vSphere 5.1 (ESXi 5.1) can run any hardware level since ESX Server 3.5

Last year, I missed this tiny sentence:

So in plain English, any VM that was generated on VMware ESX Server 3.5 or later can run atop ESXi 5.1 unchanged.

Which means it is a snap to move your VMs from older ESX / ESXi / vSphere versions as long as they are ESX 3.x or later.

In fact hardware version 7 has the widest compatibility amongst ESX/ESXi/vSphere/Fusion/Workstation/Player versions (see the table at the bottom).

The free version still has a 32 gigabyte physical RAM limit (people are still confused by the vRAM / Physical RAM distinction, especially since vRAM is not limited any more).

It was indeed in the vSphere 5.1 Release Notes:

Virtual machines that are compatible with ESX 3.x and later (hardware version 4) are supported with ESXi 5.1. Virtual machines that are compatible with ESX 2.x and later (hardware version 3) are no longer supported.

and the vSphere 5.0 Release Notes:

Virtual machines with virtual hardware versions 4.0 and later are supported with ESXi 5.0. Hardware version 3 is no longer supported. To use hardware version 3 virtual machines on ESXi 5.0, upgrade virtual hardware.

There is even this interesting table on ESXi/ESX/vSphere version/hardware version compatibility:

ESXi hosts and compatible virtual machine hardware versions are listed in this table:

Note: For VMware vCenter Server 5.1, virtual machines can only be created with hardware version 9 from the vSphere Web Client. However, you are able to upgrade to hardware version 9 using the vSphere Client.

ESXi/ESX version	Hardware version				Compatible with vCenter Server version
	Version 9	Version 8	Version 7	Version 4
ESXi 5.1	Create, Edit, Run	Create, Edit, Run	Create, Edit, Run	Edit, Run	vCenter Server 5.1
ESXi 5.0	Not Supported	Create, Edit, Run	Create, Edit, Run	Edit, Run	vCenter Server 5.0
ESXi/ESX 4.x	Not Supported	Not Supported	Create, Edit, Run	Create, Edit, Run	vCenter Server 4.x
ESX 3.x	Not Supported	Not Supported	Not Supported	Create, Edit, Run	vCenter Server 2.x and later

And this table on virtual hardware versions supported in various products (including VMware Fusion, Workstation and Player):

This table lists VMware products and their virtual hardware version:

Virtual Hardware Version	Products
9	ESXi 5.1 Fusion 5.x Workstation 9.x Player 5.x
8	ESXi 5.x Fusion 4.x Workstation 8.x Player 4.x
7	ESXi/ESX 4.x Fusion 3.x Fusion 2.x Workstation 7.x Workstation 6.5.x Player 3.x Server 2.x
6	Workstation 6.0.x
4	ACE 2.x ESX 3.x Fusion 1.x Player 2.x
3 and 4	ACE 1.x Lab Manager 2.x Player 1.x Server 1.x Workstation 5.x Workstation 4.x
3	ESX 2.x GSX Server 3.x

–jeroen

via:

• Free Download VMware vSphere Hypervisor (ESXi) 5.1
• VMware kills vRAM memory tax with vSphere 5.1 server virt • The Register.
• ESXi 5.1 Free with no vRAM limit but physical RAM limit of 32Gb.
• VMware Communities: ESXi 5.1 Free Version RAM limitation?.
• vSphere 5.1 Release Notes.
• vSphere 5.0 Release Notes.
• VMware KB: ESXi/ESX hosts and compatible virtual machine hardware versions in vSphere 5.x.
• VMware KB: Virtual machine hardware versions.