

VMware vSphere Hypervisor is the entry level edition of VMware vSphere. It is available at no cost in order to help companies of all sizes experience the fundamental benefits of virtualization. VMware vSphere Hypervisor enables customers to consolidate physical servers running multiple virtual machines to a single vSphere host. VMware vSphere Hypervisor is ideal for IT professionals to become familiar with virtualization technology and prove its value in their own organizations. In addition to server consolidation capabilities, the VMware vSphere editions available for purchase (Essentials, Essentials Plus, Standard, Enterprise, Enterprise Plus) offer more advanced capabilities, such as high availability, live migration, power management, automatic load balancing and much more. To unlock such capabilities customers need to purchase the corresponding VMware vSphere license and deploy VMware vCenter Server management software which enables centralized management of multiple vSphere hosts.

The simplest way to evaluate the VMware ESXi architecture is to download and install vSphere Hypervisor. Alternatively you can leverage the vSphere evaluations

VMware vCenter Update Manager will update ESXi An update utility is also provided for environments where VMware Update Manager is not present.

Note:VMware vCenter Update Manager is not available for the free VMware vSphere Hypervisor.