Magnetic moment of current loop From what I have learnt, the magnetic moment of a current carrying loop is
$$\pmb{\mu} = NI \mathbf{A}.$$
But what is written in this book Modern atomic and nuclear physics by Fuzia Yang, I am not able to understand.

4.1.1 Classical Expression
It is well known in classical electromagnetism that the mangetic moment $\mu$ associated with a small electric current may be expressed as (see Fig. 4.1(a))
$$\pmb{\mu} = \frac{i}{c} S \mathbf{n}_0$$
where $i$ is the electric current in the sense of positive charge flow, $c$ is the speed of light ($c=1$ in this equation in "reduced" units based on the SI system of units), $S$ is the area enclosed by the current circuit, and $\mathbf{n}_0$ is a unit vector normal to the plane of the circuit.

It would be great help if somebody could provide a clue for how the two are connected.
 A: 
From what I have learnt, the magnetic moment of a current carrying loop is
$$\pmb{\mu} = NI \mathbf{A}.$$


But what is written in this book Modern atomic and nuclear physics by Fuzia Yang, I am not able to understand.
4.1.1 Classical Expression

It is well known in classical electromagnetism that the mangetic moment $\mu$ associated with a small electric current may be expressed as (see Fig. 4.1(a))
$$\pmb{\mu} = \frac{i}{c} S \mathbf{n}_0$$
where $i$ is the electric current in the sense of positive charge flow, $c$ is the speed of light ($c=1$ in this equation in "reduced" units based on the SI system of units), $S$ is the area enclosed by the current circuit, and $\mathbf{n}_0$ is a unit vector normal to the plane of the circuit.


He is just using different symbols and considering only one loop winding (not $N$ windings). He is also using different units and, as he writes, you can set $c$ to 1 to convert to "reduced" SI units.
The translation of symbols from the bottom equation to the top equation is:
$$
S\mathbf n_0 \to \mathbf A
$$
$$
i \to I
$$
$$
c \to 1
$$
