Decades ago, sewing machines came in an immovable form, but nowadays they are portable and the pedal is connected to the power socket. For mechanical sewing machines you must select the stitch, and the length and width manually. They can be regulated by levers or dials, depending on how old they are.
The electronic machines, on the other hand, select the stitch, as well as its length and width, with buttons. They are digital machines, with a variety of programs, and usually include an LCD screen so you can see your selection. They are more accurate and generally include Overlock or even Festoon stitches. They are more efficient but also more expensive.