External hard drive question

Hi there I have a question that i would really appreciate if someone with more knowledge on the issue could answer

So I have a ps4 first gen 500gb and an xbox one s 500 gb I was wondering if I bought a 1tb external hard drive for the ps4 and took the external hard drive apart put the 1tb into the ps4 and used the ps4s hard drive as the external hard drive and use it on the xbox one s? Trying to get the most bang for my buck lol thanks!