The 90nm lithography machine and 28nm lithography machine differ by 3 generations. Algebra refers to the advancement of the chip manufacturing process, with each generation representing a new generation of technology and smaller manufacturing sizes. 90nm represents a manufacturing size of 90 nanometers, while 28nm represents a manufacturing size of 28 nanometers. Therefore, the 28nm lithography machine is more advanced than the 90nm lithography machine, with higher resolution and higher integration.