Magnetic core memory, an early form of computer memory, stores digital information using tiny magnetic rings or cores. Each core can be magnetized in one of two directions to represent binary data. Here’s a detailed breakdown of how it works:
### Structure and Components
1. **Magnetic Cores**: These are small, toroidal (doughnut-shaped) pieces of magnetic material, typically made from ferrite. Each core can be magnetized in one of two directions.
2. **Wires**: Cores are arranged in a grid-like pattern. There are two sets of orthogonal (perpendicular) wire grids—one set for rows and one set for columns. These wires are threaded through each core in the grid.
3. **Select and Sense Lines**: To access or change the data, specific rows and columns of the grid are selected. This involves sending electrical signals through the corresponding wires.
### Storing Information
1. **Magnetization**: Each core can be magnetized in one of two directions. This direction of magnetization represents binary data:
- **North-South Magnetization**: Represents a binary `0`.
- **East-West Magnetization**: Represents a binary `1`.
The core's magnetization direction is stable and persists until it is changed by an external signal.
2. **Writing Data**: To write data to a specific core:
- Select the row and column corresponding to the core you want to modify.
- Pass current through the row and column wires. The resulting magnetic field will change the magnetization direction of the core at their intersection.
3. **Reading Data**: To read data:
- Again, select the specific row and column.
- Pass a small sensing current through the selected row or column.
- If the core has been magnetized in one direction, it will induce a voltage in the sense line when the current is passed, indicating a `0`. If the core has been magnetized in the opposite direction, it will induce a different voltage, indicating a `1`.
### Advantages and Drawbacks
- **Advantages**:
- **Non-Volatility**: Data remains stored even when power is lost.
- **Reliability**: Magnetic cores are durable and less susceptible to physical damage compared to other early storage mediums.
- **Drawbacks**:
- **Size**: Magnetic core memory takes up more physical space compared to modern semiconductor memory.
- **Speed**: It is slower compared to contemporary memory technologies like RAM and SSDs.
### Historical Context
Magnetic core memory was widely used in the mid-20th century, notably in early computers like the IBM 701 and the Apollo Guidance Computer. It was eventually replaced by semiconductor memory technologies, which are faster and more compact.
In summary, magnetic core memory stores digital information through the magnetic orientation of tiny cores. Data is written and read by selecting specific cores using magnetic fields and electrical currents, making it a fascinating example of early data storage technology.