what is the max vCPU limit on windows 2008 R2 STD, ENT, ENT plus in vSphere 5.5.
In VM i have increased the virtual sockets to 8 and cores to 1, from OS end i can see only 4 processor.
In this case you are most likely using the Standard Edition of Windows Server 2008 R2, which is limited to 4 sockets. The is a limitation in Windows rather than vSphere. What you can do however, is to configure a lower number of virtual multi-core vCPUs.
André
... here's a nice Technet blog post regarding the Windows Server CPU support: http://blogs.technet.com/b/matthts/archive/2012/10/14/windows-server-sockets-logical-processors-symmetric-multi-threading.aspx
This link talks about Hyper-v, but we are using vSphere 5.5.
Don't get confused with the "... with Hyper-V Enabled" addition for the mentioned server versions. What matters is the number of supported sockets for Windows itself. This is independent of whether or not the Hyper-V role is enabled.