I am new to packaging technology. So can anyone please let me know what is legacy setup and it's disadvantages.
Thanks in advance
A legacy package is an application created as a setup.exe using non-msi based technology.
This can be tricky since sometimes you'll see vendors wrap their msi installs with a .exe that will make sure the windows installer engine is installed/working etc before installing. Others wrap msi's to chain multiple msi installs.
you'll hear them referenced as old wise or installshield packages as well.
Generally these can be some of the most difficult packages to automate with present day tools/scripts since they don't have silent install command lines or follow the traditional rules.
For present day your best to learn app virt techs and msi packaging.