PMR, SMR, CMR, I-just-want-a-hdd-MR

I recently wanted to buy a new Harddisk. I did not want one that uses "shingled magnetic recording" because thats awfully slow. Instead I looked for a "perpendicular magnetic recording" HDD, but I learned thats not a thing anymore. Instead I could buy CMR disks. For those getting here by google looking for a quick answer: CMR=PMR. For those who want to know why PMR was renamed to CMR and why SMR disks are slow: # How do Harddisks work? Harddisks store information by polarizing small magnets. As you might know, all magnets have a North and a South pole. The writehead of a hdd flips tiny magnets to reflect binary code and a north-south-magnet could mean 1 and a south-north magnet means 0. # LMR Early HDDs used longitudinal magnetic recording. The magnets were flat on the discs. ![LMR]( # PMR Newer harddisks use perpendicular magnetic recording. The magnets were errected so the writehead only "sees" one end of it. This improves storage density a lot. ![PMR]( Today there are 2 diffrent Types of PMR Disks: ## CMR Because the writehead is wider than the magnet track, **conventional** PMR disks had a guard space between the tracks to prevent it from overwriting adjacent tracks. They were the First PMR disks so they were first named PMR. When SMR disks invented, they had to be renamed to conventional magnetic recording because PMR became ambiguous. ![CMR]([Image Source][1] ## SMR In contrast to CMR disks SMR disks do not have guard space. Instead they overwrite adjacent tracks and then rewrite them. Thats why they are so slow: Whenever you write data they actually write a multiple of that. ![SMR]([Image Source][1] [1]:

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4 Replies to “PMR, SMR, CMR, I-just-want-a-hdd-MR”

  1. Perfect and concise explanation.. much appreciated. So it seems that the 16GB Toshiba N300 with helium and PMR may be a good drive for the price. I have always bought CMR (LMR) drives in the past, but I have just bought two 16TB N300 drives to trial. No...I don't work for Toshiba. Thank you again for the concise information.
  2. What about Seagate's common TGMR recording technology? Does it fit into a CMR or SMR category, or one of its own?

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