Why not footage and os on the same drive?

An EXAMPLE concerning trying to use only ONE Hard Drive for Video Editing... this was written for spinning platter drives, so an SSD will be better since there is no physical read/write head to move... I do not know how MUCH better, so I built my computer with 4 SSD drives for maximum speed
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You are a music conductor, with a baton that you use to point to various parts of the orchestra... this is like the operating system pointing to various parts of the hard drive to do file housekeeping or to load program segments for various functions
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Now, at the same time and with the same hand... while still using the baton to conduct the orchestra... pick up a bow and play a fiddle... this would be doing something with your video file at the same time as all the other work
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You as a person cannot do both at the same time with the same hand
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A computer is a LITTLE better, in that it can switch from one kind of task to another very quickly... but not quickly enough for EASY video editing
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You need AT LEAST two hard drives (separate drives, never a partition on one drive) with Windows (or Mac OS) and software on your boot drive, and video files on a 2nd drive so the boot drive is not slowed down by trying to do everything