“HAMR” is an abbreviation for Heat-Assisted Magnetic Recording (HAMR) and stands as one of the most significant technological breakthroughs in hard disk drive (HDD) history since PMR/CMR was created. Much like PMR, HAMR is poised to dramatically increase data storage density and, in time, increase performance. Which sounds all well and good… but begs the question: “What exactly is HAMR, and why does it matter so much compared to the previous recording technologies? Now that…. that actually is not an easy question to answer. Certainly not at the fortune cookie/surface level answer levels.
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To start, you need a little context about where the storage industry started… or at least where the “spinning rust” / spindle and platter storage came from. Traditional hard drives have relied on magnetic recording for decades. For a long time, this meant longitudinal magnetic recording (sometimes abbreviated as LMR), where bits were laid out horizontally on the platter—kind of like writing in capital letters on a line in a notebook.
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This worked for a while, but as storage needs ballooned, the industry hit physical limits of this old-school method. As a solution, the switch to perpendicular magnetic recording (aka “PMR” though sometimes called “CMR” or Conventional Magnetic Recording… which yes is technically incorrect terminology as LMR “should be” now known as CMR but only n00bs and “I’m A+ certified” types typically are this autistic) in the mid-2000s allowed bits to be stacked vertically, squeezing data even more tightly on the platter and roughly doubling storage density. That was indeed a huge leap and helped Seagate et al. nearly catch up with Enterprise storage demands.
(Image courtesy of https://blog.westerndigital.com)
Sadly, even PMR has its limits. As the bits got smaller and squeezed closer and closer together, the magnetic materials used became harder to change from storing a 0 to a 1 (and vice versa). Basically, the tiny magnetic “grains” on the disk that hold your data needed to become more and more resistant to accidental phase changes (in layman’s terms, ‘splash damage’ from just being near the bit being actively written to). Thus, stronger magnetic fields to flip their polarity when writing were needed. Creating a “Doom Loop of Despair”… because as this minimum strength requirement got higher and higher, the write heads just couldn’t generate fields strong enough at such small scales without creating more splash damage. Which in turn has led to a pesky problem some have coined as the “magnetic recording trilemma.”
This trilemma is simple to state and yet hard to solve. As mentioned previously, you need bits small enough to hit the ever-increasing density of data you want. You also want those bits of metal’s polarity stable enough to last for the lifespan of the drive (and then some)… but you also need to be able to write them down with the magnet’s field strength you can generate inside such a teeny tiny package. Thus, this trilemma / Doom Loop showed that pushing beyond today’s densities with old-school methods was reaching the limits of practicality when dealing with pesky things like ‘budget’ and ‘mass production scales’. Everyone knew this day was coming, and Seagate (amongst others) took up the quest for the (modern) Holy Grail: a bigger hammer. A big enough hammer to smash the trilemma. A strong enough HAMR to beat those tiny bits (and Mr. Murphy) back into submission. An elegant enough HAMR to not cause ‘splash damage’ when said bits are hammered into submission… and a HAMR technology sophisticated enough to kick this thorny can of worms down the road long enough that a future generation of engineers has to deal with it. Not us. Not now.
(Image courtesy of https://blog.westerndigital.com)
Thus, the mad-genius idea of Heat-Assisted Magnetic Recording. Like all ‘I have an idea’ plans, HAMR is indeed simple in concept but is mind-boggling complex in its execution… and goes something like this: Instead of trying to write data at “room temperature” on stubborn magnetic grains, why not heat the spot you want to write just before trying to flip the polarity? This should allow for even smaller grains of rust that are even more resistant to change at ‘room temperature’ than what isusede now. Sounds like win-win, right?!
After all, “everyone knows” heating a tiny area on the disk makes that spot’s magnetic material temporarily less resistant to changing polarity. Basically, with HAM,R it’s like softening wax before machining—while it’s hot, it’s easy to shape. Once it cools, the magnetic orientation sets firmly in place, locking in your bits securely. If that sounds… “challenging to implement in the real world,” you would be correct. If you think that what is even more challenging is using teeny tiny lasers that fit inside a 3.5-inch form-factor drive, you would also be correct. In fact, it happens via a laser small enough, yet powerful enough, to be embedded rightintoo the write head!
