I think you may be talking about compacting the registry (not compressing). The registry is constantly growing as new software is installed and additional entries made for all sorts of other reasons. Compacting the registry tidies it up, removing outdated clutter and tidying it up whic can reduce its size a little and also speed up access. Neither improvement is likely to make any difference observable to the human eye but I generally do some tidying up now and again if only for the sake of that - keeping things tidy. You can to the job using Ccleaner, a well established program free from here:
Thanks a lot for clearing that up,i was not aware that ccleaner could do the job,i have ccleaner installed and i use it every day(i am a cleaning freak)again thanks a lot,people on this forum has been so nice and helpfull.Kind Regards casi