Disk areal density: Not a constant, consistent platter

I guess you learn something new every day


Comment A disk's areal density varies according to where you look on a platter. This writer had thought it was constant cross a platter but, wouldn't you know it, it's not.

The data recording technology can provide a uniformly dense layer of potential bits across a disk platter's surface but differing track lengths and radii, and head:track angles, make the realisable effective density a variable number.

This issue came to light when trying to understand what were the areal density level rises from current values needed to reach a 1.6Tbit/in2 value with TDMR technology, as Seagate said it would, by being 15 per cent more than current PMR technology could provide.

With current PMR disks being in the 550-750Gbit/in2 area I couldn't see how thus would work. Thomas Coughlin of Coughlin Associates said Seagate had a disk with 826Gbit/in2 areal density.

I queried Seagate on this, who provided details about its 5TB NAS and Enterprise Capacity drive technology: "Both of these drives use the 'Makara' drive for the capacities you refer to. The 6TB Makara is 1TB per platter, six platter configuration. The 5TB from about March onwards will be all six platter configurations also (the 5TB/5 platter being phased out/EOL until about March) ... The areal density for the 6TB and 5TB drives is 633 (GB/in2 avg)."

Note that "avg". Why is that there?

Old_disk_tech_with_head_crash

The good old days: old removable disk (left) and head crash after-effect (right)

Coughlin said: "This is average AD, which can vary by zone. Generally what I track is the maximum AD, that is what is being achieved in the drive or the maximum that current technology makes possible.

"Because of [the] constant speed of the drive and the differences of track length at the various recording radii, as well as complications from the head skew angles, the AD at various parts of the drive can (and will) be different."

"So [the] maximum AD is 826 Gbit/in2 and average is 633 Gbit/in2. It also means you have to ask what AD are, and what we're talking about when we discuss industry trends."

The counter side to this is that when Seagate said its TDMR tech can reach 1.6Tbit/in2 it will be talking maximum areal density and not average.

We can't simply extrapolate disk capacity at today's (average) AD to tomorrow's by applying a simple multiplying factor to the forecast maximal areal density. ®


Other stories you might like

  • Prisons transcribe private phone calls with inmates using speech-to-text AI

    Plus: A drug designed by machine learning algorithms to treat liver disease reaches human clinical trials and more

    In brief Prisons around the US are installing AI speech-to-text models to automatically transcribe conversations with inmates during their phone calls.

    A series of contracts and emails from eight different states revealed how Verus, an AI application developed by LEO Technologies and based on a speech-to-text system offered by Amazon, was used to eavesdrop on prisoners’ phone calls.

    In a sales pitch, LEO’s CEO James Sexton told officials working for a jail in Cook County, Illinois, that one of its customers in Calhoun County, Alabama, uses the software to protect prisons from getting sued, according to an investigation by the Thomson Reuters Foundation.

    Continue reading
  • Battlefield 2042: Please don't be the death knell of the franchise, please don't be the death knell of the franchise

    Another terrible launch, but DICE is already working on improvements

    The RPG Greetings, traveller, and welcome back to The Register Plays Games, our monthly gaming column. Since the last edition on New World, we hit level cap and the "endgame". Around this time, item duping exploits became rife and every attempt Amazon Games made to fix it just broke something else. The post-level 60 "watermark" system for gear drops is also infuriating and tedious, but not something we were able to address in the column. So bear these things in mind if you were ever tempted. On that note, it's time to look at another newly released shit show – Battlefield 2042.

    I wanted to love Battlefield 2042, I really did. After the bum note of the first-person shooter (FPS) franchise's return to Second World War theatres with Battlefield V (2018), I stupidly assumed the next entry from EA-owned Swedish developer DICE would be a return to form. I was wrong.

    The multiplayer military FPS market is dominated by two forces: Activision's Call of Duty (COD) series and EA's Battlefield. Fans of each franchise are loyal to the point of zealotry with little crossover between player bases. Here's where I stand: COD jumped the shark with Modern Warfare 2 in 2009. It's flip-flopped from WW2 to present-day combat and back again, tried sci-fi, and even the Battle Royale trend with the free-to-play Call of Duty: Warzone (2020), which has been thoroughly ruined by hackers and developer inaction.

    Continue reading
  • American diplomats' iPhones reportedly compromised by NSO Group intrusion software

    Reuters claims nine State Department employees outside the US had their devices hacked

    The Apple iPhones of at least nine US State Department officials were compromised by an unidentified entity using NSO Group's Pegasus spyware, according to a report published Friday by Reuters.

    NSO Group in an email to The Register said it has blocked an unnamed customers' access to its system upon receiving an inquiry about the incident but has yet to confirm whether its software was involved.

    "Once the inquiry was received, and before any investigation under our compliance policy, we have decided to immediately terminate relevant customers’ access to the system, due to the severity of the allegations," an NSO spokesperson told The Register in an email. "To this point, we haven’t received any information nor the phone numbers, nor any indication that NSO’s tools were used in this case."

    Continue reading

Biting the hand that feeds IT © 1998–2021