which edition of windows 7 have bit drive encryption feature
According to a Wikipeida entry at:
http://en.wikipedia.org/wiki/BitLocker_Drive_Encryption
"BitLocker Drive Encryption is a full disk encryption feature included
with the Ultimate and Enterprise editions of Microsoft's Windows Vista
and Windows 7 desktop operating systems, as well as the Windows Server
2008 and Windows Server 2008 R2 server platforms."
And according to Microsoft TechNet at:
http://technet.microsoft.com/en-us/library/ee449438(WS.10).aspx#BKMK_HSRequirements
"Operating system
Windows 7 Ultimate, Windows 7 Enterprise, or Windows Server 2008 R2."
So it looks like the answer to your question is Windows 7 Ultimate and
Enterprise editions are the two versions of Windows 7 that are designed
for BitLocker use.