What Is the Difference Between CMR and SMR in HDDs? CMR Is Mainstream for Consumers

The recording method of an HDD refers to the technology that determines how data is recorded on the HDD. The main types are “CMR” and “SMR”.

In recent years, new technologies such as “HAMR” and “MAMR” have also appeared, aiming for even greater storage capacity.

Each of these methods has different features and is optimized for specific uses, greatly affecting the application and performance of HDDs.

Currently, CMR is the mainstream for consumer HDDs, but next-generation technologies like HAMR and MAMR, which enable even larger capacities, are starting to be adopted for enterprise and data center use.

This article also explains the basics of storage standards, mainstream storage configurations, and how to choose based on performance and compatibility.

≫ Related article: How to Choose Storage (SSD/HDD) for Custom PCs [Performance / Features / Compatibility]

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About HDD Recording Methods

Let’s look at the basics of HDD recording methods.

What is an HDD Recording Method?

The HDD recording method is the technology that defines how data is recorded on the magnetic recording layer when saving data.

Depending on the recording method, the capacity, read/write speed, reliability, and manufacturing cost (price) of the HDD are affected.

The recording methods used in recent HDDs are mainly the following two:

• CMR
  A general method that records data so that tracks do not overlap
  
• SMR
  A method that partially overlaps adjacent tracks (shingled writing) to store more data in the same physical size
  

Furthermore, by incorporating the PMR method, which records data vertically on the magnetic disk, into CMR and SMR, even higher-density data storage is possible.

In this way, combining with other technologies can further improve the capacity and performance of HDDs.

In recent years, new technologies such as “HAMR,” “MAMR,” and “TDMR” have also been developed and are starting to be introduced for enterprise use.

Each uses various methods such as lasers, microwaves, and multiple magnetic heads to aim for higher-density data storage (increased capacity).

The details of HDD recording methods will be explained later.

Differences Between CMR and SMR

CMR records data so that tracks do not overlap, while SMR partially overlaps adjacent tracks.

The word “track” has come up, so let’s briefly touch on the structure of an HDD here.

The structure of an HDD consists of a disk for magnetically recording data and a head for reading and writing data.

In the image above, the silver disk is the disk, and the thin triangular shape overlapping the disk is the head.

The disk is usually made of a platter, which is a disk coated with magnetic material on a metal or glass substrate, and it spins at high speed.

It is common for a single HDD to have multiple platters.

In the example image, there are four platters installed.

On the surface of the platter, tracks and sectors for recording data are finely arranged.

Tracks are doughnut-shaped recording areas arranged concentrically from the center to the outer edge of the platter.

Sectors are fan-shaped areas created by dividing the tracks.

Returning to the difference between CMR and SMR, SMR partially overlaps adjacent tracks, while CMR does not.

By partially overlapping, the data capacity per area can increase by about 25% to 30%.

Mainstream HDD Recording Methods

Currently, the recording methods used in HDDs for custom PCs and consumer use are CMR and SMR.

In terms of product numbers, about 90% are CMR and about 10% are SMR, so CMR is overwhelmingly more common.

Therefore, when choosing an HDD, it will almost always be CMR.

SMR may seem better because it increases data capacity, but due to slow write speeds and low demand, it is not used much today.

With SMR, increasing capacity is limited by slow data writing and relocation, so for large-capacity HDDs like 10TB or more, CMR is used.

Also, many users choose CMR for its read/write performance and reliability, and especially for enterprise and NAS HDDs, CMR is in high demand for its reliability, so manufacturers are expanding their CMR lineups.

As a result, the share of SMR products is small, and due to low demand and the inability to overcome slow write speeds, SMR is currently limited to capacities of about 1–8TB.

Types of HDD Recording Methods

We have briefly touched on the main “CMR” and “SMR” recording methods, but there are several other types, which will be explained in detail below.

CMR

CMR (Conventional Magnetic Recording) is a traditional HDD recording method introduced in the 1980s, where data is recorded so that tracks do not overlap.

As the foundation of HDD technology, it has provided stable performance and high reliability for many years, and is still used today for general purposes and systems that require reliability and stable performance.

Even though it is old, it has not been replaced by other methods and remains the mainstream method.

CMR records data so that tracks do not overlap, with the following features:

• Stable read/write performance
  Because the spacing between tracks is even, read/write speeds are stable.
• High reliability
  Performance does not easily degrade even with frequent data overwriting or updates, making it suitable for environments where reliability is important, such as servers and NAS.
• Write speed
  Since tracks do not overlap, overwriting and appending data is easy, and write speeds do not slow down.
• Density limitation
  Compared to SMR and others, recording density for the same physical size tends to be lower, but the structure prioritizes stability and speed.

