dllhell is a problem that we faced when we install any software then some time we lose our old version after install new version,  this problem is solved in .net with the use of Globel assemble case.

dllheavan is diffrent to dllhell in this we are able to install diffrent version in our computer

When we install a new application,the new version of a DLL overwrites the old version of that DLL ,which may cause an application which has been using the older version of the DLL to break. This is the DLL Hell.

(This may be not a problem if the newer version is backword compatible with the old version)

DLL heaven is the answer to the DLL Hell,which allows the old and new version of DLL to exit side-by-side.That is installation of a new versionof an already existing DLL without replacing the older one.

DDL HELL : here dll hell is that when we install new version of any software , the new version overwrites the old version . For example When we install MSWORD 2003 over 2000 it will replace MSWORD 2000 . It's a dll hell.

DDL heaven: it is just like both of the version run after installing new version .For example .net 1.0 and 2.0 both installed in ur syatem.