VMware architecture Essentials !!

Since VMware vSphere 4.1 and its subsequent update and patch releases are the last releases to include both ESX and ESXi hypervisor architectures & future major releases of VMware vSphere will include only the VMware ESXi architecture, it is important to understand the differences between the conventional ESX and the lean ESXi virtualization products from VMware.

Difference between the VMware ESX and ESXi 4.1

Capability	VMware ESX	VMware ESXi
Service Console	Service Console is a standard Linux environment through which a user has privileged access to the VMware ESX kernel. This Linux-based privileged access allows you to manage your environment by installing agents and drivers and executing scripts and other Linux-environment code.	VMware ESXi is designed to make the server a computing appliance. Accordingly, VMware ESXi behaves more like firmware than traditional software. VMware has created APIs through which monitoring and management tasks – traditionally done through Service Console agents – can be performed. VMware has provided remote scripting environments such as vCLI and PowerCLI to allow the remote execution of scripts and commands. Tech Support Mode (TSM) provides a command-line interface that can be used by the administrator to troubleshoot and correct abnormal conditions on VMware ESXi hosts.
CLI-Based Configuration	VMware ESX Service Console has a host CLI through which VMware ESX can be configured. VMware ESX can also be configured using vSphere CLI (vCLI) or vSphere PowerCLI.	The vSphere CLI (vCLI) is a remote scripting environment that interacts with VMware ESXi hosts to enable host configuration through scripts or specific commands. It replicates nearly all the equivalent COS commands for configuring ESX. VMware vSphere PowerCLI is a robust command-line tool for automathing all aspect of vSphere management, including host, network, storage, virtual machine, guest operating system, and more. Note: vCLI, PowerCLI, and vSphere SDk for Perl are limited to read-only access for the free vSphere Hypervisor edition. To enable full functionality of vCLI on a VMware ESXi host, the host must be licensed with vSphere Essentials, vSphere Essential Plus, vSphere Standard, vSphere Advanced, vSphere Enterprise, or vSphere Enterprise Plus. Certain COS commands have not been implemented in the vCLI because they pertain to the management of the COS itself and not ESXi.
Scriptable Installation	VMware ESX supports scriptable installations through utilities like KickStart.	VMware ESXi supports scriptable installations using a mechanism similar to Kickstart, and includes the ability to run pre- and post-installation scripts. VMware ESXi also provides support for post installation configuration using PowerCLI- and vCLI-based configuration scripts.
Boot from SAN	VMware ESX supports boot from SAN. Booting from SAN requires one dedicated LUN per server.	VMware ESXi may be booted from SAN. This is supported for Fibre Channel SAN, as well as iSCSI and FCoE for certain storage adapters that have been qualified for this capability.
Serial Cable Connectivity	VMware ESX supports interaction through direct-attached serial cable to the VMware ESX host.	VMware ESXi does not support interaction through direct-attached serial cable to the VMware ESXi host at this time.
SNMP	VMware ESX supports SNMP.	VMware ESXi supports SNMP when licensed with vSphere Essentials, vSphere Essential Plus, vSphere Standard, vSphere Advanced, vSphere Enterprise, or vSphere Enterprise Plus. The free vSphere Hypervisor edition does not support SNMP.
Active Directory Integration	VMware ESX provides native support for Active Directory integration.	VMware ESXi provides native support for Active Directory integration.
HW Instrumentation	Service Console agents provide a range of HW instrumentation on VMware ESX.	VMware ESXi provides HW instrumentation through CIM Providers. Standards-based CIM Providers are distributed with all versions of VMware ESXi. VMware partners include their own proprietary CIM Providers in customized versions of VMware ESXi. These customized versions are available either from VMware’s web site or the partner’s web site, depending on the partner. Remote console applications like Dell DRAC, HP iLO, IBM RSA, and FSC iRMC S2are supported with ESXi.
Software Patches and Updates	VMware ESX software patches and upgrades behave like traditional Linux based patches and upgrades. The installation of asoftware patch or upgrade may require multiple system boots as the patch or upgrade may have dependencies on previous patches or upgrades.	VMware ESXi patches and updates behave like firmware patches and updates. Any given patch or update is all-inclusive of previous patches and updates. That is, installing patch version “n” includes all updates included in patch versions n-1, n-2, and so forth. Furthermore, third party components such as OEM CIM providers can be updated independently of the base ESXi component, and vice versa.
vSphere Web Access	vSphere Web Access is only experimentally supported in VMware ESX.	VMware ESXi does not support web access at this time.
Diagnostics and Troubleshooting	VMware ESX Service Console can be used to issue command that can help diagnose and repair support issues with the server.	VMware ESXi has several ways to enable support of the product: Remote command sets such as the vCLI include diagnostic commands such as vmkfstools, resxtop, and vmware-cmd. The console interface of VMware ESXi (known as the DCUI or Direct Console User Interface) has functionality to help repair the system, including restarting of all management agents. Tech Support Mode, which allows low-level access to the system so that advanced diagnostic commands can be issues.
Jumbo Frames	VMware ESX 4.1 fully supports Jumbo Frames.	VMware ESXi 4.1 fully supports Jumbo Frames.