CMR is widely used where reliability is important.

• General PCs / Workstations
  Used for general purposes and business applications requiring high reliability, suitable for tasks like video editing and design work that require stable performance.
• NAS
  Since multiple users often access simultaneously and stable write performance is needed, CMR is suitable.
• Servers and Data Centers
  CMR is often chosen to maintain reliability and stability in environments that require frequent data updates.

SMR

SMR (Shingled Magnetic Recording) is a method that partially overlaps adjacent tracks (shingled writing) to store more data in the same physical size.

It appeared in the 2010s and was developed to increase HDD recording density.

As mentioned earlier, it may seem good because it increases data capacity, but due to slow write speeds and low demand, it is not used much today.

Main features are as follows:

• High recording density
  By overlapping tracks, data density is increased, allowing more data to be recorded on the same disk size.
• Good cost efficiency
  Increased recording density enables large capacity at low cost.
• Tendency for slower write speeds
  Because tracks are overlapped, overwriting some data requires relocation, which can slow down write speeds. Not suitable for environments requiring frequent rewriting.
• Suitable for archive use
  Effective for uses where data is mainly read and not frequently written, especially when large storage capacity is needed.

SMR is mainly used for applications where write frequency is low and large capacity is needed.

• Backup and Archive
  Since the main purpose is data storage and frequent rewriting is not needed, SMR’s high-density recording is optimal.
• Cold Storage
  In environments where access frequency is low and large capacity is needed, SMR’s cost efficiency is beneficial.

PMR

PMR (Perpendicular Magnetic Recording) is a method that enables higher-density data storage by recording data vertically on the magnetic disk.

It appeared in the early 2000s and was developed to increase HDD recording density.

Compared to the conventional longitudinal magnetic recording (LMR), which recorded data by arranging magnetic material horizontally on the disk surface, PMR greatly increased recording density, allowing for much larger HDD capacities.

PMR itself is not a separate recording method from CMR or SMR, but is a basic magnetic recording technology incorporated into both CMR and SMR.

Features of PMR include:

• Increased recording density
  By arranging magnetic material vertically, track width can be reduced, allowing more data to be recorded on the same physical disk size.
• Improved reliability
  Achieving higher density makes it possible to increase capacity while maintaining stable read/write performance.
• Base technology for CMR and SMR
  It is the base technology for today’s mainstream CMR and SMR, and these methods are based on PMR.

HAMR

HAMR (Heat-Assisted Magnetic Recording) is a method that uses a laser to locally heat the disk surface when recording data, temporarily changing the magnetic properties so that data can be recorded in smaller areas.

This technology appeared in the late 2010s and is attracting attention as a next-generation technology that greatly increases HDD recording density.

It enables high-density data recording that was difficult with conventional technology, greatly increasing recording density.

Features of HAMR include:

• High-density data recording
  Heating with a laser makes the magnetic material easier to record, allowing data to be recorded in narrower track widths. This enables much higher recording density than conventional PMR or SMR.
• Enables large capacity
  HAMR is attracting attention for enabling HDDs with tens of terabytes or more, pushing the limits of recording density.
• Technical complexity
  Precise control of disk surface heating is required, so more advanced and complex technology is needed than before. Manufacturing costs also tend to be higher.

HAMR is mainly being adopted for enterprise and data center use, where large capacity and high density are required.

For example, the following uses:

• Data centers and cloud storage
  Large capacity and highly reliable recording technology are needed to store massive amounts of data.
• Archive storage
  Suitable for environments that need to provide large capacity at low cost for big data backup and archive purposes.
• Enterprise servers
  Expected to be introduced in the future for enterprise server environments where performance and durability in high-density storage are important.

Currently, HAMR is not yet mainstream, but it is expected to become the standard technology for large-capacity HDDs in the future, and its adoption is expanding in fields that require large capacity, such as enterprise and data centers.

Seagate Technology began mass production of HDDs using this method by the end of March 2024, releasing a 30TB model as the first product, and plans to release 40TB and 50TB HDDs around 2025–2028.

≫ External link: The Core of Laser-Heated HDDs: Seagate’s Top Engineer Talks About 20 Years of Struggle (XTECH)

MAMR

MAMR (Microwave-Assisted Magnetic Recording) is a next-generation high-density recording technology like HAMR, but unlike HAMR, which requires laser heating, it uses microwaves to affect the magnetic head and reduce magnetic resistance, allowing data to be recorded at higher density.

Like HAMR, it is a relatively new technology that appeared in the 2020s and is attracting attention as a next-generation technology that greatly increases HDD recording density.

