Re: "in some apps"?
I had a PDT-11/150 running RT-11 on a pair of 8" floppies. Actually I still have it but it won't boot, the power supply capacitors probably having dried up. Might be fun for a paleocomputer geek. RT-11 was the predecessor (i.e., what they tried to copy) of CP/M and QDOS/PC-DOS/MS-DOS.