how to use hdd as a ram if speed is not a constraint

i want to use hdd as RAM & permanent storage to install new application entirely inside an external HDD which can be plugged in and that application can be ran and once finished using it just plug out.

i am fascinated with idea of using appx 500 gb external hdd as a kind of storage of thousands of installed applications.

please give your valuable advise on, if this is feasible. i am not worrying about i/o read & seek time at this point of time.