Features of MAMR include:

• Loosens magnetization with microwaves
  When recording data, the magnetic area is temporarily loosened with microwaves to make recording easier. This allows for narrower track widths and higher recording density.
• High reliability
  Compared to HAMR, it does not require heating, so the lifespan of the magnetic head and media can be longer. Also, it is less technically demanding and tends to be lower in cost than HAMR.
• Large capacity
  Enables even higher-density recording than PMR or SMR, making it suitable for large-capacity HDDs.

MAMR is being adopted for enterprise and data center use, where large storage capacity is needed.

Specific uses include:

• Data centers and cloud services
  Attracting attention as a technology to achieve large-capacity storage in data centers handling large-scale data.
• Enterprise storage
  Being used in environments that require high reliability as high-density storage for enterprises.
• Archive and backup
  Because it enables large capacity at low cost, it is suitable for backup and archive of data that needs to be stored for a long time rather than data that is accessed frequently.

MAMR is attracting attention as a next-generation large-capacity recording technology like HAMR, but since it is less technically complex than HAMR, it is easier to commercialize.

Therefore, along with HAMR, it is being introduced as a high-density HDD for enterprise use, and its adoption is expected to expand in the large-capacity storage market in the future.

However, whether MAMR will become mainstream in the market depends on competition with other technologies, cost, and solving technical challenges.

For example, HAMR also aims for high-density recording, and which will become mainstream may change depending on future technological development and market trends.

Currently, MAMR is used in some HDDs, but it is not yet widely adopted, though it may become an important technology in the future.

Toshiba released a 22TB HDD using this method as the first generation in 2021. It seems that a 32TB HDD will be released in 2025.

≫ External link: Successful Demonstration of Over 30TB Nearline HDD (TOSHIBA)

TDMR

TDMR (Two-Dimensional Magnetic Recording) is a method that increases recording density while suppressing interference with adjacent tracks, making it possible to record data at higher density by reading data simultaneously with multiple magnetic heads.

With conventional recording methods, interference between tracks was a problem, limiting the increase in recording density, but TDMR tries to solve this by placing tracks more densely and using multiple read heads to read data.

This makes it possible to store more data on the same physical disk size.

This technology is also a relatively new technology that appeared in the 2020s and is attracting attention as a next-generation technology that greatly increases HDD recording density.

However, it is not yet widely adopted, and there are still technical challenges to practical use.

Features of TDMR include:

• Reading with multiple heads
  TDMR has heads arranged to read data not only from one track but from multiple tracks at the same time. This improves data reading accuracy and enables accurate data retrieval even with high-density recording.
• Enables high-density recording
  Track width can be made even narrower, allowing more data to be recorded in a limited disk area. This enables capacity to be increased beyond the limits of physical space.
• Countermeasure for adjacent track interference (ITI)
  As data density increases, interference from adjacent tracks (ITI: Inter-track Interference) becomes a problem, but TDMR suppresses the effect of interference by using multiple heads.

TDMR is mainly being developed for enterprise and data center use, where high-density data storage is needed. Specific uses include:

• Data centers and cloud storage
  TDMR’s high-density recording is used in data centers that store large amounts of data for long periods.
• Large-capacity enterprise HDDs
  Ideal for storage in enterprise applications that want to maximize recording density.
• Large-capacity backup and archive
  TDMR technology is also needed for storing large amounts of data at low cost.

TDMR is positioned as a next-generation auxiliary technology that enables even larger capacities by combining with existing recording methods such as PMR, CMR, and SMR.

However, since it competes with other new technologies such as HAMR and MAMR, it is not a mainstream technology, but is being adopted for specific uses as a technology to achieve high-density recording.

Summary: Basically, Choosing CMR is OK!

This article introduced the basics of HDD recording methods, the differences between mainstream CMR/SMR, and other recent technologies.

Here are the key points again.

When choosing an HDD for a custom PC, it will usually be CMR in terms of product numbers and capacity.

In addition, to further increase HDD capacity in the future, technologies such as HAMR, MAMR, and TDMR are being developed and introduced.

HDDs using these technologies are for enterprise use and are not yet available in the general market, so honestly, this knowledge is not necessary for building a custom PC.

However, it is interesting to see that the increase in HDD capacity every year is supported by such technological developments.

This article also explains the basics of storage standards, mainstream storage configurations, and how to choose based on performance and compatibility.

≫ Related article: How to Choose Storage (SSD/HDD) for Custom PCs [Performance / Features / Compatibility]

あわせて読みたい

PC Parts Estimation & Compatibility Check Tool

Automatically checks each component you need when selecting parts for a custom-built PC—perfect for beginners.