This blog post examines the principles behind how perpendicular recording enables higher storage density than horizontal recording, along with its technological development process.
Hard disks in the information age
The 21st century is called the information age. The greatest challenge for scientists in this era is creating more effective storage devices. Computers store information much like humans do. Humans don’t store information in their mouths; they store it in the brain located in their heads. Just as humans store information in their brains, computers don’t store information just anywhere.
Hard Disk Drive Structure and Operating Principles
Looking at the exterior of a hard disk drive, you see nothing but a protective casing. However, examining the inside reveals the complex design of the hard disk drive. The most important components inside a hard disk consist of the media (the spinning disk), the motor (the motor that spins the media), and the head (a long, slender component resembling chopsticks).
The media is the information storage device. It is a device that performs the recording process, creating a magnetic field to write information, and the playback process, reading the written information, as needed. The magnetic recording process involves sprinkling extremely fine permanent magnetic particles onto the disk. An electromagnet is then moved near the disk, repeatedly reversing its polarity. This process alters the polarity of the attached magnetic particles to the desired orientation. The amount of information a hard disk can store depends on the media’s capacity. Higher media density (more particles per unit area) increases storage capacity.
The Role of the Head and Data Recording Method
The head moves over the media, performing the role of storing and recording information. It can be considered the most critical part of the hard disk. The movement of the hard disk over the media can be likened to the motion of a crane. The head of a hard disk is an electromagnet, a temporary magnet. If you wrap a wire around a nail and connect the wire to a battery, the nail becomes a simple electromagnet. The head also has a wire, called a coil. When current flows through this coil, it becomes an electromagnet like the nail. Writing and reading data on a hard disk is similar to Morse code. Morse code is a signaling system that uses ‘short’ (0) and ‘long’ (1) bursts to exchange signals with another party. Similarly, a hard disk reads and writes data by utilizing the polarity (N, S) of magnets. The magnetic material coated on the media surface represents information as 0 in one direction and 1 in the other direction, depending on the electromagnet’s pole.
For example, suppose you want to store the information “Korea” on a computer. The computer analyzes the text “Korea” and converts it into numbers of 0s and 1s that the computer can understand. Converting “Korea” into 0s and 1s yields the result “01101011 01101111 01110010 01100101 01100001”. When writing this data, the head passes over the media, changing the direction of the current flow as shown in the code above. When reading data from the media, the opposite process occurs. That is, without applying current, an electromagnet passes over the media. It detects whether the electromagnet is (+) or (–) based on the polarity of the magnetic material, inducing a current. This is how the data recorded on the media is read. To explain the head more simply, it’s like a visually impaired person reading a braille book. The head also moves over the media to read the information.
Horizontal Recording vs. Vertical Recording
The traditional data recording method used was horizontal recording. In horizontal recording, the magnetic particles are aligned parallel to the media. In this method, the head creates a magnetic field horizontally. However, as customers and industries demanded higher hard drive capacities, new methods were developed. One of these is vertical recording. The history of perpendicular recording, like that of horizontal recording, began decades ago. Numerous attempts were made to develop perpendicular recording, and the industry finally succeeded in adopting this high-density method. Developing high-density systems requires optimizing both the head and the media, demanding the efforts of countless scientists and engineers. Unlike horizontal recording, this method positions the magnetic particles vertically on the media. Comparing horizontal and vertical recording methods, it’s easy to see that magnetic density has increased. To position the magnets vertically, the head’s storage method also had to change, so information is now recorded vertically rather than horizontally.
The Role and Development of the Motor
The motor in a hard disk performs several roles, but its most important function is to rapidly spin the media. Hard disk motors currently sold on the market typically operate at 5400 RPM. Simply put, this means the motor spins the media 5400 times per minute. Faster motor rotation allows for quicker reading of stored information, thereby increasing computer speed. However, increasing motor speed has the drawback of higher power consumption. Another disadvantage is the increased production cost.
The Future and Challenges of Hard Disk Technology
To develop new hard disks, the storage devices for computers, experts from various fields—electrical engineering, mechanical engineering, materials science, and chemical engineering—must collaborate. Hard disk experts liken hard disk technology to an airplane flying at low altitude. This is because the movement of the head over the hard disk resembles an airplane flying at high speed while maintaining a low altitude. Developing such complex technology requires significant effort and expense.
In recent years, increasing pressure to enhance hard disk performance has led to new technical challenges across various areas, including not only storage capacity but also data transfer speed, reliability, and energy efficiency. For instance, high-speed interfaces like NVMe are being introduced to boost hard disk transfer speeds, while RAID technology is widely adopted to enhance reliability. While these innovations overcome hard disk limitations and open new possibilities, they also bring new challenges such as rising costs and more complex system requirements.
Therefore, future success in this field will depend on developing superior, novel technologies to gain a competitive edge. Research is needed not only to improve existing technologies but also to explore entirely new approaches, and it is anticipated that hard disk technology will evolve through this. The challenges facing scientists and engineers remain significant, but overcoming these challenges will lead to the creation of better storage devices that meet the demands of the information age.
