VM's Maximum

An overview comparison from all vSphere Versions is available here.

Types	ESXI  4.1	ESXI 5	ESXI 5.1	ESXI 5.5
Released date	Jul-10	Aug-11	Sep-12	Sep-13
Hypervisor	ESX /ESXI	ESXi	ESXI	ESXi
Mx VM per host	320	512
Physical CPU per host	160	160	160	320
Physical Ram Per host	1 TB	2TB	2TB	4TB
VMDK size			2 TB	62 TB
Luns per host	256	256	256	256
Single Signon	NO	NO	SSO 1.0 built on identity management by RSA	SSO 5.5 completely rewritten from the ground up. Supports a multi-master mode
Powered on VM per Vcenter	10000	10000	10000	10000
Registered VM's per vcenter		15000	15000	15000
VM hw version	7	8	9	10
Max CPU per VM	8	32	64	64
Max Ram per VM	255GB	1TB	1TB	1TB
VM swap file size	255GB	1TB	1TB	1TB
VM tools version	8.3	8.6	9	9.4
VMFS version	VMF 3	VMF 3 & VMFS 5	VMFS 5	VMFS 5
VMFS Blcok size	1/2/4/8 MB	1/2/4/8 MB	1 MB	1 MB
HA Agent	AAM	FDM	FDM	FDM
HA host Approach	Primary & Secondary	Master & Slave	Master & Slave	Master & Slave
HA Failure Detection	Management N/W	Management N/w & Datastore	Management N/w & Datastore	Management N/w & Datastore
Storage DRS	NO	Yes	Yes	Yes
Auto deploy	NO	Yes	Yes	Yes
Storage Vmotion	Move VM files by block size	Move the VM file by IO Mirroring	Move the VM file by IO Mirroring	Move the VM file by IO Mirroring
VSAN	NO	No	NO	YES
Features	Boot from SAN Scripted Installation Storage I/O Control DRS Host Affinity Memory Compression Array Integration Network I/O Control	Auto Deploy Storage DRS vSphere Storage Appliance Profile driven storage vSphere Web Client vCenter Server Appliance ESXi Firewall	Single Sign-On Enhanced vMotion Sparse Virtual Disks Single-root I/O Virtualization vSphere Replication vSphere Data Protection vShield Endpoint	vSphere Flash Read Cache Virtual SAN Reliable Memory Technology vSphere Big Data Extensions vCenter Single Sign-On 2.0 vSphere App HA 40GBps NIC Support