Ignoramus633 wrote:
Is it possible to use a regular compressor as a vacuum pump? After
all, both do the same, pump air out of some place and into another
place.

Yes but the dead space above the piston (ie, the part of the cylinder
which isn't swept) limits the ultimate vacuum quite badly. Oil-sealed
rotary vane pumps don't suffer from this limitation; their ultimate
vacuum is usually limited by the vapour pressure of the oil.

Chris