Introduction:
Non-volatile memory refers to a type of computer memory that retains its data even when the power is turned off. It allows for persistent storage of information and is crucial in various computing applications. There are several early forms of non-volatile memory, but in this case, the correct answer is magnetic core memory.

Explanation:
Magnetic core memory, also known as ferrite core memory, was one of the earliest forms of non-volatile memory. It was widely used in early computers during the 1950s and 1960s. Let's explore the characteristics and working principle of magnetic core memory:

1. Structure:
Magnetic core memory consisted of a grid of tiny magnetic cores made of ferrite material. Each core represented a single bit of data, which could be magnetized in two directions, corresponding to binary values of 0 and 1.

2. Working Principle:
When a current passed through a wire threaded through a core, the magnetic field of the current could magnetize the core in one direction. This represented a binary value of 1. If no current passed through the wire, the core retained its previous magnetization, representing a binary value of 0.

3. Non-Volatility:
The key characteristic of magnetic core memory that made it non-volatile was its ability to retain data even when the power was turned off. This was because the magnetization of the cores was maintained by the magnetic properties of the ferrite material, requiring no ongoing power supply.

4. Read and Write Operations:
To read data from a specific memory location, a sense wire was passed through the corresponding core. The change in magnetic flux induced a voltage in the sense wire, indicating the stored binary value. Writing data involved selectively applying currents to the appropriate wires to magnetize the desired cores.

5. Advantages and Disadvantages:
Magnetic core memory had several advantages, including its non-volatile nature, high reliability, and fast access times. However, it also had limitations such as low storage density, high cost, and limited scalability.

Conclusion:
In summary, magnetic core memory was an early form of non-volatile memory that utilized magnetic properties to store and retain data. It played a significant role in the development of early computers and paved the way for subsequent advancements in non-volatile memory technologies.