But even without multi-threading, mold is still faster than other linkers. I can think of various reasons why, but I don't know which attributes how much. I believe the biggest contributor is its efficient data structure -- it is hard to make program faster by writing fast code, but it can naturally be achieved by designing efficient data structures. That said, it is hard to compare two or more programs to find out why one program is faster than the others unless their designs are similar.