(Image courtesy of https://seagate.com)
That is the 50-foot view of HAMR. Zooming in to be more specific, as per Seagate’s Patent US-11798580-B1, this laser emits light in the near-infrared range, around 830 nanometers in wavelength, that is then focused through an integrated waveguide onto a near-field transducer (NFT), which in turn converts the “light” into localized surface plasmons creating a highly concentrated heat spot at the disk’s recording surface. Or in layman’s terms, a tiny (just beyond visible range) red laser beam “shines” an intense and focused heat beam just nanometers wide on the exact spot on the platter where data is being written. Raising surface temperatures to above 800 °C for a fraction of a millisecond… aka close to or just above the Curie temperature of said media material. In this sweet spot the coercivity of the magnetic medium is dramatically lowered so that the write head’s previously too weak magnetic field can flip the bit easily without accidentally flipping other bits outside this narrow (30nm) zone. Then as the platter rotates away, the heat dissipates rapidly, cooling the spot and “freezing” the data in that tiny grain. All without accidentally changing the parity of surrounding bits on the platter.
This clever combination of light, heat, and magnetics is what HAMR is and using it is what is enabling manufacturers to pack data in at densities previously thought unreachable. Bluntly stated previous technologies (both PMR and Shingled Magnetic Recording) were quickly reaching the point of diminishing returns. Even with the use of TDMR (Two-Dimensional Magnetic Recording) technology PMR’s signal to noise ratio was getting out of hand. So out of hand that musings on upping to the number of read heads packed into each arm was starting to gain traction… which would have been a nightmare from a cost and complexity points of view. SMR and its ‘shingles on a roof’ layout also has major trade-offs—mainly, slower random writes and complicated garbage collection, which absolutely frustrate users with mixed workloads. HAMR, on the other hand, raises the ceiling for storage without those compromises… all by “simply” changing what happens at the magnetic media level itself rather than how tracks are organized or accessed. That is the brilliance of HAMR.
(Image curtesy of https://seagate.com)
But HAMR’s brilliance didn’t just come out of nowhere. Successfully building a HAMR drive meant solving a host of nightmare engineering challenges. How do you focus a laser to a spot so minuscule and keep it stable in a device spinning 7200 times per minute?! How do you find a magnetic alloy that can heat and cool that quickly, thousands of times per second, without degradation? How do you integrate a laser diode inside the tiny write head with reliable power, optics, and cooling, and do all that on a microscopic scale? These were problems scientists and engineers wrestled with for over two decades, requiring advances not just in magnetic materials, but also in photonics, nanotechnology, and thermal management. Seagate, amongst other pioneers, worked on the problem and solved it. One by one… by one. Until finally HAMR was ready for prime time.
Now, from the user’s perspective, HAMR drives don’t feel any different than traditional hard drives. They fit the same 3.5-inch bays, use common interfaces like SATA or SAS, and for most everyday tasks, seem like… well, just really large hard drives. Which is precisely why HAMR, assuming it can gain a reputation for reliability in the coming years, will indeed prove that the billions in R&D Seagate has poured into this technology was money well spent… and not a boondoggle worthy of being called “epic”.
(Image courtesy of https://seagate.com)
Looking forward, HAMR isn’t the end of the story. Research continues into combining HAMR with other evolving technologies, such as Bit-Patterned Media, which can define discrete bits as nano-sized islands for even denser packing; Variations like Multi-Layer or Multi-Level HAMR explore packing more bits vertically within a platter surface. There’s also Microwave-Assisted Magnetic Recording (MAMR), a competing technology using microwave fields instead of a laser to assist in softening the magnetic media. But for now, and the foreseeable future, HAMR is the leading innovation powering the biggest leaps in hard drive capacity.
In summary, HAMR is much more than a technological novelty and rather has the potential be considered the definitive evolution in magnetic recording. One that transforms the very methodology used for magnetic recording and overcomes the physical limitations that constrained decades of prior technology. Ensuring the humble hard drive will continue to evolve quietly behind the scenes. Hopefully evolve fast enough to keep pace with our growing digital world.
