What is the difference between an overlocker and a regular sewing machine?

Unfortunately, it is not possible to purchase a combined overlocker and sewing machine, like there was many years ago when the New Home Combi DX was around. Yes, there is a huge difference between an overlock and a sewing machine!

• Overlockers have loopers, cut fabric and use multiple needles to form a stitch.
  
  An overlocker (or serger) is designed to sew seams, trim excess fabric, and finish raw edges all at once, providing a professional, clean finish, especially for stretch or woven fabrics. It uses multiple threads and has a cutting blade, unlike a regular sewing machine.
  
  Compact, they can stitch very quickly at speeds up to 1500 stitches-per-minute.
  
  
• Sewing machines use only 2 threads and a single needle to manufacture or repair garments, or they can be used for embroidery, top stitching and decorative sewing.
  A sewing machine's primarily function is to stitch fabrics together but cannot trim fabric like an overlocker. Inserting a zip or sewing a buttonhole at speed is not possible without a sewing machine.
  Often, longer models offer plenty of sewing bed space to the right of the needle, are inclined to be heavier than a compact overlock machine.
  
  
• They both have their specialist techniques to add to your sewing room, and, personally, I would not be without either of them.