In this blog post, I’ll explain the difference between analog and digital, as well as how hard drives store and read data, in an easy-to-understand way.

The Difference Between Digital and Analog

Just looking at them evokes a strong sense of nostalgia: LP records, videotapes crammed into the cabinet under the TV, and dozens of encyclopedias that made you feel smarter just by having them on your bookshelf. Nowadays, it’s hard to even find these items. Before we knew it, they began to be stored inside a computer in the corner of a room—more precisely, inside a hard disk drive capable of holding tens of thousands of times more data in the same physical space. However, this hard disk drive does more than just store large amounts of data; the very method of storing information is completely different. That is precisely what makes it a “digital” storage medium.
What exactly does the term “digital” mean? And how exactly does a hard drive handle information? If we consider the difference between analog and digital methods, analog refers to continuous quantities or values, while digital refers to discrete quantities or values. For example, a thermometer with a red mercury column rising is analog, whereas a thermometer displaying a temperature as a number, such as 37.5°C, is digital.
From the perspective of storage media, analog media either store the original information as-is or convert it into a continuous signal that corresponds to the original information in its entirety. In contrast, digital storage media, such as hard disks, divide the original information into a series of discrete values according to predetermined rules and store those values. If the analog method is like a drawing that copies the original exactly, the digital method can be likened to a highly intricate mosaic.
Let’s take a closer look at how digital information is represented by considering a very simple digital system. Imagine a sunset sky tinged with red. In this system, let’s assume we recognize only four distinct colors: red, crimson, orange, and yellow. Divide the entire sky into one hundred sections and classify the color of each section using the four colors mentioned above. Now, the landscape in our imagination is no longer a continuous sky, but rather one hundred sections divided into red, crimson, orange, and yellow hues. This is what “digital” means.
Because digital information is discrete, each color can be mapped to a number. In particular, we map these to binary numbers, because in the physical world, the two states that can be most clearly distinguished are “present” and “absent,” or “original state” and “opposite state”—that is, 0 and 1. So, for example, we agree to represent red as “00,” crimson as “01,” orange as “10,” and yellow as “11.” If we erase each section and fill them with ‘00’, ‘01’, ‘10’, and ‘11’, the digitization of the information is complete.
If we were to use hundreds of colors instead of four, and millions of sections instead of a hundred, the digitized information would capture an image very similar to the original sky.
So how can we tell what kind of information this sequence of ‘0’s and ‘1’s represents—for example, whether it’s an image or sound? The answer is simple: we label the information. In other words, we also express and store information such as ‘the following 0’s and 1’s represent image data’ or ‘the image data has now ended’ using 0’s and 1’s. For example, if a system uses ‘1101’ to indicate image data and ‘1111’ to indicate the end of the data, the final digital information would look like this: ‘1101…a sequence of 0s and 1s representing image data…1111’.
This method is possible because, when designing a digital information system, the pattern of 0s and 1s representing the identifier is structured so that it does not overlap with the pattern representing the information itself. The hard disk inside a computer stores digitized information in exactly this way.

The Principles of Hard Disk Storage and Reading

Now let’s examine how a hard disk actually uses 0s and 1s—that is, binary numbers—to store and retrieve information. A hard disk drive consists of two main parts: the head, which is the device that stores and reads information, and the platter, which is the space where the information is actually stored.
The head is a device that utilizes Ampère’s law. Ampère’s law states that when an electric current flows through a material in a specific direction, a magnetic field is generated around it; conversely, if a magnet is present, a current flows in a specific direction depending on the magnet’s orientation. Every time the direction of the current changes, the polarity of the head reverses. In other words, the head functions like a large magnet that can instantly change its polarity by controlling the direction of the current.
The platter is a circular storage space with tiny magnets scattered across its surface, designed to store the momentary magnetic signals generated by the head, whose polarity can be freely controlled. A hard disk stores information by rotating the platter beneath the head so that, as a portion of it passes beneath the head, the small magnets on the platter align in a specific direction under the influence of the head’s magnet.
This process is similar to printing a lithograph. Just as the opposite image of the master plate is printed on paper, the small magnets on the platter align in the opposite direction of the magnet appearing on the head. This is because the north pole of a magnet is attracted to the south pole, and the south pole is attracted to the north pole. As a result, the tiny magnets on the platter align so that either the north or south poles face a specific direction. Assuming a specific direction is “up,” a north pole facing up represents “0,” and a south pole facing up represents “1,” allowing for the representation of binary numbers.
The process by which a hard disk reads this written information is the reverse of the storage process. If the platter is passed under the head while the current flowing through the head magnet is turned off, the poles of the head magnet are aligned by the platter’s magnets, and according to Ampère’s law, a current flows in the same direction as when the data was stored. By reading this current, we can determine what information was stored—that is, which 0s and 1s were present.
With the dramatic advancement in the performance of digital storage media—such as hard disks, flash memory (USB drives), and optical discs—as well as digital information processing devices like computers, most of the information around us is now stored and processed in digital form. All digital information is represented by 0s and 1s. Thanks to this, digital information possesses universality, meaning it can be stored and exchanged in the same way regardless of its type or volume.
Because of this, we are now living in an unprecedented age of information abundance. At this juncture, I hope this article, though brief, serves as a simple answer to the question, “What is digital?”